ultra-fast and green synthesis for water soluble
TRANSCRIPT
Ultra-Fast and Green Synthesis for Water Soluble Polyaniline
and its Applications
PhD Thesis
By
SAMI UR RAHMAN
NATIONAL CENTRE OF EXCELLENCE IN
PHYSICAL CHEMISTRY, UNIVERSITY OF
PESHAWAR, KPK, PAKISTAN
2020
Ultra-Fast and Green Synthesis for Water Soluble Polyaniline
and its Applications
PhD Thesis
By
SAMI UR RAHMAN
A dissertation submitted to the University of Peshawar in partial fulfillment of the re-
quirement for the degree of
DOCTOR OF PHILOSOPHY
IN
PHYSICAL CHEMISTRY
NATIONAL CENTRE OF EXCELLENCE IN
PHYSICAL CHEMISTRY, UNIVERSITY OF
PESHAWAR, KPK, PAKISTAN
2020
i
Abstract
Sami Ur Rahman
Ultra-Fast and Green Synthesis for Water Soluble Polyaniline and its Applications
To search for new materials which are more effective and superior for greater
performance, material scientists worked to developed new routes which are easier, low
cost and environment friendly. Moreover, the time factor is also very important, that how
fast the materials could be prepared. Chemical oxidative polymerization of aniline is a
promising way to tailor the properties and solubility of Polyaniline (PANI). The large
consumption of chemicals and time are still the major drawbacks of this technique. This
research project is designed to synthesize soluble PANI through an ultra-fast and a green
route by using a novel anionic and environment friendly dopant. By this method the ma-
terial was synthesized in a very short period of time (5-10 min.) with excellent yield
(98.62%) and high conductivity (10 S/cm). The synthesized PANI was not only soluble
in water but also in N-Methyl Pyrrolidone (NMP), Dimethyl Formamide (DMF), Dime-
thyl Sulfoxide (DMSO), Tetrahydrofuran (THF) and Ethanol.
After optimization of the reaction parameters, the obtained polymer was system-
atically characterized for physico-chemical and electrochemical properties. Physiochemi-
cal properties such as structural determination, optical properties, morphology, elemental
composition, crystalinity and thermal stability were studied by Fourier Transform Infra-
red Spectroscopy (FTIR), UltraViolet-Visible Spectroscopy (UV-vis), Scanning Electron
Microscopy (SEM), Energy Dispersive X-ray Diffraction (EDX), X-ray Powder Diffrac-
tion (XRD) and Thermogravimetric Analysis (TGA) respectively. These techniques con-
firmed that the dopant phytic acid sodium salt has successfully incorporated into the pol-
ii
ymer chain. Among all the synthesized PANI samples i.e. P-0.5, P-1PA, P-3PA, P-5PA,
P-7PA and P-10PA, the optimized case P-5PA has a desirable nanoscale fibrous porous
interconnected morphology. DC conductivity was measured by Four-Probe Conductome-
ter.
Electrochemical performance was studied by Cyclic Voltammetry (CV), Gal-
vanostatic Charge Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS),
CV and impedance results confirmed that the optimized case i-e P-5PA electrode exhibits
high electrocatalytic performance and capacitive behavior with very low charge transfer
resistance (Rct) of 7.439 Ohm at 0.6 V. To further check the capacitve nature of the elec-
trode material, GCD analysis was performed in both three electrode system and two elec-
trode system. In three electrode system the specific capacitance of the material was calcu-
lated from GCD at various current densities ranging from 1 Ag-1 to 40 Ag-1. At 1 Ag-1, the
specific capacitance was 832.5 ± 1.400 Fg-1 and 528 ± 1.357 Fg-1 at a very high current
density 40 Ag-1. Stability was further checked for 1000 cycles at a high current density of
40 Ag-1 having retention 95.26%.
For practical application, the synthesized material was fabricated into symmetric
supercapacitor device (two electrode system) and was checked by GCD for various cur-
rent densities ranging from 1 to 40 Ag-1. At 1 Ag-1, the capacitance was 531.5 ± 2.177
Fg-1 and 355.35 ± 2.195 Fg-1 at 40 Ag-1. Stability of the device was also checked for
1000 cycles at a current density of 40 Ag-1 having excellent retention i.e. 90%. Further-
more the PANI symmetric supercapacitor showed significant enhancement in both the
energy density and the power density. It delivered an energy density of 73.82 Wh kg-1 at
iii
the power density of 500 W kg-1. More importantly, the energy density was very stable
with the increase in the power density. The energy density reached up to 49.35 Wh kg-1
even at a power density as high as 20000 W kg-1, which was much higher than most of
current commercial supercapacitors.
Furthermore aniline was also polymerized on chitosan film prefabricated on glass
slides to obtain conductive patches. After optimization morphology, elemental composi-
tion and functional groups detection of the Patches were done by SEM, Atomic Force
Microscopy (AFM), EDX and FTIR. Among all the polymeric patches (Patch-0.5, Patch-
1, Patch-3, Patch-5, Patch-7, Patch-10), Patch-5 has a more uniform nanoscale granular
homogeneous surface topography indicating that polymerization of PANI proceeded ef-
fectively and uniformly on the chitosan surface. Sheet resistance was measured by four
probe conductometer. Electronic properies of the optimized conductive polymeric Patch-
5 were studied by CV and UV-vis in phosphate buffer solution (pH 7.4) as a physiologi-
cal medium. The results indicate that our methodology of polymerizing the aniline in the
presence of phytic acid sodium salt as a dopant on the surface of chitosan film leads to a
conductive polymeric patch of chitosan grapted PANI that shows conductivity for ex-
tended period of time (21 days) in physiological conditions. This fabrication technique
for conductive polymeric patches can find applications in the field of tissue engineering,
especially, in cardiac muscles.
iv
Keywords: PANI, Specific capacitance, Chitosan grafted PANI patch, Atomic Force
Microscopy (AFM), Cyclic Voltammetry (CV), Galvanostatic Charge Discharge (GCD),
Electrochemical Impedance Spectroscopy (EIS)
v
Acknowledgements
In the name of Allah, the Most Gracious and the Most Merciful Alhamdulillah, all
praises to Allah for the strengths and His blessing in completing this thesis. Firstly, I
would like to acknowledge my indebtedness and render warmest thanks to my supervisor,
Associate Professor Dr. Salma Bilal, National Centre of Excellence in Physical Chemis-
try (NCEPC), University of Peshawar for her, support, encouragement, exemplary and
exclusive supervision throughout my entire Ph.D study. Her meticulous attentions to de-
tails and insightful comments have helped me shape the direction of this thesis to the
form presented here. Her dedication and enthusiasm for scientific research, her
knowledge which is both broad-based and focused, have always been a source of inspira-
tion.
I would also wish to express my gratitude to Associate Professor Dr Anwar Ul
Haq Ali Shah ICS University of Peshawar for extended discussions and valuable sugges-
tions which have contributed greatly to the improvement of the thesis.
I would like to express my appreciation to the Profesor Dr Abdul Naeen (Direc-
tor) National Centre of Excellence in Physical Chemistry (NCEPC), University of Pesh-
awar for their support and help towards my postgraduate affairs.
My acknowledgement also goes to all the Teaching Faculty, office staffs and
technicians of National Centre of Excellence in Physical Chemistry (NCEPC), University
of Peshawar for their co-operations.
Special thanks are due to my wife, Shehna Farooq, for her continuous support and
understanding, but also for more concrete thinks like commenting on earlier versions of
the thesis, helping with the figures and the final preparation of the manuscript.
vi
It is dept of honor for me to record my appreciation and sincere gratitude to all of
my friends Dr. Noor Saeed khattak, Dr. Muhammad Sohail, Dr. Muhammad Anas, Sajad
Ali Shah, Jangeer Khan and Zia ullah for their kind behavior and sincere wishes.
I am also very grateful to my entire conducting polymers lab fellows, Hajera Gul,
Saba Yameen, bushra Begum and especially Muhammad Arif (just like my brother) for
their assistance and sincere wishes.
I would not have reached at this stage without the prayers, love and moral support
of my parents, brothers and sisters. Last but not least; I would like to thank my mother
who burnt her blood and sweat in nurturing my moral capacities at the first place and
supporting me spiritually throughout my life.
Finally, Alexender von Humboldt Foundation, Germany, Higher Education
Commission Pakistan (project No. 20-1647 & 20-3111/NRPU/R&D/HEC), and NCE in
Physical Chemistry University of Peshawar are highly acknowledged for financial sup-
port.
Sami Ur Rahman
2020
vii
DEDICATION
Dedicated to my Respectable and Loving Parents, wife, Sisters,
Brothers and Teachers who’s Spiritual and Immortal
Love, Blessings, Guidance and Encouragement has always
Helped me at every moment of my life.
viii
TABLE OF CONTENTS Abstract i
Keywords vi
Acknowledgements v
Dedication vii
Table of contents viii
List of Abbreviations and symbols xii
Part A 1
Chapter A1: Ultra-Fast and Green Synthesis for Water Soluble Polyaniline and its
Applications 1
A.1 Introduction 1
A.1.2 Intrinsically Conducting Polymers (ICPs) 2
A.1.3 Charge carriers in ICPs 4
A.1.4 Polyaniline (PANI) 6
A.1.4.1 Structure of PANI 8
A.1.5 Synthesis of PANI 11
A.1.5.1 Chemical Synthesis of PANI 11
A.1.5.2 Electrochemical synthesis 12
A.1.5.2.1 Potentiostatic polymerization 13
A.1.5.2.2 Galvanostatic polymerization 13
A.1.5.2.3 Potentiodynamic deposition 13
A.1.5.2.4 Comparisons between chemical and electrochemical methods 13
A.1.6 Doping in PANI 15
ix
A.1.7 Role of dopants 17
A.1.8 Applications of PANI 19
A.1.8.1 Supercapacitors (SCs) 21
A.1.9 Solubility and Processability of PANI 21
A.1.10 Present Study 23
Chapter: A2 25
A.2 Experimental 25
A.2.1 Materials 25
A.2.2 Synthesis of Phytic acid sodium salt doped PANI in powder form 26
A.2.3 Coating of PANI salt on FTO 28
A.2.4 Fabrication of Supercapacitor device 28
A.2.5 Estimation of percent yield and solubility of the synthesized PANI salts 29
A.2.6 Physico-chemical Characterizations 30
A.2.7 Electrochemical Characterizations 32
Chapter A3 35
A.3 Results and Discussion 35
A.3.1 Polymerization of aniline 35
A.3.2 Influence of Synthesis Parameters on the yield of PANI 36
A.3.2.1 Effect of Monomer Amount on Polymerization Yield 36
A.3.2.2 Effect of Oxidant Amount on Polymerization Yield 37
A.3.2.3 Effect of Phytic acid sodium salt concentration on the yield of polymer 38
A.3.3 Fourier Transformed Infrared (FT-IR) spectroscopy 40
B.3.4 UV-Vis spectroscopy 44
x
A.3.5 X-Ray Diffractrometric analysis (XRD) 46
A.3.6 Elemental composition and Elemental Mapping 48
A.3.7 Scanning Electron Microscopy (SEM) 56
A.3.8 DC Conductivity 61
A.3.9 Thermo Gravimetric Analyses (TGA) 63
A.3.10 Solution Processibility of Phytic acid sodium salt doped PANI 66
A.3.11 Cyclic voltammetry (CV) 68
A.3.12 Galvanostatic Charge/Discharge (GCD) Using Three Electrode System 77
A.3.13 Rate Capability 86
A.3.14 Cycling stability 87
A.3.15 Electrochemical Impedance Spectroscopy (EIS) 88
A.3.15 Fabrication of Symmetric Supercapacitor Device 94
Conclusion 100
Part B 102
Chapter B1: Polymerization of aniline on pre-fabricated chitosan films 102
B.1 Introduction 102
B.1.1 Chitosan 103
B.1.2 Chitosan grafted PANI Composite 105
B.1.3 Application of chitosan grafted PANI 107
B.1.3.1Tissue Engineering 107
B.1.4 Aims and Objectives 109
Chapter B2 110
B.2 Experimental 110
xi
B.2.1 Materials 110
B.2.2 Preparation of chitosan viscous solution 110
B.2.3 Fabrication of chitosan solution on glass slides to obtained chitosan films 110
B.2.4 Synthesis of chitosan grafted PANI conductive polymeric patches 111
B.2.5 Material Characterization 112
B.5.5.1 In vitro characterization physical properties of the patches 112
B.5.5.2 In vitro characterization electronic properties of the patch-5 113
Chapter B3 114
B.3 Results and Discussion 114
B.3.1 Surface Morphology of the Patches using SEM 114
B.3.2 Morphological studies of the Patches using AFM 120
B.3.3 Sheet Resistance of the Patches 128
B.3.4 Energy-Dispersive X-Ray Spectroscopy and Elemental Mapping 129
B.3.5 FTIR Spectroscopy 137
B.3.6 Cyclic voltammetry (CV) 138
B.3.7 UV-Vis spectroscopy 140
Conclusion 143
Future perspectives 144
References 146
xii
List of Abbreviations and symbols
Abbreviations
AFM Atomic Force Microscopy
APS Ammonium Persulphate
CPE Constant Phase Element
CPs Conducting polymers
CT-Complex Charge Transfer Complexes
Csp Specific Capacitance
CV Cyclic Voltammetry
DBSA Dodecyl Benzene Sulfonic Acid
DI H2O Deionized water
EB Emeraldine Base
EIS Electrochemical Impedance Spectroscopy
ES Emeraldine Salt
GCD Galvanostatic Charge Discharge
HOMO Highest Occupied Molecular Orbital
ICPs Intrinsically Conducting Polymers
LB leucoemeraldine
LUMO Lowest Unoccupied Molecular Orbital
NMP N-Methyl Pyrrolidinone
PA Polyacetylene
PANI Polyaniline
PB Pernigraniline
xiii
PPV Poly (p-phenylenevinylene)
PTh Polythiophene
PPy Polypyrrole
RCT Charge Transfer Resistance
RS Series Resistance
SCs Supercapacitors
THF Tetrahydrofuran
1
Part A
Chapter A1
Ultra-Fast and Green Synthesis for Water Soluble Polyaniline and its
Applications
A.1 Introduction
Material science plays a significant role in the development of technology for utiliza-
tion and excellent performance in various practical fields through pure research to fulfill
the human needs. Material development led to tremendously prompt advancement in in-
formation technology, electronics and medical science.
The current exertions in this field look for:
(a) New materials
(b) Development of new and competent methods of material synthesis
(c) Employment of material for advance applications
Historically the science of material and engineering are significant teamsters in
the progress of recent technologies. In contrast with the past, polymeric materials enact
an imperative role in everyday life worldwide because of their wide range of properties.
Latest development in polymer science performs an essential and extending role in a va-
riety of electronic devices, models and applications.
Since recent development in the technologies mainly involves polymeric materi-
als, hence present age can be said to be a polymer age. Revolution in new technological
methods and advancement of current polymer processing technologies are essential for
the expeditious diffusion of these polymeric materials in markets, which authorize them
to expand the application of these novel materials in new fields.
2
Polymers shape our lives because they can be shaped. The utmost driving force at
the back of most research is that to develop plastics fit for electronics and bioelectronics
application. Compared to the metals, polymers have advantage of simple and facile pro-
cessing. Most of the plastics have ability to undergo reversible deformation and ductility,
which is not true for metals. These adorable properties of plastics have attracted many in-
dustrialists and scientist looking for novel applications and new products.
A.1.2 Intrinsically Conducting Polymers (ICPs)
Intrinsically conducting polymers (ICPs) were produced several decades ago [1].
Recently, more than 25 systems of ICPs are known to exist [2]. These are organic poly-
mers having electrical properties just like inorganic metals and semiconductors more
commonly known as “Synthetic Metals”. They have gained immense interest in scientific
and technological applications for their tunable optical and electrochemical properties
with pliability in processing, simple preparation methods and environmental stability.
These includes Polythiophene (PTh) [3], Polypyrrole (PPy) [4], Polyphenylene Vinylene
(PPV) [5] and Polyaniline (PANI) [6] shown in Fig.A.1.1.
The first considerable development in these ICPs was gained in 1977, when Hee-
ger, Mac Diamid and Shirakawa doped (p-type or n-type) polyacetylene chemically and
electro-chemically and thus made it conductible comparable to the metals [7]. They treat-
ed the polyacetylene (PA) films to the vapors of arsenic pentafluoride, chlorine, iodine,
sodium and bromine and observed enhancement in the conductivity of PA films up to
twelve’s orders of magnitude.
After this discovery, some other ICPs have been investigated continuously [8]. In
the year 2000, Shirakawa, Heeger and Mac Diamid were granted with Nobel Prize for
3
their discovery of ICPs. Later on, in the year 2010, Ei-ichi Negishi and Richard Heck
were awarded Nobel Prize for their wok to synthesize pi-conjugated oligomers, den-
drimers and polymers by employing the palladium catalyzed cross coupling reactions.
The discovery of these ICPs with interesting electrical properties was a forward step for
research in the field of CPs.
Most ICPs are malleable and hence can be applied as transparent electrodes in so-
lar cells and electronic devices. These polymers have thermal expansion coefficient and
mechanical properties and make a real possibility for the development of stable conduc-
tive plastic composite components. As they have advantages over metals, metal oxides
and other inorganic compounds, some limitations such as solubility, processability and
stability have prevented the broad utilization of these ICPs in various practical fields.
Therefore, new and improved methods for the manufacturing of these polymers offer
wider marketable interest, suggesting that academically driven development could have
an impact in the market place [9].
n S
n
N
H
n
(a) (b) (c)
n
N
H n
(d) (e)
Figure A.1.1: (a) Polyacetylene (PA) (b) Polypyrrole (PPy) (c) Polythiophene (PTh) (d)
Polyphenylene Vinylene (PPV) (e) Polyaniline (PANI).
4
A.1.3 Charge carriers in ICPs
Generally, polymers are good insulators, but they are doped to achieve higher
conductivities by using different techniques [10, 11]. Therefore, conductivity of ICPs
changes from insulating to metallic state. These polymers have conductivity in the range
from a typical insulator (10-16 to 10-8) (Fig. A.1.2) to typical inorganic semiconductors
(10-4 to 100) to greater than 104 S/cm near to a good conducting metal for instance copper
5×105 S/cm, depending on quality of the dopant along its doping level [12] .
