2011 IEEE First Conference on Clean Energy and Technology CET

SPEEKIPES Composite Membranes as an Alternative for Proton Exchange Membrane in

Microbial Fuel Cell (MFC)

Wan Ramli Wan Dauda,b*, Mostafa Ghasemia,b, Chong Poh Shea,b, Jamaliah Md. Jahima,b, Lim Swee Sua and Mana} IsmaW,b

aFuel Cell Institute, Universiti Kebangsaan Malaysia bDepartment of Chemical and Process Engineering, Engineering Faculty , Universiti Kenagsaan Malaysia

43600 UKM, Bangi, Malaysia Email: wramli@eng.ukm.my Tel: +6 0389216050, Fax: +6 0389216024

Abstract-A solid polymer electrolyte (SPE) membranes were synthesized by incorporation of sulfonated poly(ether ether

ketone) (SPEEK) in poly(ether sulfone) (PES) for electricity

generation in microbial fuel cells (MFC). The composite

membranes were prepared at 5% percent weight of SPEEK

mixed with PES by phase inversion method and characterized by

measuring proton conductivity, oxygen diffusion, water crossover

and level of biofouling. Membrane electrode assemblies (MEA) were made by hot pressing the composite membranes with a Pt­

loaded cathode on one side of membranes. The MEA, with

effective area of 9 cm2, were tested using single chamber MFC.

The blended SPEEKIPES membrane had low resistivity to water

crossover and oxygen diffusion while high in conductivity compared to Nation and PES membranes. The MFC using the

composite membranes generated an average power density of 140

mW m-2 which was double that produced by MFC using Nation

membranes in every fed-batch cycle which lasted for 24 hours.

The experimental results suggested that SPEEKIPES composite

membrane could be a promising alternative to costly

perfluorosulfonate membranes as proton exchange membrane in

MFC system.

Keywords-SPEEK, PES, composite membrane, microbial fuel cell, electricity generation

I. INTRODUCTION

In the past decade the power density of microbial fuel cells (MFCs) have increased nearly six orders of magnitude. The majority of this improvement was achieved by replacing MFC's materials and modifying reactor architecture which are cheaper and more effective [1]. An early two-chamber design using Nafion proton exchange membrane (PEM) as a separator between the anodic and the cathodic chambers had a maximum power of 0. 53 mW m·2 and overall chemical oxygen demand (COD) removal efficiency of 92.6% when rice mill wastewater was used as the electron donor. The performance of the MFC was improved by replacing the PEM separator with earthern pot which yielded a maximum power density of 2. 3 mW m·2

by increasing the overall COD removal to 96. 5% [2].

Integration of a two-stage wastewater treatment process with a biocathode without a membrane separator to form a membrane-less MFC, combined with other modification in the

978-1-4577-1354-51111$26.00 2011 © IEEE 400

system architecture, raised the power density up to 70 m W m·2

and the overall COD removal efficiency of 99%, primarily because of the higher proton flow without the membrane [3 ].

While modem designs have reduced the cost of materials used in MFCs especially that of PEM, there is no work has been conducted using separators made from polyethersulfone (PES)/sulfonated poly(ether ether ketone) (SPEEK) composite membranes which are cheaper than other PEM. SPEEK was previously blended with other polymers and used in direct methanol fuel cells (DMFCs) [4-8] to decrease methanol permeability and in PEM fuel cell (PEMFC) [9-11] to decrease the permeability of hydrogen through the membrane.

In this paper, the effect of PES/SPEEK composite membrane on MFC's performance was investigated because little is known about major electrochemical losses of this composite membrane in MFC system. The proton conductivity of the membrane were expected to affect the power output by contributing to the overall internal impedance of the MFC system. Electrochemical impedance spectroscopy was utilized to investigate the losses caused by the membrane and to delineate the individual contribution from different resistance to the overall cell impedance [12-14]. The water losses and oxygen diffusion through this membrane were also expected to affect microbial growth and performance of the MFCs. It is vital to characterize the membrane in order to better understand the effect of this membrane in the MFC.

II. MATERIAL AND METHODS

A. Production ofSPEEKfor membrane fabrication

For preparation of SPEEK, 20 gram of PEEK (Goodfellow Cambridge Limited, UK) was dissolved slowly in 500mL of 95-98% concentrated sulphuric acid (R & M Chemicals, Essex, UK) and stirred vigorously until all of PEEK dissolved completely. The SPEEK solution was then poured into a large excess of ice water and SPEEK precipitated. The solid was gathered by Whatman filter paper Grade 1 and washed several times by distilled water until the pH of remaining retentate was nearly 7. PES and SPEEKIPES membranes were fabricated by phase inversion method. Briefly, the required amount of PES

2011 IEEE First Conference on Clean Energy and Technology CET

and SPEEKIPES at 70°C were dissolved in I-methyl-2-pyrrolidone (NMP) (Merck, Germany) and then dispersed uniformly by mechanical stirrer. The solution was then left to stand for at least 24 hours to release dissolved bubbles. The solution was then cast on glass plate by a casting knife and left in a solution (mostly water) to separate the membrane from glass plate.

B. Water losses and oxygen diffusion

Water losses in MFCs were mainly caused by water diffusion across membrane to the air. To measure the losses of water from MFC, the mass of MFC were measured using an analytical balance for the next 3 days. Each sample was taken every 24 hours. The percentage of water losses was calculated using the equation below:

Total water loss at time t (%) = Initial weight of contain (g)-Final weight of contain after time t (g)

x 100% Initial weight of contain (g) ( 1 )

A dual chamber MFC without electrodes and membrane holder in the centre was use to measure the diffusion of oxygen crossover. Each chamber was constructed with a total volume of 110 mL and 9 cm2 opening in the centre to allow oxygen diffusion through the membrane. Phosphate buffer solution (PBS) with 50 mM concentration was used as media in both chambers. An aquarium pump was used to disperse oxygen from the air in the PBS until it was saturated with oxygen. The other chamber was purged with nitrogen gas to eliminate oxygen and a dissolved oxygen (DO) probe was located in the centre of the chamber. An YSI 5100 DO meter (YSI Incorporated, Ohio, USA) was used to measure the DO value from the DO probe at every 15 min. The mass transfer coefficient of oxygen in the membrane, ko was determined using the equation by Kim et al. [15]:

kO=-:tIn[CO�CI] (2)

where V is the liquid volume in the anode chamber, A is the membrane cross-sectional area, Co is the saturated oxygen concentration in the cathode chamber and c is the DO in the anode chamber at time t. The diffusion coefficient Do was calculated as Do = kat, where L is the membrane thickness.

C. Electrochemical impedance spectroscopy

Before and during operation in MFC, the membranes were subjected to electrochemical impedance spectroscopy (EIS) measurements to obtain their conductivity properties. A frequency response analyzer (FRA) (Model 1255 Solartron Analytical, UK) equipped with an electrochemical interface was connected to a PC to control the measurement frequency ranges. Measurement frequency was ranged from 0 - 10 kHz to obtain a Z" - Z' graph using ZPlot®IZViewTM software. The half circle curve plotted in Z" - Z' graph was analyzed using existing "Fit Circle" function in the software to calculate the resistance of the membranes.

D. MFCs operation and data capture

The anode was made from plain carbon paper (P75T, AvCarb©) and the cathode was made from the same carbon