Figure A.1.2: The range of conductivity in CPs from insulator to conductor. (Adopted
from Ref.13).
They have unique chemical structure, but their doping mechanism is completely
different from metals. The doping procedure in these polymers causes redox process
which involves the transfer of charge with the subsequent generation of charge carriers
[14, 15]. The doping agent in this process not only withdraw electrons from the backbone
of the treated polymer but also responsible for the successive addition of electrons to
these polymers. Actually, doping in these polymers involves removing electrons from the
HOMO (highest occupied molecular orbital) of the valence band (oxidation) or moved
electrons to the LUMO (lowermost unoccupied molecular orbital) of the conduction band
5
(reduction). Thus, production of polaron, soliton and bipolaron (Fig. A.1.3) takes place
by redox process which is actually charge carriers. Based on bond structure in the ground
state, these ICPs are classified into degenerative and non-degenerative systems.
Polymers with degenerative system possess two structures with identical geome-
try in their ground state. On the other hand, the polymers with non-degenerative system
possess two different geometric structures with different amount of energy in their
ground state. These different geometric structures of non-degenerative system are ben-
zenoid and quinoid. The benzenoid structure have low energy than quinoid one. The
charge carriers in the degenerate system are called solitons. On the other hand, polarons
and bipolarons act as a charge carrier in both cases either the system is degenerative or
non-degenerative such as PPy, PTh and PANI [16, 17]. Therefore, these polarons and bi-
polarons are responsible to produce conductivity in these polymers.
Generally, P-type doping and N-type doping is involved in the oxidation and re-
duction process [18]. As redox potential site is present at each polymeric repeat unit.
Therefore, charge carriers having high density are beneficial for the doping of conjugated
polymers. Generally, these polymers undergo p-type doping because of high density of
П-electrons system [19].
In p-type doping, there is an electronic movement from the HOMO level of the
polymer to dopant that results hole formation in the polymer backbone. Whereas n-type
doping involves an electronic movement from the dopant to the polymer (LUMO) and
consequently, electron density increases. Therefore, density of the electrons and move-
ment of the charge carriers can be altered by the process of doping in these ICPs [20, 21,
22].
6
Figure A.1.3: Conduction mechanisms in ICP with degenerated ground state (Adopted from
Ref. 23).
A.1.4 Polyaniline (PANI)
PANI is an ICP having repeat units up to 1000 and was first reported as aniline
black in 1862 [24]. This is one of the most useful and unique in the class of ICPs because
of its environmental stability both in doped and de doped forms, and its unique acid-base
chemistry [25]. This unique ICP has several potential applications in sensors, corrosion
protection, separation membrane, surface coating, batteries, drug delivery, supercapaci-
tors (SCs) and tissue engineering [26, 27]. This stable and tunable ICP can be synthesized
in several forms for instance films, powder and fibers with the possibility of low-cost,
easy synthesis, and bulk production.
7
In 1907 and 1909 Wills Tatter and coworker [28] described aniline black as eight
nucleus chains having indamine structure (Fig. A.1.4). In 1911, the electrical conduction
of this polymer is reported in organic acids [29]. Surville et. al. [30], investigated the ex-
change of proton of PANI along with its redox properties. Although in 1977 it gained full
attention, when it was discovered that iodine doped polyacetylene (PA) has metal like
conductivity [31, 32]. In the beginning of 20th century work was started on its production
and its intermediate products [33].
N
N
N
N
H
H
N
H
N
H
N
H
N
H
N
HH
H
Figure A.1.4: Eight nucleus chains compound have indamine structure [28].
The first well detailed report on PANI was given by Woodhead and Green [32].
They report the following constitutional aspects of this polymer.
1. From leucoemeraldine that is the parent compound four quinoid stages are derived.
2. Primary oxidation of aniline is the minimum molecular weight accordance to the eight
nucleus present in its structure.
3. One oxygen atom consumed in the conversion of emeraldine to nigraniline.
4. Two oxygen atoms consumed in the conversion of emeraldine to pernigrailine.
5. One oxygen atom is consumed in the conversion of nigraniline into pernigraniline.
6. Four hydrogen atoms are consumed in the reduction of emeraldine to leucoemeraldine.
7. Six hydrogen atoms are consumed in the reduction of nigraniline to leucoemeraldine.
8
8. While eight hydrogen atoms are consumed in the reduction of pernigraniline to leu-
coemeraldine.
Tremendous research has been done on PANI in the last 30 years. However, in the
last five years, a lot of papers have been published on this conductive polymer; indicate it
is still under examination. PANI is inexpensive to produce and have attractive properties
for applications such as relatively lightweight, corrosion protection and exhibit excellent
matrix adhesion. Beside this, the electrochemical properties of PANI depends on the sub-
stituents presence in it, dopant and some other conditions including temperature, time etc.
during its synthesis. These properties exemplify the tailorability of PANI for applications
in various fields [17]. From ICPs, PANI is the most widely studied and an exclusive pol-
ymer for the following excellent properties:
1. Easy methods of it synthesis.
2. It is the only polymer whose electrical properties can be controlled by protonation.
3. For its excellent and interesting electrochemical behavior.
4. This polymer shows stability in the environment.
5. For its easy non-redox doping by protonic acids.
A.1.4.1 Structure of PANI
For the first time, Green and Woodhead described the structure of PANI [32], as
shown in the Fig. A.1.5.
Figure A.1.5: Chemical structure of PANI.
NH NH N N
y 1-yx
9
They report that in the structure of PANI, Aniline monomers coupled head to tail with the
aromatic ring at para position in the polymer chain. PANI is a phenylene based ICP with
a malleable (-NH) group which flanked by phenyl ring on either side. Thus (-NH) group
produce diversity in various properties of PANI [34].
The oxidation configuration of PANI can be varied from completely reduced to
completely oxidized state [35]. The structures of its principal states are presented in Fig.
A.1.6.
Figure A.1.6: Various redox forms of PANI.
NH NHHN
HN
n
N N N N
n
Emaraldine Salt (Green)
Pernigraniline (Violet)
NH NHHN
HN
n
NH NH N
n
Leucomeraldine (Pale Yellow)
N
Emaraldine Base (Blue)
10
These different states of PANI can easily be transformed to one another by redox process
(Fig. A.1.7).
Figure A.1.7: Scheme for Interchange of various redox states of PANI.
There are three main oxidation states of PANI depending on the reduced and oxi-
dized repeating units in PANI structure. Fully reduced state (1-y = 0) of PANI is termed
as leucoemeraldine (LB), Pernigraniline (PB) is its fully oxidized (1-y = 1) form. Emer-
aldine base (EB) is half-oxidized form of PANI. Technologically, EB is the most signifi-
cant form of PANI relative to its other states, owing to its high environmental stability
and facile doping which results its conversion to emeraldine salt (ES), the only conduct-
ing state of PANI [36].
NH
NH
N N
NHHN NH N
HN
HN
+2H
+e+H+e
+H
+e +H+e
ES EB
PN PN
Emaraldine Salt
Leucomeraldine (Pale yellow)
(green)
Pernigraniline Salt (Blue) Penigraniline (Violet)
Emaraldine Base (Blue)
11
A.1.5 Synthesis of PANI
For the synthesis of PANI, several methods are available in literature on the struc-
tural and constitutional aspects of aniline polymerization. From all these methods, oxida-
tive polymerization of aniline is very popular. In this method
polymerization and doping of the monomers occurs at the same time. This oxidative
polymerization for the synthesis of PANI may be carried out either chemically or electro-
chemically [37].
A.1.5.1 Chemical Synthesis of PANI
The chemical synthesis of PANI has been done in the aqueous medium by treat-
ing the monomer Aniline with the dopant and an oxidizing agent [38]. The main purpose
of the oxidant is to take out a proton from the molecule of aniline and form a weak coor-
dination bond with the intermediate of the polymerization reaction or with the final prod-
uct [10, 39]. A very small quantity of the dopant is also used to prevent the synthesized
polymer of the polymerization reaction from oxidative degeneration. In this chemical
method, by a redox process the chain of the polymer proceeds with the addition of the
monomers to the end of the polymer (Fig. A.1.8).
N
H
H- e
N
H
H N
H
N
H
H N
H
H
H
+
-2H
N
H
N
H
Aniline
AnilinePolyaniline
Figure A.1.8: Polymerization of Aniline.
12
The experimental procedure for polymerization comprises the addition of oxidant
to the mixture of Aniline/dopant. The mixture solution is stirred continuously to about 24
hours till mixture solution color turned to dark green. This dark green precipitate is re-
moved by the process of filtration. This product is washed with acetone in excess, after
washing the product is dried very well under vacuum for 48 hours [37]. This obtained
product is simply called emeraldine salt form of PANI. The emeraldine salt can be trans-
formed to the basic state of PANI when it is treated with aqueous solution of ammonium
hydroxide solution for 15 hours. The obtained product is washed and dried well which is
the emeraldine base form of PANI [40].
Many other methods such as solution polymerization, interfacial polymerization,
suspension polymerization, emulsion polymerization etc. are also used for the chemical
synthesis of PANI [39].
A.1.5.2 Electrochemical synthesis
The electrochemical preparation of PANI is an electro organic process, because in
this method more stress is given on the electrochemistry of the process rather than simple
organic synthesis (chemical method). Electrochemistry has performed a considerable
function in the development of organic ICPs. For most applications these ICPs in the
form of thin films with large surface area is very crucial. The electrochemical method is a
standard one to synthesize thin films of PANI [41, 42]. The study of its electrical and op-
tical properties is carried out in-situ by electrochemical techniques. The electrochemical
production of PANI is just like the electro deposition of metal from the solution of elec-
trolyte bath. Electrochemical synthesis of PANI can be done by using three well known
techniques, namely, potentiostatic, potentiodynamic and galvanostatic methods [43, 44].
13
A.1.5.2.1 Potentiostatic polymerization
In this technique, current is observed while controlling the electrode potential
[43]. This process shields the reliability of the coated material; therefore, it provides an
ideal platform for the construction of biosensors. The variation in the electrical current in
this method of polymerization depends on several aspects including plating conditions
and the coated material, hence, the application of coulometer is obligatory to control the
polymer thickness deposited on the electrode surface [43].
A.1.5.2.2 Galvanostatic polymerization
In this technique, current is controlled while potential of the electrode varies. This
technique is very useful as it provides the best control over the polymerization by main-
taing the polymerization conditions throughout the whole deposition period [43].
A.1.5.2.3 Potentiodynamic deposition
In this technique, the potential of the electrode changes at selected scan rate
through electrolyte [45, 46]. Deposition of the material takes place in layers while retain-
ing the electrocatalytic activity of each layer before the synthesis of next layer [38]. This
technique produces different surface morphology of the polymer to the potentiodynamic
and galvanostatic polymerization [45]. It has been observed that potentiostatic and gal-
vanostatic methods produced a globular and porous morphology while fibrous and rod
like morphology is obtained by using potentiodynamic method [45].
A.1.5.2.4 Comparisons between chemical and electrochemical methods
Chemical synthesis of PANI requires slow mixing of the monomer solution with
oxidizing agent [47, 48]. Although this process results the formation of irregular and ag-
gregated particles of PANI powder in bulk but the PANI solution can be casted on any
14
substrate either conductive or nonconductive. This property gives chemical synthesis ad-
vantage over electrochemical in which substrate must be conductive. Therefore, chemical
synthesis is mostly employed method for commercial applications [48, 49]. Additionally,
variety of ICPs can be synthesized by using chemical method even those which are not
favorable for electrochemical synthesis [50].
Regrettably, chemically synthesized polymer has lower conductivity when the
same polymer produced by electrochemical method [49]. Furthermore, the electrical
properties of the chemically synthesized polymer is greatly affected by the purity and
solvent chosen, the reagents concentration, stirring rate, the dopant, oxidant, and reaction
time, therefore optimization of all these parameters in chemical synthesis making it diffi-
cult to use [49, 51, 52, 53].
Electrochemical synthesis of the polymer occurs by providing current between the
electrodes kept into the mixture having precursor, dopant and solvent [54, 55, 56], that
resulted in the deposition of polymeric film on the electrode surface having controlled
thickness [43]. In this method, monomers oxidize on the working electrode having posi-
tive charge and results the formation of insoluble polymer film [50]. Properties of the
electrochemically prepared film of the polymer will be defined by the deposition time,
doping agent, electrode system, temperature and solvent [57, 58, 59]. Moreover, through
this process only those monomers can be polymerized which have ability to oxidize un-
der the influence of applied potential [50].
Electrochemical polymerization enables the rapid in situ deposition of ICPs, but
when the bioactive molecules are used as dopant, the situation becomes inverse which
causes the limitation of using electrochemical method [60]. Beside this, shapes and yield
15
of the material is highly sensitive to the electrode surface area and geometry that is used
for the deposition of material in electrochemical technique [61]. Therefore, such require-
ments for an electrode make the creation of composite difficult with this process [62]. On
the other hand, composites can be easily produced by chemical method [60].
Generally, it is seen that any efforts to improve a particular property of PANI
leads to decrease in other valuable properties. For example, electrochemically synthe-
sized PANI have enhanced electrical properties but limited solubility in common organic
solvents along with its very low yield limits its use at industrial scale. On the other hand,
chemically synthesized PANI shows comparatively good solubility and good yield but at
the expense of conductivity. The properties of the PANI suggest it to be very suitable for
a wide range of applications. In this view, PANI needs to be synthesized and collected in
such a form where it can retain all its desirable properties like solubility, conductivity,
stability and so on. So, it is worth to develop such polymerization technique which pro-
duces PANI with all the desirable properties.
A.1.6 Doping in PANI
Two significant approaches have been employed to achieve ES form of PANI. a)
doping of half oxidized state (EB) through protonic acid and b) doping of fully reduced
state (LB) through oxidative doping (p-type). Therefore, PANI has the ability to undergo
p and n type doping. This doping process produces positive or negative charge carriers
(i.e. polarons and bipolarons) [63]. These positive or negative charge carriers cause delo-
calization in the polymer backbone and thus make this polymer conductible. Generally, it
is believed that in n-type doping, charge carriers are not stable. So, doping of PANI
through p-type is more popular for practical applications in various fields [64]. Therefore,
16
from the class of ICPs, PANI is a unique, because its conducting behavior is controlled
either by oxidation or protonation. These two methods of oxidation and protonation are
shown in the Fig. A.1.9.
HN
HN
HN
HN
HN
HN
HN
HN
A
x
x
HN
HN N
HN
x
A
A
Leucoemeraldine base
Emeraldine Base
Emeraldine salt
+ 2H+
+ 2A- Acid Doping
- 2 e+ 2 A
Oxidative Doping(Chemical or electrochemical)
Figure A.1.9: Doping mechanism of PANI [63].
It can be observed that same product (ES) is obtained through both types of dop-
ing. However, protonic acid doping induces charges through protonation without affect-
ing the PANI oxidation state by maintaining its structural identity because of the strong
organization of σ bonds that are critically intact. The charge transfer generally occurs to
or from the conjugated system, leads to the significant alteration of electrochemical and
17
physical properties of the polymer. Relative to the other properties, doping performs an
essential role to enhance the polymer conductivity over several orders of magnitude [65].
A.1.7 Role of dopants
Literature survey reveals that extensive studies have been carried out to increase
the physical and electrical properties of PANI. The properties of PANI depend mainly on
the dopant ions used, which further depend on the type of the dopant used. Generally, in-
organic acids e.g. phosphoric acid (H3PO4) [66], sulfuric acid (H2SO4) [67], hydrochloric
acid (HCl) [68], molybdic acid (H2MoO4) [69],tungstic acid (H2WO4) [70], perchloric ac-
id (HClO4) [71], and organic acids e.g. camphorsulphonic acid (C10H16O4), phe-
nylphosphonic acid (C6H7O3P) [72], dodecylbenzene sulfonic acid (DBSA)
(C12H25C6H4SO3Na) [73], benzoic acid (C7H6O2) [74], oxalic acid (C2H2O4) [75], 5-
sulphosalicylic acid (C7H6O6S), and p-toluenesulfonic acid (PTSA) (CH3C6H4SO3H)
[76], are used for the doping of PANI.
Usually, organic acids dopants showed better doping effect than inorganic acids
for processibilty [77]. Although high conductivity is obtained by doping PANI with inor-
ganic acids but there are several limitations such as: 1) undesirable morphological fea-
tures [78], 2) Show poor solubility in water and other common polar organic solvents
[79], 3) Product formed by inorganic dopants are generally difficult to process due to its
less solubility which is the main barrier for its chemical manipulation and potential use
[80], 4) Doping of PANI with small inorganic dopants losses its conductive nature in
neutral or basic medium which limits its application in biomedical fields [81]. While
PANI doped with organic acids show good morphological features and high solubility
and hence processability on expense of its electrical properties.
18
Therefore, it is necessary to synthesize PANI with an appropriate dopant to im-
prove both the processability and electrical properties of PANI. Among various organic
dopants, Phytic acid (Fig. A.1.10) has been investigated an abundant natural plant de-
rived pollution free compound contain six phosphates and having a good solubility in wa-
ter. The Phytic acid can act both as a dopant and cross-linker and form phosphorized
PANI with a net-like structure. This organic dopant act together with a number of chains
at a time, therefore tendency towards non-favorable spiral structure is lower than small
and non-cross-linking anions such as chlorides, sulphates and nitrates [82].
Pan et al. [82] used phytic acid, both as a dopant and gelator to form a conducting
polymer powder or hydrogel network. The synthesized hydrogels showed excellent elec-
trical conductivity in neutral condition. Beside this the synthesized material was used as
electrode material in supercapacitor with specific capacitance (480 Fg−1).
Hui Huang et al. [83], successfully synthesized PAni nanofibers using phytic acid
as a dopant. The synthesized nanofibers with greater surface area, good conductivity with
more active sites were used as ideal materials for detection of heavy metal ions.
Comparative study of undoped PAni, H3PO4 doped PANI and phytic acid doped
PANI was reported by Xiaohui Gao and its coworkers [84], and found high conductivity,
high thermal stability and best anticorrosion properties of phytic acid doped PANI among
the three samples.