978-1-4577-1354-5/11/$26.00 2011 © IEEE 401

paper that was coated with 0.3 mg/cm2 Pt catalyst. The membrane was then placed on the coated side of the cathode and was hot pressed together at 110 °C and 13.8 MPa for 3 min. Nafion membranes were treated with deionized water, 3% H202, deionized water, 1M H2S04 and deionized water at 80°C for 1 hour at each step. The membranes were stored separately in deionized water prior to use. The cathode-membrane assembly was sealed in the anodic chamber by sandwiching with two silicone gaskets. The cathode was exposed to oxygen present in the air while the membrane was placed directly beside the cathode to secure the medium from leaking out of the chamber. The anode (2.5cm x 6.0 cm) was placed inside the middle of the closed chamber. The anode and the cathode were constructed from plain carbon paper and a piece of titanium plate was connected to the carbon paper before been sealed. A piece of copper wire approximately 10.0 cm in length was pierced through the titanium plate to provide connection point to the external load and circuitry. An external resistance of 1000 (1 was connected from the anode to the cathode to acclimatize the MFCs.

MFC output was start recorded after 2 months of operation in volts (V) against time by using a Fluke 8846A multimeter and connected to a PC through USB-RS232 cable. The recorded data were collected and analysed using the data logging software FlukeView® Forms Basic version 3.3 (Fluke Corporation, Washington, USA).

III. RESULTS AND DISCUSSION

A. Water Losses

Water losses in PES-based membranes were slightly higher than in commercial Nafion 117 membrane as shows in Fig 1. Total water loss in MFC with Nafion 117 was as low as 0.79% compared to 0.95 and 1.15% in MFCs using the PES/SPEEK 5% membrane. The high water losses from PES/SPEEK membranes was caused by aggregation of the hydrophilic phase into ionic clusters [16]. The interactions between sulfonic acid groups in SPEEK chains increased the hydrophilic sulfonic groups aggregating into larger ionic clusters which led to a random distribution of ion channels with good connectivity.

Figure 1

B. Oxygen diffusion

In the MFC, it is important to block the oxygen from migrating across the membrane and entering the anodic chamber. Power generated from the MFC drops because the oxygen are being used as electron acceptors by the bacteria rather than by the anode because the former is more thermodynamically favorable. The rate of oxygen diffusion through the membranes was shown in Fig. 2. PES membrane had the lowest permeability for oxygen followed by Nafion 117 and SPEEK 5% membrane. However, Nafion and PES membrane was slightly different compared to SPEEK 5%. Both

2011 IEEE First Conference on Clean Energy and Technology CET

membranes effectively blocked the permeability of oxygen after 4 hours with a DO of 1.2 and 1.5 mg L -1. The permeability rate for SPEEK 5% membrane was high at 5.0 mg L-1 DO after 4 hours test. Table I shows the oxygen diffusion properties of the various membranes. Diffusion coefficient for SPEEK 5% was the highest with 19.44 x 10-6

cm2 S-l followed by those of Nafion 117 (3.14 x 10-6 cm2

S-l) and PES (0.75 x 10-6 cm2

S-l) .

Figure 2

Table 1

C. Conductivity

The conductivity of the Nafion membrane was the highest compared to those of SPEEK 5% and PES membranes before they were tested in the MFC. However, the conductivity of PES-based membranes were higher than Nafion because of the former hydrophilic properties during MFC operation. The percentage of increase before and during MFC operation was shown in Fig. 3. Membrane electrical resistance (MER) of the Nafion membrane increased during MFC operation from 15.65 to 19.1 n cm2 because of biofouling effect [17]. The PES­based membrane contains hydrophilic sulfonate functional group that could effectively integrate with water to lower the value of MER [16].

Figure 3

D. Voltage and Power Generation

The trend of voltage change over time was similar to the trend of power density change over time. From Fig. 4(a) and (b), the MFC with SPEEK 5% produced 450 mV of voltage which is equivalent to 140 mW m-2 of power density in every cycle with fresh medium. The power output was two-fold higher than MFC using Nafion membrane (70 mW m-2). The PES membrane produced very little power. SPEEK was an important materials to blend in the PES membrane in order to increase the MER and conductivity of the membrane caused by the presence of sulfonate functional groups [16, 18].

IV. CONCLUSION

The SPEEKIPES composite membrane showed low resistivity to water crossover and oxygen diffusion while high in conductivity compared to Nafion and PES membranes. However, the membranes could generate an average power density of 140 mW m-2 which was 2-fold higher than Nafion membrane at every new cycle. The SPEEKIPES composite membrane is a good alternative to replace the costly pertluorosulfonate (Nafion) membrane in MFC.

978-1-4577-1354-5/11/$26.00 2011 © IEEE 402

A. Figures and Tables

TABLE I. SPECIFICATION OF THE MEMBRANES TESTED fN THIS STUDY

Type of membrane Thickness (mm) k. (10-4 cm/s) Do (10-6 cm'/s) N-117 0.18 1.74 3.14 PES 0.05 1.49 0.75 PES/SPEEK 5% 0.15 12.96 19.44

1.4 �

� 1.2 on on £ 1.0

� 0) � 0.8

<0 0.6 � � 0.4 0) � 0.2 �

0.0

CTotalloss at Day 3 DTotalloss at Day 2 IITotalloss at Day 1

N-117 PES

Type of Membrane

PES/SPEEK 5%

Figure I. Water losses through different type of membranes in MFC

6 3 Ob 5 -5 t: 4 0) oD ;>.. o 3 ""

2 0) >

� is

0

0

_ N-117 _PES _ PES/SPEEK 5%

50 100 150 Time (min)

200 250 300

Figure 2. The change of dissolved oxygen concentration in anodic chamber by using different type of membranes

I.OE-04

E I.OE-05 u � I.OE-06 o :� I.OE-07 u .g I.OE-08 t: o

u I.OE-09

1.0E- 10

N- 1 17 PES PES/SPEEK 5%

Type of Membrane

200 ""

150 � (1)

100 S uo

50 g ..., o :;-(') -50 �

(1) -IOO� - 150

�

Figure 3. Conductivity of the membrane before and during operated in MFC with percentage of conductivity differential was calculated

2011 IEEE First Conference on Clean Energy and Technology CET

600

500 :> 5 400 ., 00 S 300 "0 > 0) 200

u 100

o

180

;::;-160 E 140 ;:: 120 E -; 100

.� 80 ., o 60 � 40 o

0. 20 o

o

o

----SPEEK5% -

2 3

Time (day)

(a)

----SPEEK5% - • PES

2 3 Time (day)

(b)

- N·117

4 5

4 5

Figure 4. Cell voltage (a) and power density (b) during operation of MFC using different type of membrane (arrow indicated fedding at the

end of each batch cycle

ACKNOWLEDGMENT

The authors would like to thank Universiti Kebangsaan Malaysia for supporting this work through UKM Research University Grant No.: UKM-GUP-BTT-07-30-187 and UKM Arus Perdana Project Grant No.: UKM-AP-TK-05-2009, and the Malaysian Toray Science Foundation for supporting this work through the Young Scientist Research Grant No.: MTSF 09/G48.

REFERENCES

[I] Z. Du, H. Li and T. Gu, "A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy," Biotechnol Adv, 25(5), pp. 464-482, Sep-Oct, 2007 [2] M. Behera, P. S. Jana, T. T. More and M. M. Ghangrekar, "Rice mill wastewater treatment in microbial fuel cells fabricated using proton exchange membrane and earthen pot at different pH," Bioelectrochemistry, 79(2), pp. 228-233, Oct, 2010 [3] A. Aldrovandi, E. Marsili, L. Stante, P. Paganin, S. Tabacchioni and A. Giordano, "Sustainable power production in a membrane-less and mediator­less synthetic wastewater microbial fuel cell," Bioresour Technol, 100(13), pp. 3252-3260, Jul, 2009 [4] H. Cai, K. Shao, S. Zhong, C. Zhao, G. Zhang, X. Li and H. Na, "Properties of composite membranes based on sulfonated poly(ether ether ketone)s (SPEEK)/phenoxy resin (PHR) for direct methanol fuel cells usages," Journal of Membrane Science, 297(1-2), pp. 162-173, 2007 [5] R. Gosalawit, S. Chirachanchai, S. Shishatskiy and S. P. Nunes, "Sulfonated montmorillonite/sulfonated poly(ether ether ketone)