Sungjin Im, et al. [85], synthesized HCl and phytic acid doped polyaniline nano-
fibers, via radical polymerization in a hydrochloric acid and a phytic acid solution respec-
tively. They investigated that the Phytic acid doped PANI NFs showed greater capaci-
19
tance 227 Fg-1, than the HCl doped PANI i.e. 105 Fg-1 at 30 Ag-1, due to the enhanced
electrical conductivity caused by Phytic acid doping. On the basis of above literature,
phytic acid and probably its salts (Fig. A.1.10) can effectively dope the polymers with
improved processability and electrical properties.
OPO3H2
OPO3H2
OPO3H2
OPO3H2
OPO3H2H2O3PO
Phytic Acid
OPO3Na2
OPO3Na2
OPO3Na2
OPO3Na2Na2O3PO
Phytic Acid Sodium Salt
Na2O3PO
Figure A.1.10: Chemical structure of phytic acid and its sodium salt.
A.1.8 Applications of PANI
PANI is exceptional and interesting among other ICPs because of its tunable con-
ductivity that can be modified either electrochemically or chemically [86]. This conduct-
20
ing polymer has gained substantial attraction due to its wide applications like supercapac-
itors [87, 88], biosensors [89], batteries [90], electrostatic dissipation, surface coating, ac-
tive deliver, electrochromic devices, filtration membrane, solar cells, electromagnetic
shielding, nonvolatile memory devices and tissue engineering (Fig. A.1.11). PANI have
become attractive for these applications for its facile synthesis, low cost, high electro-
chemical activity, ease of synthesis and high thermal stability as compared to other ICPs
[91].
Figure A.1.11: Applications of PANI in various fields.
Due to its excellent environmental stability and electrocatalytic activity, PANI is
considered promising material for various applications [92, 93, 94].
21
A.1.8.1 Supercapacitors (SCs)
Supercapacitors (SCs) have attracted immense attention in modern electronic
technology. They are efficient energy storage devices with an exclusive capability to
store the charge and then deliver it much faster [95, 96]. They store charge at interface of
electrode/electrolyte. The amount of stored energy in SCs derives from non-faradic cur-
rent and pseudocapcitance. Charging of double layer is responsible for the origination of
energy from non-faradic current, while energy of the pseudocapacitance comes from fa-
radic current which arises by the oxidation/reduction processes occur at the electrode sur-
face deposited with active material [97, 98]. They store capacitance of a higher magni-
tude with excellent reversibility than conventional electrochemical capacitors [99, 100].
Up to date materials that have been used as electrode in SCs include carbon, metal
oxide such as RuO2, NiOx [101, 102] and more recently ICPs [103]. In all these elec-
trodes materials, ICPs are typical examples of pseudocapacitance performance because
they provide a constant range of oxidation states by increasing the potential of the elec-
trode and thus increased capacitance of the capacitors [104]. Of all investigated ICPs,
PANI is perhaps the easiest and cheapest to synthesize chemically or electrochemically in
various aqueous media. Also doped PANI is much more conductive in comparison to the
other common ICPs. It is extremely stable either in dry or wet air and undergoes kinet-
ically fast doping/dedoping mechanism [105, 106]. Therefore, high capacitance of PANI
makes it promising and emerging electrode materials in SCs [107].
A.1.9 Solubility and Processability of PANI
Normally chemically synthesized PANI shows better solubility compared to elec-
trochemically synthesized PANI. Generally, acidic medium is required for the prepara-
22
tion of PANI. In this process, acid performs the function of dopant which significantly
changes the properties of the material, more specifically, electrical conductivity and solu-
bility. Literature survey reveals that inorganic acids such as H2SO4, HCl etc are the best
doping agents for the enhancement of stability and conductivity of PANI [66-71]. But the
major drawback of using inorganic acids is insolubility of the synthesized material in
common polar organic solvents, as poor solubility of the material limits its applications in
various fields [78-81]. Ample attempts have been made to enhance these characteristic
properties of PANI [66-78].
In view of this, various synthetic routes towards soluble PAni include the synthe-
sis of PANI derivatives and its copolymers [79]. These methods are promising ways to
increase the solubility and hence processability of PANI. But solubility is attained at the
expense of conductivity. These two parameters are also beneficial for the capacitive
properties of the polymers. In addition to these, the large consumption of chemicals and
longer time for polymerization are also the major drawbacks of such techniques.
Motivated by these challenges and in search of all in one solution to the problems,
here we report ultra-fast and green synthetic route for synthesizing highly soluble and
highly conductive PANI salts by using phytic acid sodium salt as a novel organic dopant.
Phytic acid sodium salt is an abundant natural plant derived pollution free compound
contains six phosphates and having a good solubility in water. The Phytic acid sodium
salt can act both as a dopant and cross-linker and form phosphorized PANI with a net-
like structure. This organic dopant act together with a number of chains at a time, there-
fore tendency towards non-favorable spiral structure is lower than small and non-cross-
linking anions such as chlorides, sulphates and nitrates. By using this dopant the
23
polymerization time and use of toxic chemicals is greatly reduced in comparison to the
previously reported methods. The novel dopant seems to furnish a complementary set of
electrochemical and morphological properties to PANI chains.
A.1.10 Present Study
Lots of work has been done on PANI but much more is needed to be done in order to
reduce the cost and time of synthesis, generation of byproducts, and need of washing the
final product with hazardous chemicals but without compromising its useful properties.
That can be done by proposing new synthesis routes, or reactants required for oxidation
and polymerization of aniline. In this context the present study is aimed to provide a flex-
ible, cost-effective, ultra-fast and ultra-green process for the synthesis of highly conduc-
tive and highly soluble PANI by using phytic acid sodium salt as a novel dopant, where
the polymerization time and use of toxic chemicals could be reduced in comparison to
the previously reported methods. It is expected the resultant PANI material will show
solubility in various polar organic solvents and also in water on account of the incorpora-
tion of proposed dopant. We hope that the synthesized material will exhibit high electri-
cal behavior due to the interaction of highly phosphorized novel dopant and allow the use
of simple and low-cost solution processing techniques to process this material in the form
of composites and films.
Different physico-chemical techniques will be employed to characterize these materi-
als for exploring their physical and chemical properties. In addition to these, capacitive
properties of the synthesized material in three electrode system will be evaluated by using
various electrochemical techniques such as Cyclic Voltammetry (CV), Galvanostatic
Charge Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The mate-
24
rial will also be fabricated as PANI based symmetric device. The device will be evaluated
for specific capacitance, rate capability, cyclic stability, energy density and power density
by GCD.
25
Chapter A2
A.2 Experimental
A.2.1 Materials
All chemicals used in this research project were analytical quality and were re-
ceived and used without further purification except Aniline. Aniline was freshly double
distilled to remove any type of impurities. After double distillation, the aniline was kept
in the refrigerator for further use. Fluorine doped Tin Oxide (FTO) glass (13 Ω/sq) was
obtained from Solaronix. All these chemicals are listed below in the Table A.2.1 with
molecular weight along with the name of company. All the samples prepared in the Pyrex
glass made glassware. Deionized water was used in all this study for samples synthesis
and washing purposes.
Table A.2.1: Reagents used in the current study.
S. No Reagent Formula Mol. Weight Company
1 Sulphuric acid H2SO4 98.08 Scharlau Spain
2 Hydrochloric acid HCl 36.46 Scharlau Spain
3 Aniline C6H5NH2 93.13 Sigma Aldrich USA
4 Phytic acid sodium salt C6H17NaO24P6 682.01 Sigma Aldrich USA
5 Dimethylformamide C3H7NO 73.09 Sigma Aldrich USA
6 Dimethyl sulfoxide C2H6OS 78.13 Sigma Aldrich USA
7 Ammonium persulphate (NH4)2S2O8 228.18 Sigma Aldrich USA
26
A.2.2 Synthesis of Phytic acid sodium salt doped PANI in powder form
Various concentrations of phytic acid sodium salt were used for the synthesis of
different samples of phytic acid sodium salt doped PANI. All the samples names along
with their codes are shown in the Table A.2.2.
Regarding phytic acid sodium salt solutions (0.5%, 1%, 3%, 5%, 7% and 10%
(w/v) were prepared by dissolving in DI H2O at room temperature. When the phytic acid
sodium salt solutions become ready, then 2.5 ml from each concentration of phytic acid
sodium salt solution i-e 0.5%, 1%, 3%, 5%, 7% and 10% (w/v) and 0.0055 moles of ani-
line were mixed in 5 ml DI water and these combined solutions were termed as solution
‘A1’, solution ‘A2’, solution ‘A3’, solution ‘A4’, solution ‘A5’ and solution ‘A6’.
For the preparation of oxidant solution, 0.001M solution of APS was prepared by
dissolving 0.0078 moles of APS in 15 ml of DI water, and this solution was termed as so-
lution ‘B’ for each sample.
For further utilization, these solutions were kept in refrigerator for 15 minutes.
After refrigeration, for sample 1, 1 ml from solution A1 and 0.5 ml from solution B, , for
sample 2, 1 ml from solution A2 and 0.5 ml from solution B, for sample 3, 1 ml from so-
lution A3 and 0.5 ml from solution B, for sample 4, 1 ml from A5 and 0.5 ml from solu-
tion B, for sample 5, 1 ml from A5 and 0.5 ml from solution B and for sample 6, 1 ml
from A6 and 0.5 ml from solution B in 2 ml Ependoff tube (Fig. A.2.1). When these two
solutions for each sample were mixed, they were shacked quickly with hand. After 10-15
minutes, there appears a color change of the mixture from milky to dark green, shows
that polymerization of aniline has taken placed. The resulted product was put on the filter
paper for washing. The product was extensively washed with acetone, to wash out any
27
excess of the dopant, uncross-linked polymeric chains and any side products. After wash-
ing the product was dried well and stored for further physico-chemical and electrochemi-
cal characterization.
Figure A.2.1: Synthesis of powder PANI. (A is the solution of phytic acid sodium salt
and aniline in DI water and B is the solution of APS in DI water)
Table A.2.2: Design of powder samples composition and their Codes.
Samples Composition Code
0.5% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS P-0.5PA
1% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS P-1PA
3% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS P-3PA
5% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS P-5PA
7% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS P-7PA
10% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS P-10PA
28
A.2.3 Coating of PANI salt on FTO
For the preparation of FTO electrodes based on PANI salt, FTO glass (2×2 cm2)
(Fig. A.2.2 a) was cleaned with DI water and acetone. 2 mg of polymer was drop coated
on conductive surface of FTO (Fig. A.2.2 b). The coated FTO was then dried at 50°C for
10 minutes. Another electrode having same dimension and same mass of active material
was also prepared.
Figure A.2.2: (a) Un-coated FTOs (2×2 cm2)
Figure A.2.2: (b) PANI-coated FTOs (2×2 cm2)
A.2.4 Fabrication of Supercapacitor Device
For device fabrication as displayed in Fig. A.2.3 a, two prefabricated FTO”s
sandwiched a filter paper (Whatmann filter paper with pore size of 20-25 μm) in such a
29
way that one end of the filter paper was protruding out for providing the electrolyte. The
filter paper can also act as a separator. This sandwich type cell was then gripped by using
clips and its illustration is FTO/PANI-Separator-PANI/FTO as shown in Fig. A.2.3 b.
Figure A.2.3: (a) PANI based fabricated device
Figure A.2.3: (b) Schematic illustration of device
A.2.5 Estimation of percent yield and solubility of the synthesized PANI salts
% yield of the prepared PANI samples were estimated by applying the following
expression:
% yield = (Weight of PANI/Weight of Aniline + Weight of dopant) ×100
30
Where, weight of PANI was calculated by subtracting weight of empty petri dish
from total weight of petri dish containing dried PANI which was obtained at the end of
experiment.
In order to check the solubility of the as prepared PANI in various polar solvents,
following procedure [108] was employed. 10 ml of each solvent was taken in tagged bot-
tles followed by slow addition of the sample to these and shook well. If after shaking,
some quantity of the polymer remained in the solutions, then few drops of the solvent
were added to dissolve it completely. After this, solubility of the synthesized material in
each solvent was calculated in w/v %.
A.2.6 Physico-chemical Characterizations
All the samples were characterized by FT-IR Spectrometer (Shimadzu, Tokyo,
Japan) for functional groups conformation. Potassium bromide (KBr) pellets were pre-
pared and used for blank analysis. For sample analysis 5% solution of each sample was
mixed with KBr powders for thin pellets preparation and spectra were recorded from
400-4000 cm-1.
Absorption analyses of all PANI samples dissolved in DMF were carried out by
using a Perkin Elmer spectrophotometer in a spectral range of 300-1000 nm.
To investigate the structure of the materials that it is crystalline or amorphous, X-
ray Diffractomer (Model: JDX 3532 JEOL) Japan was used, with a radiation wavelength
(λ) of 1.54 Å. An appropriate amount of each sample was placed in a tube generating X-
ray for analysis applying 35kV voltage and 20 mA currents. During analysis scanning
degree was in the range of 10-50o.
31
For the elemental composition and mapping, all the samples were characterized
with the help of Helios G4 CX FEI Deutschland GmbH.
For surface morphology, all PANI samples were analyzed by SEM (Helios G4
CX Dual Beam microscope equipped with Octane Elite) within the voltage range of 5
kV. To transform the sample for SEM a suitable amount of each sample was placed on
Aluminum stubs by using conductive taps. For each sample image was taken using a fo-
cused electron beam under suitable resolution and voltage.
The conductivity of all the prepared samples was checked in the form of well
dried pellets by using Four Probe Conductometer (Jandel RM 3000) equipped with a po-
tentiostate at room temperature. The pellets (diameter: 13 mm and thickness: 5 mm) were
made by hydraulic press using a pressure of 15 tons. Resistivity was calculated using the
equation 1[109]:
ρ = 2 π S (V/I) (Eq. 1)
Where, S refers to probe spacing in mm, I is the current in mA, V is denoted as potential
in mV. The conductivity of the samples was calculated by computing the value of ρ in the
following equation 2:
σ = 1/ ρ (Eq. 2)
Thermal study of the materials was done by using TGA (Perkin Elmer USA ana-
lyzer). Mass of each sample during analysis was in the range from 5-8 mg. An environ-
ment free of oxygen was provided to prevent any component of the sample from oxida-
tion. Temperature and weight measuring systems were calibrated. The samples were
closely connected to a thermocouple for the accurate measurement of temperature. Dur-
ing analysis sample was held for one minute at 30oC in the provided atmosphere and the
32
temperature was raised from 100-1000oC at the increasing rate of 20oC per minute. The
weight loss of the samples was determined from recorded TGA spectra keeping all other
parameters constant.
A.2.7 Electrochemical Characterizations
Electrochemical performance of the material and fabricated device was studied by
using ZRA Potentiostat/Galvanostat Reference 3000 (Fig. A.2.3).
Figure A.2.3: Electrochemical setup
Catalytic activity and redox processes of the synthesized PANI were investigated
by using cyclic voltammetry (CV) measurement at different scan rates within the poten-
tial ranging from -0.2 V to 0.8 V. The experiment was carried out in three electrodes sys-
tem using 1 M H2SO4 electrolyte, consisting gold sheet (working electrode on which sur-
face the material was coated), Ag/Ag chloride (reference electrode) and gold coil (coun-
ter electrode). For coating electrode, appropriate amount of powder sample was dissolved
in DMF and then 2mg of the active material was drop coated on working electrode. From
33
CVs curves, specific capacitance (Csp) of various PANI salts was calculated by using the
equation [110]:
𝐶𝑠𝑝 =𝐼
mv (𝐸𝑞. 3)
Where ‘I’ signify the current, ‘m’ depicts the mass of the active material and ‘v’ repre-
sents the scan rate. The active material loading is 2 mg/cm2 (dry weight).
Galvanostatic Charge/Discharge (GCD) measurement was done in a potential
ranging from -0.2 to 0.8 V at various current densities (1, 3, 5, 10, 15, 20, 30 and 40 Ag-
1), respectively. The experiment was performed in the same manner as discussed in CV,
using three electrode systems. From GCD curves, specific capacitance (Csp) of PANI salt
was calculated by using the equation [111]:
𝐶𝑠𝑝 =𝐼 × 𝛥𝑡
Δv × m (𝐸𝑞. 4)
Where, Csp designates specific capacitance (Fg-1), Δt is the time period of discharging
process in seconds (s), I refer to current (A), ΔV tells the potential window in volts (V),
m denotes mass of the electroactive material in gram.
The capacitive performance of fabricated device through GCD was checked in
two electrode system in which both ends of FTO electrodes of fabricated device were
clamped with the help of clips connected with the instrument. During the measurement,
the cell was hung upside down upon a beaker containing 1 M H2SO4 electrolyte solution
with the protruding filter paper dipped in the electrolyte for continuously providing the
electrolyte by the capillary action. The GCD measurement was performed under a poten-
34
tial window of -0.2-0.8 V at various current densities. The specific capacitance, energy
density and power density were calculated by using the equations [101]:
𝐶𝑠𝑝 = 2 ×𝐼 × ∆𝑡
∆𝑉 × 𝑚 (𝐸𝑞. 5)
Where factor 2 is due to the difference in capacitor configuration. Δt is the time period of
discharging process in seconds (s), I refer to current (A), ΔV tells the potential window in
volts (V), m denotes mass of the electroactive material in gram.
𝐸 (𝑊ℎ
𝐾𝑔) =
1
2𝐶𝑠𝑝∆𝑉2 ×
1000
3600 (𝐸𝑞. 6)
Where, E is energy density with unit of Wh/Kg, Csp designates specific capacitance (Fg-
1) obtained from Equation 5 and ΔV tells the potential window in volts (V).
𝑃 (𝑊
𝐾𝑔) =
𝐸
∆𝑡=
𝐼∆𝑉
2𝑚× 1000 (𝐸𝑞. 7)
P refers to power density having W/Kg unit, E is energy density obtained from
Equation 6, Δt is the time period of discharging process in seconds (s), I refer to current
(A), ΔV tells the potential window in volts (V), m denotes mass of the electroactive mate-
rial in gram.
Electrochemical Impedance Spectroscopy (EIS) was also used to characterize
electroactive materials for charge transfer resistance. During the EIS measurement the
frequency range was from 0.1-105 Hz at a potential of 0.2, 0.4, 0.6, 0.8, 1V.
35
Chapter A3
A.3 Results and Discussion
A.3.1 Polymerization of aniline
Chemical polymerization is a traditional technique used for the preparation of
PANI in bulk with large consumption of chemicals and longer time. Chemical polymeri-
zation is usually performed by slow addition of reactants one after another under vigor-
ous stirring. The product obtained is highly agglomerated and irregular shaped because of
heterogeneous nucleation. The key to obtain PANI fibers is to overcome the heterogene-
ous nucleation by rapid mixing.
For this, a facile, ultra-fast and green synthetic route is investigated by rapid mix-
ing of aniline with oxidant, APS, in acidic solution of novel dopant i-e phytic acid sodi-
um salt, by quick hand shaking, at room temperature. This allows the even distribution of
monomer and oxidant molecules before polymerization. When polymerization starts, the
oxidant rapidly polymerizes the monomers and induces the formation of nanofibers by
overcoming the heterogeneous nucleation. This, leads to the consumption of all the oxi-
dant and monomer molecules into the reproducible, inexpensive, scalable and highly
conductive and soluble PANI nanofibers with a high yield relative to other methods. Ad-
ditionally, polymerization time and the use of toxic chemicals is 99 % reduced in com-
parison with prior art (Table A.3.1).
36
Table 2: Comparison among already reported chemical, electrochemical methods with
the present method.
Method Solvent Route Equipment Yield Time for final product
Electrochemical
Organic/
Inorganic
Toxic
Cell development
Electrode,
Potentiostate
Very low More than 50 hours [112]
Chemical
Organic/
Inorganic
Toxic
Magnetic stirred,
Separatery
funnels
Low
More than 120 hours [113]
Present
(Rapid Mixing)
Water
Green
Don’t need
any of these
Excellent
5-10 minutes
A.3.2 Influence of Synthesis Parameters on the yield of PANI
The factorial experimental design is a powerful tool to realize the effects of some
independent variables that significantly affect the experimental results. Here we present
the results of the effect of monomer, oxidant and dopant on the yield of PANI.
A.3.2.1 Effect of Monomer Amount on Polymerization Yield
To investigate the effect of aniline amount on % yield of phytic acid sodium salt
doped PANI, the monomer amount was varied from 0.002-0.012 moles while that of oxi-
dant (0.0058 mole) and dopant (5 %) concentrations was maintained constant (Fig.A.3.1).
It was observed that the maximum yield can be obtained at 0.0055 mole of aniline. Fur-
ther increase in aniline amount decreases the % yield of polymer. This can be due to the
production of high amount of monomer’s active sites, which results into the generation of
37
oligomers. These oligomers are soluble in reaction medium. Furthermore, the fast de-
crease in oxidant’s efficiency can also be the reason for low yield [114].
Figure A.3.1: Effect of monomer amount on % yield of PANI.
A.3.2.2 Effect of Oxidant Amount on Polymerization Yield
The influence of oxidant amount on the yield of polymer was estimated by chang-
ing the amount of oxidant while keeping the amount of aniline and dopant same. The re-
sults are shown in Fig. A.3.2. From the figure it can be seen that the % yield of the poly-
mer first increases with increase of the oxidant amount from 0.0019 to 0.0078 mole.
However further increase in the oxidant amount leads to decrease in the % yield of the
product. This decrease at high oxidant amount might be due to the production of large
number of free radicles. This results in the shortening of the polymer chain and leads to
38
the production of oligomers, which are soluble in the reaction system. Therefore, low
yield of the product can be obtained [115]. On the other hand, low yield at less amount of
oxidant possibly be due to the formation of less number of free radicals in the reaction
mixture, resulting in lowering of yield [116].
Figure A.3.2: Effect of different amounts of oxidant on % yield of PANI.
A.3.2.3 Effect of Phytic acid sodium salt concentration on the yield of polymer
The preparation of phytic acid sodium salt doped PANI was done by changing the
dopant concentration and the effect on the yield of PANI salt is displayed in Figure A.3.3
and Table A.3.2. With increase in dopant concentration, the yield of PANI samples first
increases at its maximum and then go on decreasing with further addition of acid amount
as a dopant.
39
Figure A.3.3: % yield of PANI samples as a function of dopant concentration.
Table A.3.2: % yield of PANI samples.
Sample Code Dopant concentration (%)
(Wt/V) g / 100 ml
Yield (%)
P-0.5PA 0.5 80.73
P-1PA 1 86.59
P-3PA 3 93.00
P-5PA 5 98.62
P-7PA 7 89.00
P-10PA 10 83.17
Same trend is observed by Ayad and its coworker during the preparation of PANI
doped with H2SO4, HNO3, H3PO4 and CH3COOH. They reported that with increase in
dopant concentrations, there exists an increase in electrostatic repulsion within the PANI
40
chain. This repulsion led to the domination of the extended chain formation rather than
coiled resulted an increase in the yield [117]. Further increase in dopant amount results in
the hydrolysis of polymer chain which leads to reduction in the yield of PANI salts [118,
119].
Since we were interested to investigate the effect of phytic acid sodium salt (do-
pant) on the properties of PANI, therefore the samples synthesized on the basis of differ-
ent concentrations of dopant was selected for further study. Moreover, another reason for
samples selection is that excellent yield was obtained by changing dopant concentrations.
Various properties of the phytic acid sodium salt doped PANI samples were systematical-
ly investigated.
A.3.3 Fourier Transformed Infrared (FT-IR) spectroscopy
Fig. A.3.4 depicts the FTIR spectra of phytic acid sodium salt and various phytic acid so-
dium salt doped PANI samples. The FTIR spectrum of Phytic acid sodium salt display
basic absorption peaks. The characteristic bands at 1193 and 1087 cm−1 can be assigned
to the stretching vibration of P=O and P–O–C, respectively. The stretch at 554 cm-1 cor-
responded to the O–Na and O–P=O vibrations was observable at 2,402 [120]. The ab-
sorption peaks of OH group of water molecules present in the phytic acid sodium salt ap-
peared at 1642 and 1797 cm−1 [120].
While the FTIR spectra of various doped PANI samples shows the characteristic peaks at
1685 and 1558 cm-1 are attributed to the vibrations of CC in the quinoid and benzenoid
rings, respectively. The typical peak at 1487 is assigned to C-N stretching vibrations in
the neighborhood of the quinoid ring [121]. The absorptions at 1284 are cm-1 correspond
41
to the C-N bonds associated with the benzenoid ring. The absorption at 1104 cm-1 is due
to the CN bond associated with the quinoid ring. The peaks at 820 and 554 cm-1 are as-
sociated with P-O-C and O-NA stretching vibration in phytic acid sodium salt doped
PANI [122, 123]. The bands at 743 cm-1 represent C-H bending vibrations in the paradi-
substituted aromatic ring [123]. The peaks of CC and CN at1558 and 1104 respective-
ly are the characteristics peaks that suggest that PANI were transformed to the doped em-
eraldine salt state through the dopant phytic acid sodium salt, and the doping primarily
occurred at the quinoid ring segments [123, 124]. Furthermore, the broad absorption of
the CN at 1104 cm-1 in phytic acid sodium salt doped PANI also indicates electron de-
localization in the PANI backbone [124, 125]. Electron delocalization is the guarantee of
high conductivity of the acid doped emeraldine PANI salt, which is discussed in conduc-
tivity analysis section. Therefore the broad bands near 1108 in the doped PANI were as-
sumed be attributable to overlapping of the absorptions of the PANI skeleton and the
characteristic absorptions of P-O-C at 820 cm-1 and O-Na at 554 cm-1. Presence of the
bands attributed to the dopant ion and quinoid-benzenoid rings clearly specify the suc-
cessful synthesis of conducting salts of doped PANI and support the results of absorption
study (Fig. A.3.5).
42
Figure A.3.4: FTIR transmittance spectra of phytic acid sodium salt and phytic acid so-
dium salt doped PANI samples.
43
Table A.3.3: FTIR spectral absorption bands assignments of phytic acid sodium salt and phytic
acid sodium salt doped PANI samples.
S. No
Characteristics wavenumbers (cm-1) of various PANI salts
Assignment
Phytic acid
sodium salt
P-0.5PA
P-1PA
P-3PA
P-5PA
P-7PA
P-10PA
1 2402 --- --- --- --- --- --- stretching vibration of
O–P=O
2 1642 --- --- --- --- --- --- ν(O−H)
3 1797 --- --- --- --- --- --- ν (O-H)
4 1193 --- --- --- --- --- --- ν(P=O)
5 1087 --- --- --- --- --- --- ν(P–O–C)
6 554 --- --- --- --- --- --- ν(O–Na)
7 --- 1685 1682 1696 1696 1689 1689 ν (CC) Q
8 --- 1558 1566 1551 1566 1544 1558 ν (CC) B
9 --- 1487 1480 1480 1480 1480 1480 ν (C-N) Q
10 --- 1284 1288 1299 1292 1290 680 ν (C-N) B
11 --- 1104 1103 1104 1102 1101 570 ν (CN)
12 --- 820 821 822 820 822 821 ν (P-O-C)
13 743 745 745 744 743 745 β (CH)
14 554 554 554 554 554 554 ν(O−Na)
δ: in-plane defomation; B: benzoid; ν: stretching mode; Q: quinoid type ring; mode; :
bending mode; : out-of-plane deformation mode.
44
A.3.4 UV-spectroscopy analysis
Fig. A.3.5 shows a comparable shape with three absorption bands at about 344.89
nm, 424 nm and 786.59 nm. The band ranging from 344.89 to 349.15 nm can be attribut-
ed to the electronic π to π* conversions due to excitation of nitrogen in the benzenoid
rings. A shoulder at 424-427 nm credited to the polaron to π* transitions representing as-
similation of dopant in the polymer backbone [126, 127]. The band at infra-red region
ranging from 786.59 to 822 nm initiates from π - polaron transition (cationic species).
This broad band may be caused by interband charge transfer from benzenoid to quinoid
rings of conjugated PANI. Stronger absorption of this band signifies the protonation of
the synthesized PANI [128]. The wavelength, intensity and intensity ratios (A2/A1) of
A2 (second band) to the A1 (first band) of different amount of doped PANI are showed in
Table A.3.4. The values of A2/A1 for P-5PA is larger compared to others indicating the
high doping level than the others. It is well-known that lambda 2 exhibit a significant red
shift with increase in dopant concentration from P-0.5PA to P-5PA, signifying an in-
crease in conjugation length and ordered structure of PANI backbone. This may be due to
the fact that some prototype effects are produced by dopant ions which advance the or-
dering of PANI chains [129, 130]. Further increase in dopant amount from P-7PA to P-
10PA, a blue shift is detected. This blue shift might be due to the low degree of polymer-
ization or disordered structure of PANI because of fast polymerization rate [129].
45
Figure A.3.5: Absorbance spectra of various PANI samples.
Table A.3.4: The wavelength (λ) and intensity (A) derived from the UV-Vis spectra of
different PANI salts.
Sample A1 A2 λ 1 λ 2 A2/A1
P-0.5PA 0.286 0.354 343.11 819.69 1.237
P-1PA 0.503 0.675 347.23 726.59 1.341
P-3PA 0.370 0.508 346.68 797.57 1.372
P-5PA 0.829 1.173 349.15 822.01 1.415
P-7PA 0.484 0.588 345.58 813.50 1.215
P-10PA 0.529 0.618 344.89 792.76 1.168
46
A.3.5 X-Ray Diffractrometric analysis (XRD)
XRD examination was done to evaluate the molecular order with regard to crys-
tallinity, as charge transport in CP enhances by increasing molecular order. X-Ray scat-
tering patterns of different concentrations of phytic acid doped PANI samples are pre-
sented in Fig. A.3.6.
It can be noted that all the samples show similar XRD pattern with intense peaks
at 2θ= 17°, 20.5°, 23°, 26°, 29.6° and 30°. The peaks at 2θ= 17°, 23° and 29.6° are char-
acteristics of emeraldine salt state of PANI [131]. The peaks at 2θ= 20° and 2θ= 26° cor-
responds to the parallel and vertical periodic intervals of PANI chains/backbone, respec-
tively. The diffraction peaks observed at 26°, 29.6° and 30° reflects the aniline and do-
pant interaction during the polymerization and suggested incorporation of dopant into
polymer backbone [131].
XRD spectra illustrates that with the increase content of dopant from P-0.5PA to
P-5PA, the intensity of the diffraction peaks increases gradually. These intense peaks
count for the best structural ordering and hence may exhibit higher crystallinity [132].
Further increase in the dopant concentration, intensity of the peaks decreases as manifest-
ed in Fig. A.3.6, which results in the reduction of crystallinity.
From the XRD diffractogram of P-5PA, it is expected that all the peaks are very
intense comparatively to all other samples suggesting P-5PA has high ordering and regu-
larity in the backbone of the polymer. These properties are responsible for intermolecular
transport of the ionic species alongside the polymer chain and a little intermolecular hop-
ping owing to close and better packing of the material. Consequently, this high crystallin-
ity of the material leads to high conductivity and high electrocatalytic activity [133, 134].
47
Literature study reveals that by using commercial phytic acid solution as a dopant,
the similar behavior of XRD pattern is obtained with low crystallinity as for other report-
ed organic and inorganic acids doped PANI. Xiaohui Gao and its coworkers [84] investi-
gated comparison of undoped PANI, H3PO4 doped PANI and commercial phytic acid so-
lution doped PANI. They reported same XRD spectra with low crystallinity for both
doped PANI compared to undoped PANI. Santos et. al. [135] also reported the similar
behavior of XRD spectra with low crystallinity for H2SO4 doped PANI and commercial
phytic acid solution doped PANI.
In the present study, behavior of XRD pattern is different from those reported in
literature. Presence of high intense peaks reveals the high crystallinity of the prepared
material. Our ultra-fast oxidative method along with phytic acid sodium salt as a novel
dopant might be responsible for high crystallinity of PANI salts.
48
Figure A.3.6: XRD spectra of PANI samples.
A.3.6 Elemental composition and Elemental Mapping
To examine the elemental composition of phytic acid sodium salt doped PANI,
EDX analysis was employed and is presented in Fig A.3.7-A.3.12. EDX analysis shows
that PANI contains C, O, Na, N and P. The detection of Na and P in all the samples due
to the incorporation of novel dopant depicts the successful synthesis of PANI salts with
effective assimilation of the dopant in to the polymer backbone. The experimental results
revealed that increasing the ratio of dopant increased the Na and P contents in the salts up
49
to P-5PA. Further increasing the ratio of dopant decreases the contents of corresponding
elements.
The detected atomic ratios of sodium and phosphorus were respectively 0.11 %
and 0.39 % for P-0.5PA (Fig. A.3.7), 0.47 % and 0.55 % for P-1PA (Fig. A.3.8), 0.69 %
and 1.43 % for P-3PA (Fig. A.3.9), 1.05 % and 1.69 % for P-5PA (Fig. A.3.10), 0.97 %
and 0.98 % for P-7PA (Fig. A.3.11) and 0.89 % and 0.97 % for P-10PA (Fig. A.3.12).
EDX results clearly confirmed that all the samples are successfully doped and compari-
son of all the salts revealed that P-5PA salt manifests high percentages of Na and P as
high P content in doped PANI can successfully minimize the barrier height, and the con-
jugation in polymer chain creates a deep interaction for charge delocalization in intra and
inter-chain; and is expected to enhance electrical conductivity in P-5PA [84]. Thus the
incorporation of C, N, O, Na and P is also confirmed by EDX-elemental maps presented
in Fig. A.3.7-A.3.12.
50
Figure A.3.7: EDX and EDX-mapping of P-0.5PA.
51
Figure A.3.8: EDX and EDX-mapping of P-1PA.
52
Figure A.3.9: EDX and EDX-mapping of P-3PA.
53
Figure A.3.10: EDX and EDX-mapping of P-5PA.
54
Figure A.3.11: EDX and EDX-mapping of P-7PA.
55
Figure A.3.12: EDX and EDX-mapping of P-10PA.
56
A.3.7 Scanning Electron Microscopy (SEM)
Figures (A.3.13-A.3.15) display the SEM images of the as synthesized samples i-
e P-0.5PA, P-1PA, P-3PA, P-5PA, P-7PA and P-10PA both at low (a) and high (a*)
magnifications, respectively. From the analysis of SEM, approximately all the samples
showed nano fibrous morphology, and probability of formation of the nanofibers were
significantly enhanced with increase in dopant ratio (0.5 to 5% wt/v), while further in-
crease in the dopant concentration up to 10% wt/v the fibers become thick, shorter and
agglomeration take place. An evolution from dense agglomerated short fibrous morphol-
ogy for P-0.5PA (Fig. A.3.13a) and P-1PA (Fig. A.3.13b) to interconnected cauliflower-
like morphology with some branched fibers with diameter of 91 nm to 162 nm along with
some flakes is clearly noted by increasing the dopant concentration from 0.5 to 3 % wt/v
(Fig. A.3.14a). Further increase in the dopant ratio, many long rods like interconnected
structure with rough and porous morphology is observed in P-5PA (Fig. A.3.14b) having
diameter range of 69 nm to 129 nm, comparatively less than P-3PA. Further increase in
dopant concentration results thicker and shorten fibers, although rough and porous with
diameter range of 182 nm to 276 nm in case of P-7PA (Fig. A.3.15a). These thick and
short fibers agglomerated when dopant ratio increases from 7 % to 10 % Wt/v in P-10PA
(Fig. A.3.15b).
On comparison of P-5PA with P-3PA and P-7 PA, cauliflowers like morphology
of P-3PA showed that rod like fibers comes out from the flakes and are agglomerated at
one center. This might be due to the dominancy of coiled chains formation in P-3PA.
This type of structure is not feasible for energy storage applications as presence of flakes
reduces the diffusion of electrolyte into the polymer matrix which in turn decreases the
57
catalytic activity of the material [136, 137]. In case of P-7PA, breakage of long fibers in
to small pieces is clearly seen with increase in diameter of fibers. This in turn reduces the
electrical properties of the material [138]. The most desirable morphology-type with po-
rosity was noted to evolve just around P-5PA, exhibits rough, porous network like fibrous
nanostructure with distinct connectivity and particle size distribution. This gives P-5PA
an interesting desirable structure that is absent in the other cases.