(SMMT/SPEEK) nanocomposite membrane for direct methanol fuel cells (DMFCs)," Journal of Membrane Science, 323(2), pp. 337-346, 2008

978-1-4577-1354-5111/$26.00 2011 © IEEE 403

[6] X. Li, C. Liu, D. Xu, C. Zhao, Z. Wang, G. Zhang, H. Na and W. Xing, "Preparation and properties of sulfonated poly(ether ether ketone)s

(SPEEK)/polypyrrole composite membranes for direct methanol fuel cells," Journal of Power Sources, 162(1), pp. 1-8,2006 [7] H. Maab and S. P. Nunes, "Modified SPEEK membranes for direct ethanol fuel cell," Journal of Power Sources, 195(13), pp. 4036-4042, 2010 [8] J.-C. Tsai and C.-K. Lin, "Acid-base blend membranes based on Nafion®/aminated SPEEK for reducing methanol permeability," Journal of the Taiwan Institute of Chemical Engineers, 42(2), pp. 281-285, 20 I I [9] S. Kaliaguine, S. D . Mikhailenko, K . P . Wang, P . Xing, G . Robertson and M. Guiver, "Properties of SPEEK based PEMs for fuel cell application," Catalysis Today, 82(1-4), pp. 213-222,2003 [10] H. Li, G. Zhang, W. Ma, C. Zhao, Y. Zhang, M. Han, J. Zhu, Z. Liu, J. Wu and H. Na, "Composite membranes based on a novel benzimidazole grafted PEEK and SPEEK for fuel cells," International Journal of Hydrogen Energy, 35(20), pp. 11172-11179,2010 [I I] S. Sambandam and V. Ramani, "SPEEK/functionalized silica composite membranes for polymer electrolyte fuel cells," Journal of Power Sources, 170(2), pp. 259-267, 2007 [12] Z. He and F. Mansfeld, "Exploring the use of electrochemical impedance spectroscopy (EIS) in microbial fuel cell studies," Energy & Environmental Science, 2(2), pp. 215-219, 2009 [13] A. K. Manohar, O. Bretschger, K. H. Nealson and F. Mansfeld, "The use of electrochemical impedance spectroscopy (EIS) in the evaluation of the electrochemical properties of a microbial fuel cell," Bioelectrochemistry, 72(2), pp. 149-154, Apr, 2008 [14] R. P. Ramasamy, Z. Ren, M. M. Mench and J. M. Regan, "Impact of initial biofilm growth on the anode impedance of microbial fuel cells," Biotechnol Bioeng, 101(1), pp. 101-108, Sep 1,2008 [15] J. R. Kim, S. Cheng, S. E. Oh and B. E. Logan, "Power generation using different cation, anion, and ultrafiltration membranes in microbial fuel cells," Environ Sci Technol, 41(3), pp. 1004-1009, Feb 1,2007 [16] Y-S. Ye, Y-C. Yen, c.-c. Cheng, W.-Y Chen, L.-T. Tsai and F.-C. Chang, "Sulfonated poly(ether ether ketone) membranes crosslinked with sulfonic acid containing benzoxazine monomer as proton exchange membranes," Polymer, 50(14), pp. 3196-3203, 2009 [17] M. J. Choi, K. J. Chae, F. F. Ajayi, K. Y. Kim, H. W. Yu, C. W. Kim and I. S. Kim, "Effects of biofouling on ion transport through cation exchange membranes and microbial fuel cell performance," Bioresour Technol, 102(1), pp. 298-303, Jan, 2011 [18] S. Zhong, X. Cui, H. Cai, T. Fu, K. Shao and H. Na, "Crosslinked SPEEK/AMPS blend membranes with high proton conductivity and low methanol diffusion coefficient for DMFC applications," Journal of Power Sources, 168(1), pp. 154-161, 2007