The ultra-fast and facile synthesis route due to multi-phosphate structure of Phytic
acid sodium salt provides a useful method to bulk preparation of porous and fibrous
nanostructures of PANI. As it is well-known, that such interconnected PANI nanofiber
structures can be beneficial for electrical and capacitive properties than wires and parti-
cles when used as electrode materials for supercapacitors. This can be due to large open
channels of the pores with rough surface within the structures [139] as fibrous and rough
feature of PANI provides high surface area that is favorable for the transport of electrons
and ions and is beneficial for good electrocatalytic properties [82].
.
58
Figure A.3.13: Surface morphology of a) P-0.5PA, (a*) zoomed image of P-0.5PA and
(b) P-1PA, (b*) zoomed image of P-1PA.
59
Figure A.3.14: Surface morphology of a) P-3PA, (a*) zoomed image of P-3PA
and (b) P-5PA, (b*) zoomed image of P-5PA.
60
Figure A.3.15: Surface morphology of a) P-7PA, (a*) zoomed image of P-7PA
and (b) P-10PA, (b*) zoomed image of P-10PA.
61
A.3.8 DC Conductivity
DC conductivity of PANI pellets was determined by four probe method. Conduc-
tivity measurements results of the samples (P-0.5PA-P-10PA) are displayed in Fig.
A.3.16 and listed in Table A.3.5. Conductivity results illustrate that conductivity first in-
crease with increase in dopant concentration while further increase of the dopant concen-
tration results in the decrease of conductivity. From the Table A.3.5 the highest conduc-
tivity is 10 S/cm for P-5PA which is the most optimized case.
Pan et al. [82] synthesized phytic acid doped PANI hydrogels with electrical con-
ductivity of 0.11 S/cm by using commercial phytic acid solution. Gawli et.al. [78], re-
ported simultaneous doping of HCl and phytic acid solution in to the PANI and found
high supercapacitive performance by using synthesized material. They also reported the
conductivity of PANI-HCl, PANI-PhA and P-MIX as 0.48, 0.32, 0.61 S cm−1, respective-
ly. Xiaohui Gao and its coworkers [84] synthesized phosphorized PANI by using com-
mercial phytic acid solution as dopant and reported conductivity was 0.28 S/cm.
It is obvious from the reported literature that the value of conductivity of phytic
acid sodium salt doped PANI is higher in magnitude than that of commercial phytic acid
solution doped PANI and other acids doped PANI [140, 141, 142]. From the above dis-
cussion, it could be revealed that phytic acid sodium salt can efficiently enhance the con-
ductivity of as synthesized material than other dopants because it offers the optimum
acidic environment for the preparation and go into the polymer chain in the form of pro-
ton acid. This conductivity is high enough for being used as an electroactive electrode
material in electronic devices. This outcome might be due to well electron delocalization
62
in the conjugated polymer, which is protracted by the formation of nanoscale fibrous
cross-linked network after using phytic acid sodium salt as a dopant. The different con-
ductivities of PANI salts can be revealed by EDX analysis as high doping level in P-5PA
results in the reduction of barrier height and higher extent of interchain interactions. This
is responsible for enhancement of electrical conductivity [143].
Figure A.3.16: Effect of dopant concentration on conductivity.
Table A.3.5: Four probe conductivity results of PANI samples.
Sample Code Dopant concentration (%)
(Wt/V) g/100ml
Conductivity
(S/cm)
P-0.5PA 0.5 1.37
P-1PA 1 3.62
P-3PA 3 5.44
P-5PA 5 10.00
P-7PA 7 5.11
63
P-10PA 10 3.50
A.3.9 Thermo Gravimetric Analyses (TGA)
The thermal stability of PANI salts was explored by the TGA measurement in the
range of 50-800 oC, in N2 atmosphere. The TGA curves clearly displayed three steps
weight loss. The first weight loss is owing to the moisture evaporation such as water. The
second step weight loss is ascribed to the de-doping and decomposition of the dopant.
The weight loss at third and final step is mainly due to the thermal decomposition of
PANI backbone [144].
Fig. A.3.17 displays the thermal profile of various concentrations of phytic acid
sodium salt doped PANI salts with three step degradation process (illustrated in Table
A.3.6). From the Figure and tabulated results, it is clear that thermal stability of PANI in-
creases up to P-5PA (670 oC) with increase in dopant concentration followed by decrease
in stability from P-7PA (624 oC) to P-10PA (614 oC) with further increase in dopant con-
tent.
It can be demonstrated that high thermal stability of P-5PA might be due to the
nano fibrous cross-linked particles in which the PANI chains are entangled between the
dopant and deprotonated imine of PANI Chains. Since the thermal decomposition of
phytate groups occur at about 550 oC, therefore the decomposition of doped PANI back-
bone at 614-670 oC is plausible [145].
64
Figure A.3.17: Thermal profile of PANI samples.
65
Table A.3.6: Temperature range and weight loss of first, second and third stages
of various PANI samples.
Sample Code Temperature Range (oC) % Weight Loss
P-0.5PA
24-78 8
248-330 44
330-623 33
P-1PA 34-64 7
233-327 44
327-648 43
P-3PA
25-82 7
244-326 39
326-663 44
P-5PA
24-62 5
231-326 44
326-670 45
P-7PA
35-86 5
239-326 41
326-624 47
P-10PA
37-88 4
230-332 41
332-614 44
66
A.3.10 Solution Processibility of Phytic acid sodium salt doped PANI
Synthesis of PANI through the traditional chemical oxidative polymerization re-
sults in the formation of highly agglomerated particles which are difficult to disperse and
hence reduces its processability in various fields. Conventional techniques for making
soluble or dispersible PANI includes copolymerization, chemical functionalization, sur-
factants assistant emulsion or dispersion polymerizations, but all encompass trade-offs
regarding conductivity, cost, purity or scalability [141, 146, 147, 148].
The successful synthesis of PANI nanofibers has authorized us to develop a cost
effective and suitable strategy for the improvement of PANI processability. Nanostruc-
tured PANI fibers synthesized through the present technique are soluble in DMSO, DMF,
NMP, THF, ethanol and more surprisingly in water, which permits the use of facile and
cost-effective technique to process this synthesized nanostructure material into a variety
of utilizable forms like films and composites.
The solubility of PANI in water broadens its application in electro-optical fields
such as electrochromics [149], actuators [150], corrosion protection [151], supercapaci-
tors [152] etc. and biological fields such as biological sensors [153], regenerative medi-
cines, tissue engineering [154] etc. The solubility in water might be due to the strong af-
finity of the dopant portion of the polymer towards water. Table A.3.7 lists the solubility
of PANI in the above-mentioned solvents. Its solubility in water is highest (9.5g/100ml),
while in NMP, DMF, DMSO, THF and ethanol exceeds 6 g/100 ml. This indicates that
the prepared PANI salt has good solubility in common polar solvents. Its solution can be
67
drop coated or spin coated on appropriate substrates (Fig. A.3.18), for desirable applica-
tions.
Figure A.3.18: Film of water soluble PANI on glass slide.
All these solvents are chemically different from each other. It is well understood
that the solubility of PANI salt is affected by interaction among the PANI chain, counter
ions as well as by the solvent. Therefore, differences in maximum solubility of phytic ac-
id sodium salt doped PANI in the above solvents were expected. Although polar solvents
make effective interaction with the PANI chain through protonation or the formation of
hydrogen bond [155]. From literature it is clear; this type dissolution of PANI is possible
only when monomer and dopant exist in a good proportion in the synthesized sample
[156]. Therefore, it can be assumed that the dissolution of phytic acid sodium salt doped
PANI in the above polar solvent is due to the existence of the fine proportion of both the
monomers and the dopant in the synthesized sample.
68
Table A.3.7: Solubility of PANI salt (P-5PA) in different solvents (g/100 ml).
Solvent NMP DMF DMSO THF H2O Ethanol
Solubility 8.15 8.72 7.52 8.45 9.50 6.3
A.3.11 Cyclic voltammetry (CV)
To investigate the dopant influence on the electrocatalytic efficiency and capaci-
tive energy storage behaviors of the PANI salts, the electrochemical properties of the syn-
thesized samples (P-0.5PA, P-1PA, P-3PA, P-5PA, P-7PA and P-10PA) as electrodes in
supercapacitors were tested by cyclic voltammetry (Fig. A.3.19-Fig. A.3.25). These
curves were also used to calculate specific capacitance (Csp) of these various electrode
materials at different scan rates by using equation 3 mentioned in experimental section.
The compared CV profile of the PANI electrodes (P-0.5PA, P-1PA, P-3PA, P-
5PA, P-7PA and P-10PA) were recorded at lower scan rate (20 mV) and are depicted in
Fig. A.3.19. All the PANI salts depicted a quasi-rectangular shaped CV curves with two
pairs of redox peaks that are attributable to the conversion of leucomeraldine to emerald-
ine form and faradic emeraldine to pernigraniline form of PANI demonstrated that energy
storage mechanism is a Faradaic reaction [157]. Shapes of the CV curves suggested good
capacitive nature of PANI and mainly contributes by double layer capacitance and pseu-
do capacitance with a feature of redox pairs [158]. It can be seen that among different
samples of PANI salts, P-5PA exhibits a significantly high current, suggesting its strong
interaction with the dopant molecule. Such interaction results in high porosity and rough
surface, providing larger electrode/electrolyte interface area for more redox reactions [85,
159].
69
Furthermore, larger integrated area of P-5PA electrode is shown which possibly
be due to the cross linked nano fibrous and porous morphology. This suggests the fast
rate of ionic transport and hence high capacitance [159].
The Csp calculated from the curves (at low scan rate) are displayed in Table
A.3.8 and histogram (Fig. A.3.20). The obtained results show that P-5PA (Fig. A.3.19)
displays higher value of Csp (950 ±1.091 Fg-1) in comparison with P-0.5PA (582.5±
2.056 Fg-1), P-1PA (819.75± 1.805 Fg-1), P-3PA (875± 1.545 Fg-1), P-7PA (840± 1.945
Fg-1) and P-10PA (738.95± 2.243 Fg-1).
Figure A.3.19: CV curves of various PANI films at scan rate of 20 mV/s in 1 M
H2SO4 solution.
70
Table A.3.8: Anodic peak current (Ipa), cathodic peak current (Ipc) and specific capaci-
tance (Csp) with standard error of various PANI samples at scan rate of 20 mV/s.
Sample
Code
Ipa Ipc Csp (Fg-1) Standard
error
P-0.5PA 23.3 -22.45 582.5 ± 2.056
P-1PA 32.8 -21.08 819.75 ± 1.805
P-3PA 35.0 -26.81 875 ± 1.545
P-5PA 39.0 -30.28 950 ± 1.091
P-7PA 33.6 -26.99 840 ± 1.945
P-10PA 29.56 -18.97 738.95 ± 2.243
Figure A.3.20: Histogram showing Csp with error bars of various samples of PANI at
scan rate of 20 mV/s in 1 M H2SO4 solution.
71
These samples are further tested by subjecting to higher scan rate of 300 mV and
obtained curves are displayed in Fig. A.3.21 and the Csp values are given in the form of
table (table A.3.9) and histogram (Fig. A.3.22). It can be observed form the CV curves
that nearly rectangular shape of all the samples are maintained even at higher scan rate
which depicts its excellent electrochemical performance. Shifting of anodic peaks to-
wards positive potential is obvious because at high scan rate, there is an enhancement of
ohmic resistance which makes diffusion of ions into the inner surface of electrode mate-
rial difficult and is expected to peak shifting [160, 161]. Additionally, low Csp is ob-
served for all the samples and the trend of Cs at low scan rate is maintained at higher scan
rate. P-5PA shows the highest Csp value of 517.5± 1.520 Fg-1 relative to all other sam-
ples i.e P-0.5PA (300.5± 2.376 Fg-1), P-1PA (378.66± 2.095 Fg-1) P-3PA (454.17± 1.617
Fg-1), P-7PA (424.16± 1.962 Fg-1) and P-10PA (372.67± 2.053 Fg-1).
72
Figure A.3.21: CV curves of various PANI films at scan rate of 300 mV/s in 1 M
H2SO4 solution.
Table A.3.9: Anodic peak current (Ipa), cathodic peak current (Ipc) and specific ca-
pacitance (Csp) with standar error of various PANI samples at scan rate of 300 mV/s
Sample Code Ipa Ipc Csp (Fg-1) Standard error
P-0.5PA 182.34 -124.8 300.5 ± 2.376
P-1PA 225.95 -168.41 378.66 ± 2.095
P-3PA 274.15 -203.6 454.17 ± 1.617
P-5PA 309.34 -238.79 517.5 ± 1.520
P-7PA 252.34 -183.71 424.16 ± 1.962
P-10PA 221.74 -140.1 372.67 ± 2.053
73
Figure A.3.22: Histogram showing Csp with error bars of various PANI samples at scan
rate of 300 mV/s in 1 M H2SO4 solution.
From the Table A.3.8 and A.3.9, it can be observed that capacitance is inversely
related to scan rate as all the samples shows high Csp values at low scan rate than at high
scan rate. It is believed that slow scan rate can permit electrolyte to easily enter into the
pores of the active material and interacts with the electrode inner surface and leads to
large storage of charge on the electrode surface, hence provide high capacitance. Whereas
at higher scan rate, the ineffective interaction occurs between the electrode and electro-
74
lyte due to diffusion limitation, results less storage of charge at the surface of electrode,
hence low capacitance is observed [161].
Above observation demonstrated that P-5PA exhibits the highest specific capaci-
tance both at lower and higher scan rate. The superior capacitive performance attained by
our synthesized material endorses the distinctive advantages of the rough, porous inter-
connected nanostructures and phytic acid sodium salt crosslinked PANI material.
The capacitance behavior of P-5PA electrode is further explored by recording the
CV curves at a wide range of scan rates (20, 50, 100, 150, 200, 250 and 300 mV). The
cyclic voltammograms of P-5PA are shown in Fg. A.3.23 and the calculated values of
Csp are presented both in tabulated form (Table A.3.10) and histogram (Fig. A.3.24). It
is notable that P-5PA performs excellent electrochemical behavior even in a wide range
of scan rates. The CV curves of P-5PA electrode are quite stable and reflect no aberration
even at high scan rates suggesting that the synthesized material is highly stable with re-
spect to charge transfer [82, 159]. Furthermore, the values of Csp of electrode material
decreases with increase in scan rates which is consistent with the above discussed results.
The redox processes take place on the electrode are either kinetically controlled or
diffusion controlled. To check this property, a graph is plotted between current density
and (scan rate) ½
(Fig. A.3.25). The obtained linear relationship implies that the redox
reaction is diffusion controlled within the range of 20-300 mV s−1, suggesting the good
rate capability of the electrode [162].
The behavior of material at different scan rates is also important for observation
of its high-power characteristics which is also an important property of a material for its
75
successful application in different technologies involving supercapacitors. The increase in
current densities with scanning rates (Fig. A.3.25) illustrated the excellent stability, re-
versibility and quick response to redox processes [162]. These outcomes revealed a high-
power delivery of the PANI materials as electroactive electrode materials in supercapaci-
tors applications. The enhancement in the electrochemical properties originates from the
highly percolative electron conduction pathway and is expected due to our ultra-fast syn-
thetic route by using phytic acid sodium salt as a novel dopant.
Figure A.3.23: CV curves of P-5PA film at various scan rates in 1 M H2SO4 solution.
76
Table A.3.10: Anodic peak current (Ipa), cathodic peak current (Ipc) and specific capac-
itance (Csp) with standard error of P-5PA at various scan rates.
Scan Rate (mV) Ipa Ipc Csp (Fg-1) Standard
error
20 46.21 -28.34 950 ± 1.091
50 95.3 -63.56 870 ± 1.171
100 152.8 -108.7 766.35 ± 1.120
150 190.3 -146 655.33 ± 1.247
200 236.5 -179.3 590.92 ± 1.317
250 273.7 -208.7 548.72 ± 1.476
300 309.1 -238.8 517.5 1.520
Figure A.3.24: Histogram showing Csp with error bars of P-5PA at scan rates of 20, 50,
100, 150, 200, 250 and 300 mV/s.
77
Figure A.3.25: Relation of cathodic and anodic peaks of P-5PA against (scan rate)1/2.
A.3.12 Galvanostatic Charge/Discharge (GCD) Using Three Electrode System
Further exploration of the capacitive behavior of the as prepared PANI electrodes
was achieved by employing the galvanostatic charge/discharge measurement in three
electrode system within a potential range of -0.2 to 0.8 V. Fig. A.3.26 depicts the GCD
curves taken at 1 Ag-1 (low current density) for all samples. All the GCD curves of the
PANI salts displayed nearly symmetric and equilateral triangular shapes, which are char-
acteristic of excellent capacitance and high reversibility of PANI salts during charg-
ing/discharging process [163]. The deviation of discharge curves from a linear shape is an
evident of pseudo capacitance behavior due to the quick response of redox processes
[158, 164]. Longer time of discharging process is observed at low current density possi-
bly because of enough inclusion or discharge of counter anions during the process [163].
78
The Csp values for all these samples were calculated by using equation 4 and are illus-
trated in the Table A.3.11 and Figure A.3.27.
Results concluded that the high value of Csp is depicted just around P-5PA i-e
832.5± 1.400 F g−1 relative to P-0.5PA (462.9± 2.390 F g−1), P-1PA (500.5± 2.224 F
g−1), P-3PA (676.5± 1.868 F g−1), P-7PA (535± 1.962 F g−1) and P- 10PA (460± 2.634 F
g−1). The synergistic effect of the dopant in PANI matrix leads to the formation of con-
ductive, rough and porous network like nanostructure, responsible for high Csp value in
P-5PA.
Figure A.3.26: GCD curves of various PANI samples at 1 Ag-1.
79
Table A.3.11: Csp values with standard error of PANI different samples against low cur-
rent density of 1 Ag-1.
S. No. Sample Code Current Density (Ag-1) Csp (Fg-1) Standard
error
1 P-0.5PA 1 462.9 ± 2.390
2 P-1PA 1 500.5 ± 2.224
3 P-3PA 1 676.5 ± 1.868
4 P-5PA 1 832.5 ± 1.400
5 P-7PA 1 535 ± 1.962
6 P-10PA 1 460 ± 2.634
Figure A.3.27: Histogram of Csp with error bars of different PANI samples at 1Ag-1.
80
The GCD test for all samples was also carried out at a higher current density of 40
Ag-1. The obtained plots are shown in Fig. A.3.28 and the calculated values of Csp are
shown in table A.3.12 and Fig. A.3.29. The order of specific capacitance found is, P-0.5
PA < P-1PA < P-3PA < P-10 PA < P-7 PA < P-5PA. It is manifested that the same trend
of Csp observed for all samples at 1 Ag−1 is maintained here also, indicating the robust-
ness of the as-prepared phytic acid sodium salt doped PANI as electrode materials [163].
P-5PA reflects the highest Csp value of 528± 1.357 Fg−1 in comparison to all other sam-
ples i.e P-0.5PA (272± 2.468 F g−1), P-1PA (334.45± 2.301 Fg-1), P-3PA (438.65± 2.067
F g−1), P-7PA (363.35± 2.624 F g−1) and P-10PA (322± 2.755 F g−1), respectively.
Figure A.3.28: GCD curves of various PANI samples at 40 Ag-1.
81
Table A.3.12: Csp values with standard error of different PANI samples against high
current density of 40 Ag-1.
S. No Sample Code Current Density (Ag-1) Csp (Fg-1) Standard
error
1 P-0.5PA 40 272 ± 2.468
2 P-1PA 40 334.45 ± 2.301
3 P-3PA 40 438.65 ± 2.067
4 P-5PA 40 528 ± 1.357
5 P-7PA 40 363.35 ± 2.624
6 P-10PA 40 322 ± 2.755
Figure A.3.29: Histogram of Csp with error bars of different PANI samples at 40 Ag-1.
82
Observations of the above findings revealed that high Csp values are obtained at
low current density of GCD and vice versa. This can be attributed due to the sufficient
diffusion of counter-anions into and out of PANI during the process of charg-
ing/discharging at the lower current density while high current density contributes to the
increase in the ohmic resistance which results slow diffusion of ions by resisting the elec-
trolyte ion to penetrate the inner surface of active materials [165]. This process is similar
to that observed in CV analysis.
Due to comparatively higher values of Csp both at low and high current densities,
the possibility of P-5PA electrode as the potential application of capacitor is higher than
others. Therefore P-5PA was subjected to a wide range of current densities ranging from
(1 Ag−1 to 40 Ag−1) and is plotted in Fig. A.3.30 and the values of specific capacitance
are displayed (Table A.3.13 and Fig. A.3.30). Tabulated results indicates that at low cur-
rent density of 1 A g−1, P-5PA electrode shows maximum value of Csp i-e 832.5± 1.400
F g−1 and this remains 528± 1.357 F g−1 when the current density was increased to 40 A
g−1, suggesting that this P-5PA electrode can retain 67.64% of its initial Csp when the
current density is almost 39 times higher than the initial value. The Csp value of P-5PA
electrode is found to be much better than the values as reported for other PANI and PANI
based materials for supercapacitors mentioned in Table A.3.14.
The excellent capacitive performance of P-5PA electrode can mainly be attributed
to the nanofibrous, porous and rough surface of the electrode material where the phytic
acid sodium salt anchored PANI surface that can effectively accumulate the ions of elec-
trolyte and also facilitates the transportation of ions to the inner surface of the electrode
by decreasing ion diffusion path even at higher current density. From these finding, we
83
can say that our material has the potential for application in electrochemical supercapaci-
tors.
Figure A.3.30: GCD curves of P-5PA at current densities of 1, 3. 5, 10, 15, 20, 30 and
40 Ag-1.
84
Table A.3.13: Csp values with standard error of P-5PA against a wide range of current
densities.
S. No. Current Density (Ag-1) Csp (Fg-1) Standard
error
1 1 832.5 ± 1.400
2 3 706.5 ± 1.496
3 5 645.5 ± 1.473
4 10 597 ± 1.592
5 20 573 ± 1.513
6 30 556 ± 1.579
7 40 528 ± 1.357
Figure A.3.31: Histogram of Csp with error bars of P-5PA at various current densities.
85
Table A.3.14: Comparison of the Specific Capacitance of our synthesized PANI with re-
ported PANI and PANI based materials in three electrode system.
Materials Current
Density
Capacitance Electrolyte Year References
Crosslinked PAni 1 Ag−1 297 Fg−1 1 M H2SO4 2014 [143]
G/PANI 1 Ag−1 436 Fg−1 2 M H2SO4 2015 [166]
PAni @MnO2/graphene 4 Ag−1 695 Fg−1 1 M Na2SO4 2016 [163]
Polyaniline graphene hy-
drogel
2 Ag-1 710 Fg-1 1 M H2SO4 [167]
PAni- H2SO4
0.5 Ag−1 333 Fg−1
1 M H2SO4 2016 [132]
PANI/GO 20 Ag−1 447.5 Fg−1
1 M H2SO4 2016 [132]
Nylon 6,6/ PAni 10 Ag−1 309 Fg−1 1 M H2SO4 2016 [168]
PAni -rGO nanocomposite 20 Ag−1 546 Fg−1 1 M H2SO4 2017 [169]
Graphene/PAni compo-
sites
1 Ag−1 752 Fg−1 1 M H2SO4 2018 [170]
PANI 0.5 Ag−1 341 Fg-1 1M H2SO4 2018 [171]
Cl-PAni NFs 30 Ag−1 105 Fg−1 0.1 M HCl 2019 [85]
PhA-PAni NFs 30 Ag−1 227 Fg−1 0.1 M HCl 2019 [85]
PANI 0.5 Ag−1 712 Fg-1 1M H2SO4 2019 [172]
Carbon coated PANI 1 Ag−1 783 Fg-1 1M H2SO4 2019 [173]
Honycomb like PANI 1 Ag−1 480 Fg-1 1M H2SO4 2019 [174]
PANI-Carbon cloth 25mAcm-2 438 Fg-1 1M H2SO4 2019 [175]
Phytic acid sodium salt
doped PAni
1 Ag−1
40 Ag−1
832.5±1.400Fg−1
528 ± 1.357 Fg−1
1 M H2SO4
Present
86
A.3.13 Rate Capability
Rate capability of the electrode materials is an essential parameter to design high
rate supercapacitors for fast charging/discharging application. In view of this, for GCD
measurement we subject the most optimized case P-5PA for a wide range of current den-
sities ranging from 1 Ag-1 to 40 Ag-1. The individual charging and discharge time cures
for P-5PA are shown in Fig. A.3.32. In this wide range of current densities, this electrode
material yielded excellent rate performance. 67.64 % of capacitance retention was ob-
served from 1 Ag−1 to 40 Ag−1 suggesting an anomalous rate competence at such a wide
and high current density. This shows a profound distinction to formerly stated PANI-
based electrodes, where 25–40% losses in capacitance value was observed at current den-
sity from 1-5 Ag-1 [175, 176]. This high performance could be attributed to the facile ion-
ic and electronic transport emanating from the conductive network of the prepared PANI
salt.
Figure A.3.32: Percent capacitance retention of P-5PA against various current densities.
87
A.3.14 Cycling stability
Cycling stability is also a key factor for the operational supercapacitors. Superca-
pacitors based on CPs often experienced limited cyclability because of shrinking and
swelling of electroactive polymers during its charging/discharging operation [177]. The
cycling performance of P-5PA depicted capacitance retention of ∼95.26 % over 1,000
cycles at a high current density of 40 Ag−1 (Fig. A.3.33). According to the reported litera-
ture, this % retention is superior to the supercapacitors based on PANI (typically 60 ∼
85% retention for 1,000 cycles) [175, 178]. The achievement of high cycling perfor-
mance for our electrode material could be attributed to the porous and crosslinked nano
fibrous morphology of phytic acid sodium salt doped PAni that can compensate the
shrinking and swelling problems of the polymer network during intensive cycling pro-
cesses.
Figure A.3.33: Cycle stability of P-5PA over 1,000 GCD cycles at 40 Ag−1 while inset
reflects few GCD cycles at 40 Ag−1 current density.
88
A.3.15 Electrochemical Impedance Spectroscopy (EIS)
To evaluate the interfacial charge transfer process at electrode/electrolyte inter-
face, All PANI electrodes were subjected to EIS analysis and the corresponding Nyquist
plots are depicted in Fig. A.3.34 at open circuit voltage within 0.1–105 Hz frequency
range. Each spectrum manifests a semicircle that appears in region of high frequency and
an inclined line observed in the region of low frequency. Surface properties of the elec-
trode are associated with the semicircle as high frequency region involves the electro-
chemical process at the electrode surface and is responsible for the faradic charge transfer
resistance (Rct) and double layer capacitance. The inclined line at low frequency region
depicts the transport and diffusion of the ions due to pseudocapacitance [158]. The ap-
pearance of a vertical line supports the capacitive behavior of the material. If inclined line
is short and close to the y-axis, it is attributed to the ideal capacitive behavior [131, 179].
It can be seen from the Fig. A.3.34, that the line of P-5PA is shorter in length and
collapse more towards the Z”-axis relative to others. This suggests good capacitive be-
havior of P-5PA electrode.
89
Figure: A.3.34: Impedance spectra of various PANI samples at open circuit voltage.
Based on the above results, P-5PA electrode was further studied at different volt-
ages (Fig. A.3.35-A.3.37) and the corresponded Nyquist plots were fitted with the pro-
posed equivalent circuit model depicted in Fig. A.3.38 by using Echem Analyst which
gives different impedance parameters (listed in Table A.3.15). The proposed equivalent
model includes Rs (solution resistance), Rct (charge transfer resistance), CPE1 (double-
layer capacitance at the electrode/electrolyte interface), and CPE2 (pseudocapacitance
due to the conducting phytic acid sodium salt doped PANI material) [158]. A decreasing
trend of Rct is observed from 8.265 Ω at 0.2 V to 7.439 Ω at 0.6 V followed by an in-
crease in value of Rct from 7.490 Ω and 8.571 Ω at 0.8 V and 1 V, respectively. Same
90
trend is seen for the value of (n) which increases up to 0.769 Ω at 0.6 V and then de-
creases to 0.657 Ω at 1 V. These values illustrated a significant effect on the inclined line
that gradually shifted towards y-axis with the increase in potential from 0.2 to 0.6 V. but
at high voltages i-e from 0.8 V to 1 V, this inclined line move apart from y-axis.
It is reported that on increasing potential up to the certain limit, an increase in
pseudocapacitive behavior of the electrode material is observed [110, 180]. Same obser-
vations can be seen in the present work, when we increase the potential from 0.2 to 0.6 V,
the plots show dominant pseudocapacitive behavior but after 0.6 V, the decrease in pseu-
docapacitive behavior is observed from 0.8-1 V. This demonstrates that synthesizing
PANI nanofibers by ultra-fast and green route is a significant and simple way to improve
electrochemical properties. The phytic acid sodium salt doped PAni nanofibers may have
potential applications in energy storage and other electrochemical devices.
91
Figure A.3.35: Impedance spectra of P-5PA a) at 0.2 V and b) at 0.4 V.
92
Figure A.3.36: Impedance spectra of P-5PA a) at 0.6 V and b) at 0.8 V.
93
Figure A.3.37: Impedance spectra of P-5PA at 1 V.
Figure A.3.38: Proposed equivalent circuit for P-5PA film.
94
Table A.3.15: Parameters derived from impedance spectra of P-5PA at different voltag-
es.
Voltage (V) Rct (ohm) Rs (ohm) CPE 1 CPE 2 n
0.2 8.265 4.38 × 10-1 1.27× 10−3 1.61× 10−2 0.636
0.4 7.674 4.24 × 10−1 2.33× 10−3 1.56 × 10−2 0.736
0.6 7.439 2.81 × 10−1 8.04 × 10−4 2.69 × 10−2 0.769
0.8 7.490 3.54 × 10−1 2.68 × 10−4 2.69 × 10−2 0.708
1 8.571 3.60 × 10−1 3.08 × 10−4 2.22 × 10−2 0.657
A.3.16 Fabrication of Symmetric Supercapacitor Device
Utilizing the most optimized sample i.e. P-5PA as the electrodes in a symmetric
configuration for practical application, we tested this material in two electrode system at
various charging/discharging current densities ranging from 1 Ag-1 to 40 Ag-1 (Fig.
A.3.39). From the discharging time curves the respective specific capacitance values of
the material for these different current densities were calculated Table A.3.16. The spe-
cific capacitance obtained from the symmetric supercapacitor is lower than those meas-
ured in the three-electrode system and decrease with the increase of current density,
which is reasonable due to the difference in capacitor configuration [178]. For 1 Ag-1 the
specific capacitance is 531.5 ±2.177Fg-1 and gradually decreases to 355.35 ±2.195Fg-1 at
40 Ag-1, indicating a total loss of 176.15 Fg-1. However, the specific capacitance values
95
vary very little in such a broad range of current densities and this is very important point
of appreciation of the material [78, 159].
0 400 800 1200 16000.0
0.2
0.4
0.6
0.8
Pot
enti
al (
V)
Time (s)
1 A/g
3 A/g
5 A/g
10 A/g
20 A/g
30 A/g
40 A/g
P-5PA
Figure A.3.39: GCD curves of PANI based symmetric device at current densities of 1, 3,
5, 10, 20, 30 and 40 Ag-1.
96
Table A.3.16: Csp values with standard errors, Energy Density and Power Density of
PANI based symmetric device against a wide range of current densities.
S.No Current Density
(Ag-1)
Specific Capacitance
(Fg-1)
Energy Density
(W h Kg-1)
Power Density
(W Kg-1)
1 1 531.5 ± 2.177 73.82 500
2 3 455.25 ± 2.049 63.23 1500
3 5 413.8 ± 1.992 57.47 2500
4 10 397.45 ± 2.310 55.20 5000
5 20 384.95 ± 2.104 53.46 10,000
6 30 377.2 ± 2.007 52.38 15,000
7 40 355.35 ± 2.195 49.35 20,000
In this wide range of current densities, the material almost shows 66.86 % reten-
tion in the specific capacitance (Fig. A.3.40). This excellent specific capacitance and
good rate performance of the material is much better than previous reports for PANI and
PANI based materials. Comparison with literature is given in the Table A.3.17.
Figure A.3.40: Percent capacitance retention of PANI based symmetric device against
various current densities.
97
Table A.3.17: Comparision of the Specific Capacitance of the present synthesized PANI
with reported PANI based materials in two electrode system.
Material Current
Density
Capacitance Electrolyte Year Reference
3 D PAni Architecher 40 Ag-1 350 Fg-1 1 M H2SO2 2016 [78]
Pani/Graphene 0.5 Ag-1 447 Fg-1 1 M H2SO4 2018 [178]
PAni/grapheme com-
posite
2.8 Ag-1 467.2 Fg-1 1 M H2SO4 2018 [159]
Carbon/Pani composite 1 Ag-1 229 Fg-1 1 M H2SO4 2018 [100]
PANI-Au nanocompo-
site
0.5 Ag-1 168.2 Fg-1 1 M H2SO4 2019 [181]
PANI-Au nanocompo-
site
10 Ag-1 135.5 Fg-1 1 M H2SO4 2019 [181]
CarbonNanofibre/PANI Ag-1 184.6 Fg-1 1 M H2SO4 2020 [182]
PANI-G Oxide Nano-
composite
1 Ag-1 264 Fg-1 1 M H2SO4 2020 [183]
Phytic acid sodium salt
doped PANI
1 Ag-1
40 Ag-1
531.5±2.177 Fg-1
355.35±2.195 Fg-1
1 M H2SO4
Present
work
Further, to check stability, the device was subjected to 1000 charging/charging
cycles at a high current density of 40 Ag-1. As illustrated in Fig. A.3.41, the PANI based
device shows an excellent stability 90 % without the loss of any appreciable amount of
specific capacitance at such a high rate of current density. To the best of our knowledge
this 90 % stability of 355.35±2.195 Fg-1 at 40 Ag-1 has never been reported on PANI,
more specifically in two electrode system which is the most practical approach to evalu-
ate the specific capacitance of the materials.
98
Figure A.3.41: Cycle stability of PANI based symmetric device over 1,000 GCD cycles
at 40 Ag−1 while inset reflects few GCD cycles at 40 Ag−1 current density.
Furthermore, Ragone plot is the most authorized way to represent the energy den-
sity and power density of the device. Based on this all energy storage system can be dif-
ferentiated and evaluated [178]. The energy density and power density were calculated by
using equations [101]. Fig. A. 3.42 display the energy density and power density of the
device at all current densities. From the plot it should be noted that there is no significant
lost in energy density as the power density is increased. The PANI symmetric superca-
pacitor showed significant enhancement in both the energy density and the power densi-
ty. It delivered an energy density of 73.82 Wh kg-1 at the power density of 500 W kg-1.
More importantly, the energy density was very stable with the increase in the power den-
sity. The energy density reached up to 49.35 Wh kg-1 even at a power density as high as
99
20000 W kg-1, which was much higher than most of current commercial supercapacitors
[101]. This is the most important characteristic of this material which has never been ob-
served in previous reports based on PANI based system [78, 100, 159,178, 181, 182, 183]
Figure A.3.42: Ragone plot for PANI based symmetric device.
It is remarkable that morphology and electrical conductivity factors plays a signif-
icant role in improving the specific capacitance and charge storage ability of the materials
[184]. Thus, our synthetic method enables concurrent tuning of both morphology and
electrical conductivity rendering strong improvement in all aspects of charge storage,
more specifically at a high current density.
100
Conclusion
Phytic acid sodium salt doped PANI samples were synthesized by an ultra-fast
and green route by oxidative polymerization technique using an environment friendly
novel dopant, phytic acid sodium salt and APS as an oxidant. The PANI salts were syn-
thesized in a very short period of time i-e 5-10 minutes with an excellent yield (98.62 %)
and higher conductivity (10 S/cm).
The synthesized phytic acid sodium salt doped PANI are processable because
they are easily soluble in a variety of polar solvents such as H2O, NMP, DMF, DMSO,
THF and ethanol. We assume incorporation of the phytic acid sodium salt into the poly-
mer chain contributed toward the best solubility and conductivity.
The elemental composition of the synthesized materials was confirmed by EDX.
The EDX spectra show all the basic elements in the polymer back bone. SEM analysis
shows nanoscale porous interconnected network a desirable morphology in charge stor-
age devices such as supercapacitors. TGA results shows that the most optimized case P-
5PA is stable up to 670 0C.
The electrochemical results show that the optimized case P-5PA render impres-
sive capacitive properties having a very low resistance. The capacitance was calculated
from CV results for a range of scan rates (20 mV to 300 mV). At low (20 mV) and high
(300 mV) scan rates the capacitance was 950 ±1.091 and 517.5 ±1.520 Fg-1 respectively.
Similarly, from GCD curves the specific capacitance was calculated for a range of current
densities (1 Ag-1to 40 Ag-1). At low (1 Ag-1) and high (40 Ag-1) current density the spe-
cific capacitance was 832.5 ±1.400 Fg-1 and 528 ± 1.357 Fg-1 respectively. The specific
capacitance results obtained from both the CV and GCD support each other.
101
Charge transfer resistance and n value for P-5PA was determined from EIS at dif-
ferent applied voltages. Parameters obtained from the proposed equivalent circuit shows
that P-5PA at 0.6 V has a small charge transfer resistance (Rct) 7.439 ohm and a high
value of n (0.769). For three electrodes system cyclic stability was performed for P-5PA
at high current density 40 Ag-1 and shows an excellent retention 95.26 % for 1000 cycles.
Furthermore, the PANI symmetric supercapacitor device was checked by GCD
for various current densities ranging from 1 to 40 Ag-1. At 1 Ag-1 the specific capacitance
was 531.5 ±2.177 Fg-1 and 355.35 ±2.195 Fg-1 at 40 Ag-1. To check stability the device
was subjected for 1000 GCD cycles at a high current density of 40 Ag-1 having excellent
retention i.e. 90%. The PANI symmetric supercapacitor showed significant enhancement
in both the energy density and the power density. It delivered an energy density of 73.82
Wh kg-1 at a power density of 500 W kg-1.
More specifically, the energy density of the device was very stable with the in-
crease in power density. The energy density reached up to 49.35 Wh kg-1 even at a power
density as high as 20000 W kg-1, which was much higher than most of currently market
available supercapacitors. These results demonstrated that the PANI salt synthesized by
this ultra-fast and green route using phytic acid sodium salt as a dopant can be effectively
used as electrode material in supercapacitors.
102
Part B
Chapter B1
Polymerization of aniline on pre-fabricated chitosan films
B.1 Introduction
Electroactive biomaterials are a part of a new generation of ‘‘smart’’ biomaterials
that allow the direct delivery of electrical, electrochemical and electromechanical stimu-
lation to cells [185, 186]. The family of electroactive biomaterials includes Intrinsically
Conductive Polymers (ICPs), electrets, piezoelectric and photovoltaic materials [186].
Electrets and piezoelectric materials allow the delivery of an electrical stimulus without
the need for an external power source, but the control over the stimulus is limited [187].
ICPs including PANI, on the other hand, can provide excellent control of the electrical
stimulus, possess very good electrical and optical properties, have a high conductivity
and can be made biocompatible, biodegradable and porous [187, 188]. Furthermore, a
great advantage of ICP is that their chemical, electrical and physical properties can be tai-
lored to the specific needs of their application by incorporating antibodies, enzymes and
other biological moieties [186, 189, 190, 191]. Additionally, these properties can be al-
tered and controlled through stimulation (e.g. electricity, light, and pH) even after synthe-
sis [192].
Tissue engineering is the emerging field of biomedical sciences is a promising
way to repair the injuries to overcome the organ shortage in clinical treatment by combin-
ing the polymeric scaffolds or patches with cells and bioactive materials [187]. These
103
conductive polymeric patches play a very significant role in the regeneration of the dam-
age tissue by providing structurally relevant environment [187, 189]. Biologically appli-
cable patches have the characteristics: 1) have porous interconnected structure, 2) have
biocompatible and biodegradable, 3) have mechanical strength for specific application, 4)
have modified surface morphology to support cell attachment and growth.
Numerous scaffolds with various ingredients have been synthesized for the regen-
eration of different tissues. ICPs have gained a great attention for applications in the field
of tissue engineering [192]. Considering the vast amount of new possibilities PANI of-
fers, we believe it will revolutionize the world of tissue engineering. Unfortunately, its
use in biological applications is limited by its low processibility, lack of flexibility and
non-biodegradability, and has been noted to cause chronic inflammation once implanted
[193, 194].
One way to compensate for the shortcomings of PANI is to use it together with
another polymer, combining the positive qualities of both materials [195]. In this regard,
different composites of PANI with polypropylene (PP), poly (ethyl 3-aminobenzoate),
gelatin, polylactide (PLA), polycaprolactone, poly (3-aminobenzoic acid) and chitosan
were created for biomedical applications [190, 196, 197].
B.1.1 Chitosan
Chitosan is a functional, linear and renewable polysaccharide biomaterial synthe-
sized from naturally occurring chitin. The chitin is a fibrous mucopolysaccharide which
is a main constituent in the exoskeletons of molluscs, insects, annelids and crustaceans
shells like crab [198]. It is the second plentiful polymer in nature after cellulose. This
natural polymer contains 2-acetamido-2-deoxy-β-d-glucose through a β (1→4) linkage as
104
shown in Fig. B.1.1. Deacetylation of chitin leads to the formation of chitosan i.e. a natu-
ral poly (amino saccharide) [199]. The chitosan contains poly (1→4)-2 amino-2-deoxy-d-
glucose unit and has been considered as an eccentric cationic polymer having significant
scientific attraction on account of its unique characteristics [199, 200].
OO
OH
OHNH2
OHO
OH
OHNH2
OO
OH
OHNH2
OH
n
Chitosan
Figure B.1.1: Chemical Structure of Chitosan.
Recently, chitosan has gained immense interest because of its wide range of ap-
plications centered on its special properties such as biodegradability, hydrophilicity, bio-
compatibility, low immunogenicity, good adsorption, non-toxicity, antibacterial proper-
ties, gel and films forming properties and has found wide applications in a variety of are-
as [199, 201, 202]. The feasible application of chitosan in a various shape such as flakes,
gels, beads and fibers, has drawn special attention in various fields. Incorporation of im-
purities like functional groups in to the chitosan matrix results in the formation of huge
numbers of chitosan derivatives. Among various chitosan derivatives, the most widely
used derivatives are mainly composed of sulphur, nitrogen and phosphorus etc [200,
203]. Further, composites of chitosan have also developed for variety of applications. Va-
riety of material have been employed for the formation of chitosan composite which in-
cludes polyurethane, activated clay, polyvinyl chloride, bentonite, poly vinyl alcohol and
ICPs such as PPy and PANI [204].
105
B.1.2 Chitosan grafted PANI Composite
As the conductivity of PANI can be controlled by protonating the imine sites in
the main chain, its applications in biomedical field recently attracted much attention
[205]. The major drawback of using PANI for biomedical applications tends to be its lim-
ited biocompatibility and biodegradability. Although it’s composite with natural biopol-
ymer usually provide a supportable medium for the biological molecules [206]. It has
been reported that the selectivity and sensitivity of PANI to biomolecules can be im-
proved through copolymerization with natural biocompatible and biodegradable polymers
having variety of functional groups such as –OH, -COOH, -NH2 and acetyl group [207].
Chitosan is a suitable candidate because of its remarkable hydrophilicity, biocom-
patibility and antibacterial properties, having hydroxyl and amino groups in their back
bone that can be easily altered. These properties in a polymer are essential for the use in
biomedical applications [208, 209]. Therefore, conductive composites have been pre-
pared by incorporating PANI into chitosan, combining the good biocompatibility and bi-
odegradability of the chitosan and the electrical conductivity of the PANI [210, 211].
Chitosan grafted PANI had found its application in various biological fields [205].
A. Tiwari and V. Singh [204] reported grafting of PANI on chitosan by oxidative radical
copolymerization using HCl as a dopant and ammonium persulphate (APS) as an oxidant.
The synthesized product had conductivity 4.03 ×10-2 with globules porous surface and
crystallinity in the grafted region. They further recommended that these conducting bio-
materials are not only cost effective and environmentally safe but also from material sci-
ence point of view are very attractive for fabrication in sensor devices.
106
S. K. Shukla et al. [210], reported that chitosan grafted PANI through oxidative
radical copolymerization at room temperature using CuSO4 as a polymerizing agent. The
grafted composite material showed improved electrical conductivity (~ 10-6 Scm-1) due to
the incorporated PANI onto chitosan. Furthermore, the composite was responsive to H+
ion, which is a suitable property of this composite for fabrication in biosensor devices.
Sajjad Sedaghat [207], carried out chemical grafting of PANI on chitosan in the
presence of H2SO4 and APS as a dopant and an oxidant respectively. He reported that the
synthesized material with relatively low conductivity with smooth and slick morphology
can find applications in polymer resistant coating, chemical sensors and storage contain-
ers.
Mihic et al. [211], grafted conjugated PPy onto chitosan backbone to produced
conductive hydrogel. They reported that the composite hydrogel significantly enhanced
heart function when injected into the hearts of rat after myocardial infection.
Panagiota Moutsatsou, et al. [206], fabricated a composite nanofibrous membrane
containing PANI and chitosan by electrospinning method at the evaluation of their bio-
compatibility. The membrane showed biocompatibility and supported cell growth and at-
tachment without any toxic effects. The hydrophilicity retention and conductivity in the
membrane was due to chitosan and PANI respectively.
Vijaya lekshmi and coworkers [212], reported that chitosan-based hybrid nano-
composites prepared by using PANI/nanosilica (PANI/SiO2) as inorganic filler and
H2SO4 as a cross-linker, possess conductivity of 8.39×10-3 Scm-1 and can be used effec-
tively as environment friendly polymer electrolyte membrane.
107
Kushwaha et al. [213], synthesized chitosan grafted PANI through in situ
polymerization and suggested the homogeneous morphology and improved stability of
grafted copolymer. They also deposited film of grafted copolymer on the ITO substrate
for urea sensing and found good sensing properties.
Cui and coworkers [214], synthesized PPy-chitosan biomaterial that has shown
high biocompatibility and conductivity. In vivo results demonstrated that PPy-chitosan
composite material can improve electrical transmission across a fibrotic scar in the in-
jured heart.
Solution casting method was reported by Pasela et al. [215], to synthesize PANI-
chitosan composites. They investigated that PANI did not affect the biocompatibility of
chitosan and can be utilized for biomedical applications.
Sangyong Lee et al. [216], prepared a Chitosan grafted PANI, to develop a sensi-
tive device which responds to the presence of hazardous acids. The synthesized chitosan
grafted PANI showed good solubility in common polar organic solvents and excellent
film forming properties.
B.1.3 Application of chitosan grafted PANI
The use of chitosan grafted PANI has gained substantial attraction due to its wide
applications in biomedical fields such as drug delivery [217], bioactuators [218], neural
and tissue engineering [219, 220].
B.1.3.1 Tissue Engineering
Tissue engineering (TE) is an important emerging topic in biomedical engineer-
ing, aim to repair the damaged or replace the lost tissue with the help of biomaterial
[221]. These biomaterials are used in the preparation of bio scaffolds. The currently em-
108
ployed scaffolds in the application of tissue engineering, show electrical resistant. Efforts
have been made to overcome this problem by incorporating conductive particles such as
nano-fibers of carbon [222] and nanowires of gold [223]. The incorporation of these con-
ductive particles in scaffolds makes the electrical transmission possible, but these incor-
porated conductive particles are not biocompatible and biodegradable. In addition, the
lack in solubility of these particles has a further drawback of inhomogeneous distribution
in the biphasic complex system. This problem in scaffolds can be managed by mixing
ICPs with biodegradable natural polymers, thus the resultant scaffolds will be biocompat-
ible and biodegradable [224].
PANI is once again a valuable option to produce electroactive and biodegradable
scaffolds. The popularity of this unique ICP can be judged in biomedical applications
from vast array of research articles published in the last few years [205-217]. Because of
biocompatibility, conductivity and processability, PANI finds its application in tissue en-
gineering. These properties make PANI and its composites attractive biomaterial compo-
nents [224, 225].
In the field of tissue engineering, bioelectronics devices have been developed by
using polymeric patches such as chitosan grafted PANI with the expectation to restore
communication among interrupted cells [226, 227]. But still under nonacidic or physio-
logical conditions, de-doping of PANI or other ICPs is a serious issue for its long-term
application in medical and biological fields [228]. Therefore, further investigation is ut-
most necessary to select appropriate dopants for ICPs that can maintain the conductive
nature of these implanted materials in both neutral and alkaline medium.
109
B.1.4 Aims and Objectives
In this section, aniline will be polymerized on a prefabricated film of chitosan us-
ing phytic acid sodium salt as a novel dopant. Taking advantage of the cationic amine
groups present on PANI and chitosan backbone and anionic (multivalent) nature of phytic
sodium salt, the chitosan grafted PANI patch is expected to maintain its conductive na-
ture by retaining the dopant. Whereas insulating nature of the chitosan is advantageous
for using as a substrate on account of its malleability, mechanically tough and detachable
conductive film formation without affecting the electrical behavior of PANI. The use of
facile fabrication method is expected to be helpful for the utilization of polymeric patches
in tissue engineering.
110
Chapter B2
B.2 Experimental
B.2.1 Materials
The detail of chemicals such as Aniline, Phytic acid sodium salt, Ammonium per-
sulphate and DI water has already been given in Part A 2 (Table A.2.1). Acetic acid was
purchased from Arcos organics USA and chitosan flakes were obtained from Sigma Al-
drich USA. All the chemicals used were analytical grade and used without further purifi-
cation.
B.2.2 Preparation of chitosan viscous solution
The Chitosan flakes (1% (w/v)) (medium molecular weight 85% deacetylation)
were dissolved in 1% (v/v) aqueous acetic acid solution. This solution was kept for con-
tinuous stirring for three hours under room temperature to obtain a viscous solution of
chitosan with pale yellow color. After this, centrifugation of the viscous solution was car-
ried out for 10 minutes at 6000 rpm for the removal of any insoluble flakes. After centrif-
ugation, this solution was stored as a stock solution for the preparation of chitosan films
on microscopic glass slides.
B.2.3 Fabrication of chitosan solution on glass slides to obtained chitosan films
Chitosan solution (0.75 ml) was uniformly spread on the surface of microscopic
glass slides (7 cm × 2 cm) and left to dry for a week at normal atmospheric pressure and
room temperature
111
B.2.4 Synthesis of chitosan grafted PANI conductive polymeric patches
For the synthesis of chitosan grafted PANI patches, the stock solutions of phytic
acid sodium salt + aniline (solutions A1-A6) and APS (solution B) for each sample, pre-
pared in Part A2 (section A.2.2) were used. All samples of chitosan grafted PANI patches
along with codes are given in Table B.2.1.
Table B.2.1: Samples name and Codes of Patches.
Samples Composition Code
0.5% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS +
1 % chitosan solution
Patch-0.5
1% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS + 1
% chitosan solution
Patch-1
3% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS + 1
% chitosan solution
Patch-3
5% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS + 1
% chitosan solution
Patch-5
7% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS + 1
% chitosan solution
Patch-7
10% phytic acid sodium salt + 0.0055 moles of aniline + 0.001 M APS +
1 % chitosan solution
Patch-10
To synthesize the chitosan grafted PANI conductive patches, 0.5 ml of phytic acid
sodium salt and aniline solutions (A1-A6) and 0.25 ml of APS solution (B) were mixed in
2 ml Eppendorf tube for each sample, shake with hand and then uniformly dispersed on
the surface of prefabricated film of chitosan (Fig. B.2.1). The dispersed solutions were
permitted to polymerize on the surface of chitosan films for an hour. After this, these
patches were rinsed extensively with DI water to wash out the unreacted phytic acid so-
112
dium salt, uncross linked polymeric chain or any type of other side products formed dur-
ing the polymerization. When the patches become well dried they were peeled out from
the surfaces of the microscopic glass slides carefully and each patch was placed in be-
tween the two glass slides for the maintenance of its flat shape.
Figure B.2.1: Synthesis of polymeric patch on glass slide. (A is the solution of phytic ac-
id sodium salt and aniline in DI water and B is the solution of APS in DI water)
B.2.5 Material Characterization
B.2.5.1 In vitro characterization physical properties of the patches
For surface morphology, all polymeric patches were analyzed by SEM (Helios G4
CX Dual Beam microscope equipped with Octane Elite) within the voltage range of 5
kV. To transform the sample for SEM a suitable amount of each sample was placed on
113
Aluminum stubs by using conductive taps. For each sample image was taken using a fo-
cused electron beam under suitable resolution and voltage. Elemental composition and
mapping, was carried out by using Helios G4 CX FEI Deutschland GmbH, Berlin Ger-
many. Conductivity was checked by Four Probe Conductometer (Jandel RM 3000)
equipped with a potentiostate. Atomic force microscopic imaging was done through 2000
nm × 2000 nm scan area via NanoWizard® 3 Bio AFM JPK/Bruker, Berlin Germany.
The roughness of the Patche was calculated from 2D Height AFM images using image
data processing software JPK Nanowizard. For functional groups conformation FT-IR
Spectrometer (Shimadzu), was used, the spectra were recorded from 400-4000 cm-1.
B.2.5.2 In vitro characterization electronic properties of the patch-5
Cyclic voltammetry measurements were recorded by using ZRA Potenti-
ostat/Galvanostat Reference 3000. The experiments were carried out by using gold coil
and Ag/AgCl as counter and reference electrode respectively. The working electrode was
FTO on which surface the patch was fabricated. The electrochemical measurements were
performed in the potential range of -0.2 to 0.8 at a scan rate of 30 mV s-1 in 1M phos-
phate buffer solution having pH 7.4 as an electrolyte. For UV measurements film with
reduced opacity, was incubated in a cuvette containing phosphate buffer solution and al-
low for the transmission of UV beam. The absorption spectra were recorded at predeter-
mined time with PerkinElmer spectrophotometer in the range between 300-1000 nm.
114
Chapter B3
B.3 Results and Discussion
B.3.1 Surface Morphology of the Patches using SEM
Morphology of the pristine chitosan and chitosan-grafted-PANI patches were in-
vestigated by high resolution SEM and are shown in Fig. (B.3.1-B.3.5). No visible pores
are observed for pristine chitosan patch (Fig. B.3.1). On polymerizing the aniline on chi-
tosan films, as the dopant (phytic acid sodium salt) concentration increases from 0.5 to 5
% (wt/v) the surface gradually become rough with uniform granular nanostructure as for
patch-3 and patch-5 (Fig. B.3.3 and Fig. B.3.4). Further increase in the dopant concentra-
tion up to 7 % (wt/v), agglomeration of the particles appears on the chitosan surface (Fig.
B.3.5 a). While further increase in the dopant concentration in the composite patch, more
agglomerated particles are clearly visible on the surface as shown in Fig. B.3.5 b.
From the SEM images of patches, the patch-3 and patch-5 presents a homogene-
ous interlinked granular morphology along with porosity. Comparative to smooth mor-
phology of the chitosan film (substrate) as shown in (Fig. B.3.1), the patch-3 and patch-5
have a rougher surface topography illustrating that the polymerization results in the uni-
form distribution of PANI on the surface of chitosan. The granular structure of PANI in
the acidic environment using chemical polymerization is an important characteristic of
PANI [115].
Comparison of patch-3 with patch-5 shows that granular particles are arranged
compactly with each other having very less porosity while in case of patch-5, uniform
granulated particles are arranged in interlinked manner having pores between the gran-
115
ules. This uniform, granulated and porous structure has great importance in biological
fields. Therefore, it can be expected that patch-5 has most promising and desirable mor-
phology amongst others.
From these results, we can say that phytic acid sodium salt as a dopant imparts
significant effect on the surface modification. Due to anionic nature of phytic acid sodi-
um salt, amine groups of chitosan can be protonated and binds to the PANI (positively
charged) resulting in the formation of blended system with strong interactions between its
components [82, 229]. The use of facile fabrication technique for the utilization of phytic
acid doped PANI-chitosan patches in terms of conductive polymeric patches is very sig-
nificant because it provides a platform to affiliate with electro responsive tissues like
heart [230].
Figure B.3.1: SEM image of chitosan.
116
Figure B.3.2: SEM image of Patch-0.5 and Patch-1.
117
Figure B.3.3: a) SEM image of Patch-3 and (a*) zoomed image of Patch-3.
118
Figure B.3.4: a) SEM image of Patch-5 and (a*) zoomed image of Patch-5.
119
Figure B.3.5: SEM image of Patch-7 and Patch-10.
120
B.3.2 Morphological studies of the Patches using Atomic Force Microscopy (AFM)
The surface morphology of the patches was further confirmed with AFM, to gain
insight into the effect of variation of the dopant concentration on chitosan grafted PANI
Patches. For each patch, 2D (Adhesion and Height) and 3D (adhesion and Height) phase
images were captured to explore the morphological characteristics of the patches after
polymerization. Fig. (B.3.6.-B.3.12) displays the AFM images of the pristine chitosan,
Patch-0.5, Patch-1, Patch-3, Patch-5, Patch-7 and Patch-10, respectively. From the AFM
images of the chitosan-grafted PANI patches, it is clear that increasing concentration of
the dopant from 0.5 % to 3 % (Wt/v) on the surface of chitosan film, granular particles
growth gradually increases as shown in Fig. (B.3.7-B.3.9). At 5 % (Wt/v) of the dopant
concentration, the Patch-5 presents a porous network composed of a homogeneously dis-
tributed interconnected granular morphology as shown in Fig. B.3.10. While further in-
crease in the dopant concentration from 7 % to 10 %, agglomeration of the particles take
place on the chitosan surface as shown in Fig. (B.3.11-B.3.12). From the extracted profile
of the 2D images, roughness for all the patches were measured (Table B.3.1). From the
roughness results it could be observed that patch-5 has rough, porous with well-defined
granular structure as shown in Fig. B.3.10, relative to the other patches. The rough and
porous topography indicating that polymerization of PANI proceeded effectively and uni-
formly on the chitosan surface [231, 232]. These results are consistent with the surface
morphology observed through SEM. This uniform interconnected granular surface of the
patch-5 is desirable in tissue engineering especially in the cardiac muscles [214].
121
Figure B.3.6: AFM image of chitosan (a and a*) 2-D and 3-D image of adhesion and (b
and b*) 2-D and 3-D image of height.
122
Figure B.3.7: AFM image of Patch-0.5 (a and a*) 2-D and 3-D image of adhesion and (b
and b*) 2-D and 3-D image of height.
123
Figure B.3.8: AFM image of Patch-1 (a and a*) 2-D and 3-D image of adhesion and (b
and b*) 2-D and 3-D image of height.
124
Figure B.3.9: AFM image of Patch-3 (a and a*) 2-D and 3-D image of adhesion and (b
and b*) 2-D and 3-D image of height.
125
Figure B.3.10: AFM image of Patch-5 (a and a*) 2-D and 3-D image of adhesion and (b
and b*) 2-D and 3-D image of height.
126
Figure B.3.11: AFM image of Patch-7 (a and a*) 2-D and 3-D image of adhesion and (b
and b*) 2-D and 3-D image of height.
127
Figure B.3.12: AFM image of Patch-10 (a and a*) 2-D and 3-D image of adhesion and
(b and b*) 2-D and 3-D image of height.
128
Table B.3.1: Roughness and Sheet resistance of chitosan grafted PANI patches calculat-
ed from 2-D image of height and four probe techniques, respectively.
Sample Code
Roughness
Sheet Resistance
(Ohm/cm2) Average Resistance
(Ra)
Root mean square
Resistance (Rq)
Pristine chitosan 13.52 nm 20.19 nm ----
Patch-0.5 18.77 nm 25.02 nm 10.6
Patch-1 26.82 nm 35.56 nm 6.4
Patch-3 40.35 nm 57.92 nm 1.8
Patch-5 51.86 nm 66.31 nm 1
Patch-7 125.1 nm 150.8 nm 28.3
Patch-10 71.10 nm 94.56 nm 43.2
B.3.3 Sheet Resistance of the Patches
The sheet resistance of the synthesized patches i.e. Patch-0.5, Patch-1, Patch-3,
Patch-5, Patch-7 and Patch-10 according to the dopant concentration by increasing from
0.5 to 10 % (Wt/v) while keeping the concentration of aniline and oxidant constant, was
measured by four-probe method (Table B.3.1). The most optimized patch i.e. Patch-5
having low sheet resistance across the surface. This low sheet resistance of the Patch-5
corresponds to the uniform nanoscale interconnected granular network like structure
which is clear from SEM and AFM analysis. This uniform interconnected granular struc-
ture of Patch-5 reduces the inter-chain separation between the PANI polymeric back-
bones [214]. Patch-5 presents the optimal electrical property, roughness, porosity and in-
terconnected granular morphology thus can be a potential candidate for tissue engineer-
ing especially in electrochemical responsive tissues such as cardiac muscles because the
above-mentioned properties are reported to be beneficial for repairing such type of tissues
[101, 233].
129
B.3.4 Energy-Dispersive X-Ray Spectroscopy and Elemental Mapping
To investigate the elements and chemical composition of pristine chitosan and
chitosan-grafted PANI patches, EDX analysis and surface mapping of elements of patch-
es are employed and presented in Fig. B.3.13-B.3.19. The results of EDX spectra demon-
strated that the composition of pristine chitosan consists of C, N and O with detected
atomic ratios of 52.89 %, 21.53 % and 25.58 as shown in Fig. B.3.13. While chitosan
grafted PANI patches are mainly composed of C, N, O, Na and P. The detection of O, P
and very small percentage of Na peaks in all the patches revealed the successful incorpo-
ration of phytic acid sodium salt in to the polymer backbone as phytic acid salt molecule
is responsible for the introduction of corresponding peaks in the PANI structure.
The experimental results illustrated that increase in content of dopant results in
the enhancement of percentage of the Phosphorus (P) and sodium (Na). High percentage
of P and Na is assumed to be responsible for low sheet resistance. The detected atomic
ratios of P and Na were respectively 1.72 % and 0.68 % for Patch-0.5 (Fig. B.6.14), 1.89
% and 0.45 % for Patch-1(Fig. B.3.15), 2.04 % and 0.50 % for Patch-3 (Fig. B.3.16),
2.28 % and 0.72 % for Patch-5 (Fig. B.3.17), 1.67 % and 0.62 % for Patch-7 (Fig.
B.3.18) and 1.57 % and 0.53 % for Patch-10 (Fig. B.3.19). Among these, Patch-5 depicts
high percentage of P and Na which leads to the uniform and cross-linked globular net-
work like structure [84]. The EDX elemental maps suggest the uniform distribution of P
and Na along with other elements.
130
Figure B.3.13: EDX and Elemental mapping of pristine chitosan.
131
Figure B.3.14: EDX and Elemental mapping of Patch-0.5.
132
Figure B.3.15: EDX and Elemental mapping of Patch-1.
133
Figure B.3.16: EDX and Elemental mapping of Patch-3.
134
Figure B.3.17: EDX and Elemental mapping of Patch-5.
135
Figure B.3.18: EDX and Elemental mapping of Patch-7.
136
Figure B.3.19: EDX and Elemental mapping of Patch-10.
137
B.3.5 FTIR Spectroscopy
Fig. B.3.20 shows the comparison of FTIR spectra of chitosan and polymeric
patch-5. The chitosan film spectrum shows expected absorption peak at 3435 cm-1 (-NH2
stretching) and the bands 1782-1436 cm-1 (-NH2 bending). The band located at 2976 cm-1
is assigned to the C-H stretching mode in the chitosan [234]. The peak at 1261 cm-1 indi-
cate (anti-symmetric stretching of C-O-C bridge), while the peak at 1142 cm-1 correspond
to the (skeletal vibration of the C-O stretching), and these are characteristics of its sac-
charide structure [235]. The patch-5 infrared spectrum manifests all the characteristics
peaks corresponding to chitosan and PANI. The band observed at 3214 cm−1 depicts -
NH2 stretching with 20 amino groups in chitosan [236]. The bands observed at 1559 cm−1
depicts the stretching mode of C=O, it is generally due to saccharide [237]. The appear-
ance of C=C stretching mode of quinoid ring and benzenoid ring at 1400 cm−1 and 1291
cm−1, respectively are characteristics of PAni [84]. The bands at 1178 cm−1 are attributed
to the C-N stretching. The detection of bands at 903 cm−1 depicts the anti-symmetrical C-
O and is generally due to the saccharide structure [238]. The appearances of the bands in
the range of 797 cm-1 are allocated to vibration of P-O bond [73, 239]. The band around
700 cm−1 is associated with P-O-C stretching vibration [240]. The bands at 570 cm−1 rep-
resent the C-OH (out-of-plane) deformation [234]. Therefore, the detection of respective
bands in the spectrum of patch-5 should be attributed to the incorporation of phytic acid
sodium salt into PANI backbone indicate the successful polymerization of aniline on the
chitosan film.
138
Figure B.3.20: FTIR spectra of chitosan and Patch-5.
B.3.6 Cyclic voltammetry (CV)
Fig. B.3.21 a, b, demonstrate CVs of the patch-5 before and after incubation in
phosphate buffer solution. From the Fig. B.3.21 a, it can be noted that the obtained cyclic
voltammogram have characteristic emeraldine salt features of PANI, indicated by two re-
dox couples, a primary couple at 0.37 V (anodic) and 0. 54 V (reduction) and a secondary
couple at -0.18 and 0.47 V. Although the CV measurement was carried out in phosphate
buffer with a pH 7.4, but still these characteristics are identical to a typical PANI in a pH
less than 6.0, this is due to the internal acidic environment produced by the phytic acid
sodium salt molecules. Further we recorded the CVs after 3, 6, 9, 12, 15, 18 and 21 days
139
incubation in the phosphate buffer and displayed in Fig. B.3.21 b. From the CVs curves it
can be noticed that gradually a slight increase in peaks separation occurred indicating that
charge transfer becoming difficult with the passage of time. From the Figure it can be
seen that even at 21 days the only primary redox couple appeared similarly as expected
for more alkaline pH always [241]. Although the patch remained conductive over the en-
tire incubation period in a neutral pH, unlike those PANI films doped with other conven-
tional acids that shows negligible electrochemical properties at a pH always less than 4,
because the dopant is lost [6, 242]. The electrochemical activity observed from the CVs
curves for the polymeric Patch-5 in phosphate buffer solution illustrate that incorporation
of the dopant phytic acid sodium salt during the polymerization of aniline on chitosan
film is a feasible methodology to produced conductive materials that show electrocatalyt-
ic activity under a physiological relevant environment for extended period of time. While
the patch included a substantial amount of the insulator chitosan film as a substrate, after
polymerization of aniline, it shows that effective amount of charge transport occurs
through the polymeric patch even in the phosphate buffer as an electrolyte.
140
Figure B.3.21: a) Cyclic Voltammogram of Patch-5, b) CV curves of Patch-5 recorded at
0 day, 3rd day, 6th day, 9th day, 12th day, 15th day, 18th day and 21th day in phosphate buff-
er.
B.3.7 UV-Vis spectroscopy
Electronic structure of PAni (Fig. B.3.22 a) could be examined by observing the
characteristic absorbance peaks at, 351 nm due to p-p* transition of the benzenoid group,
427 nm due to polaronic shoulder, and 826 nm due to the polaron region. The peak at
427 nm corresponds to the electrically conductive state of PANI, the emeraldine salt
[241]. Beside this, another broad peak can also be noticed in the region between 793 and
826 nm, which is also another typical peak for the conductive emeraldine salt form of
141
PANI [243]. To understand the effect of the incubation time on the electronic structure of
the synthesized polymeric patch, sample of the patch-5 was incubated in phosphate buffer
solution and their UV-Vis spectra were recorded at different time intervals as shown in
Fig. B.3.22 b. To evaluate the effect of incubation time on the protonated form of the
polymeric patch, we concentrated on the peak in the range of 422-427 nm. From the Fig-
ure it can be observed as the incubation time increased a decreased in the wavelength
along with absorption of the peak from 427 to 422 nm was observed, suggesting that the
level of doping decreased with the incubation time of the patch in the phosphate buffer
solution. This decreased in the peak was attended by a blue shift in the region of polaron
centered at 793 nm indicating the decrease in conductive state of the patch. The shifting
of the polaronic peak from 826 to 793 nm suggests that the fabricated patch is still in
conductive form even after 21 days of incubation period. These changes observed in the
spectral peaks agree with the changes in CVs curves (Fig. B.3.21 b). Thus the results ob-
tained from the UV demonstrate that the patch maintained protonated species for 3 weeks
in phosphate buffer solution, because of the peak presence in the region of 427 to 422 nm
in all measured spectra.
These results indicate that our methodology of polymerizing the aniline in the
presence of phytic acid sodium salt as a dopant leads to a conductive polymeric patch of
chitosan grapted PANI that shows conductivity for extended period of time (21 days) in
physiological conditions.
142
Figure B.3.22: (a) UV-Visible spectrum of Patch-5 and (b) UV-visible spectra of Patch-
5 recorded at 0 day, 5th day, 10th day, 15th day and 21th day.
143
Conclusion
Polymerization of aniline was carried out using phytic acid sodium salt as a do-
pant and APS as an oxidant on chitosan film prefabricated on glass slides to obtain con-
ductive patches. According to the concentration of the dopant, six (6) polymeric patches
i.e. Patch-0.5, Patch-1, Patch-3, Patch-5, Patch-7 and Patch-10 were synthesized. Strong
chelation between the dopant salt and chitosan was observed in the case of Patch-3 and
Patch-5 and lead to conductive polymeric patches that will retain electroactivity and low
surface resistivity, respectively.
Elemental analysis shows that the polymerization was carried out successfully be-
cause all basic elements are present in the polymeric patches. Functional groups detection
was done by FTIR. SEM analysis show porous interconnected granular morphology for
Patch-3 and Patch-5. The Patch-5 has more uniform porous interconnected nanoscale
granular structure as compared to Patch-3. The surface topography was further confirmed
by AFM.
The AFM results shows that Patch-5 is more porous and rough as compared to the
other patches and the results are consistent to the results obtained from SEM. Sheet re-
sistance of these patches was measured by Four-probe, and the results shows that Patch-5
possess the lowest resistance as compared to the other patches. This uniform intercon-
nected nanoscale granular surface of the patch-5 is desirable in tissue engineering espe-
cially in the cardiac muscles.
The electrochemical stability of patch-5 was checked by recording the CVs after
3, 6, 9, 12, 15, 18 and 21 days incubation in the phosphate buffer having pH 7.4. The ob-
tained results illustrated that incorporation of the dopant phytic acid sodium salt during
144
the polymerization of aniline on chitosan film is a feasible methodology to produced
conductive materials that show electrocatalytic activity under a physiological relevant
environment for extended period of time. Further, the effect of the incubation time on the
electronic structure of Patch-5 showed the retention of protonated species for 3 weeks in
phosphate buffer solution.
Future perspectives
For electrochemical applications, the most important approach is to synthesis new
materials, which must satisfy the conditions of 1), good conductivity 2), high surface area
with more active sites 3), electrochemical stability for good cycling performance 4), and
have high rate ions diffusion.
Owing these properties, the as synthesized materials will be fabricated for other
various energy storage devices for commercial applications. Furthermore, as the electro-
chemical capacitors (ECs) electrode material investigation directions are nanoscale com-
posite materials, therefore nanocomposite of these materials will be prepared with metal
oxide for constructing a novel hybrid electrode for ECs.
Another effective point will be to chase new electrolyte with good electrochemi-
cal activity and reversibility, to contribute additional pseudo capacitance in specific po-
tential window. The problem of electrochemical stability for the composite electrode sys-
tem should to be given more attention in further.
Furthermore, vitro and vivo study of the fabricated conductive polymeric patches
will be carried out in future.
The development of our nanostructured PANI with enhanced processability and
exceptional functionality may offer great promise in fields such as sensors, electrochrom-
145
ics, photovoltaics, corrosion protection etc. The rapid development in the synthesis, mor-
phology control and novel properties of nanostructured PANI will continue to spur fur-
ther commercial interest in this promising material.
146
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