Enhanced pseudocapacitance and electrolyte-wettability of graphene

hydrogels to tailor high mass loading all-solid-state supercapacitor

with ultra-high volumetric energy densityZhongqian Song a,b,Weiyan Lia, Yu Baoc*, Zhonghui Sunc, Lifang Gaoa,b, Mian

Hasnain Nawaza, Dongxue Han ac and Li Niua,c*c

aState Key Laboratory of Electroanalytical Chemistry, c/o Engineering Laboratory for

Modern Analytical Techniques, CAS Center for Excellence in Nanoscience,

Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,

Changchun 130022, Jilin, China

bUniversity of Chinese Academy of Sciences, Beijing, 100039, China

cCenter for Advanced Analytical Science, c/o School of Chemistry and Chemical

Engineering, Guangzhou University, Guangzhou 510006, P.R. China

E-mail:lniu @ ciac.ac.cn , ybao@gzhu.edu.cn

Fig. S1 TGA curves of GH and PAGH indicating the influence of PA on the GH

thermal properties

Fig. S2 Schematic illustration of PAGH formation mechanism.

As shown in Fig. S2, graphene oxide possesses lots of oxygenated groups on edges

and basal plane, such as epoxy, hydroxyl and carboxyl groups. During the

hydrothermal process, due to the introduction and dissociation of PA, the epoxy

groups can react with H+ via ring opening reactions and are converted to hydroxyl

groups. Meanwhile, the hydrogen bonding between PA and graphene oxide and the

formation of phosphate ester could prevent the oxygen groups from being eliminated,

forming the special phenol structures on the PAGH.

Fig. S3 (a)Nitrogen adsorption-desorption isotherm and (b) pore size distribution of GH and PAGH, indicating the enhanced specific surface area and optimized microstructures of PAGH.

Fig. S4 CV curves of (a) GH and (b-f) PAGH at 10 mV s -1, indicating the enhanced intensity of redox peaks with increasing PA content.

Fig. S5 (a) The PA content in PAGH, demonstrating that the PA content increases with the initial PA volume. (b-h) The energy dispersive X-Ray spectra (EDX) of original GH and PAGH. The weight ratio of PA in PAGH is calculated by using the weight contents of phosphorus clement in EDX.

Fig. S6 The conductivities of GH and PAGH, indicating decreased trends due to the

structural defects on graphene sheets.

Fig. S7 Determination of the infinite sweep rate capacitance of PAGH200 electrode.

The overlay capacitance Q is a combination of bulk charge storage (Qbulk) and

capacitive process (Qcapacitive). By plotting the capacitance with v-1/2to obtain a straight

line, the y-intercept (v = ∞) is the infinite-sweep rate capacitance. Since the

polarization effect at high sweep rates could result in deviation from a straight line,

the intermediate sweep rates were selected to extrapolate to they-intercept.

Fig. S8 CV curves of GH and PAGH150 in 1 M NaCl solution at 50 mV s -1. The larger integral area of CV curve of PAGH150 than that of GH indicates enhanced capacitance for PAGH electrode due to the enhanced electrolyte accessible area.

Fig. S9 CV curves of PAGH solid-state supercapacitor device with different mass loading. Good rectangular shape could be obtained even at a high mass loading of 10.5 mg cm-2.

Fig. S10 (a) CV curves and (b) GCD curves of PAGH solid-state supercapacitor device with a mass loading of 3 mg cm-2.

Fig. S11 CV curves of HSSC device at different bending angle. Scan rate is 200 mV s-

1

It is found that the CV curves of the HSSC device under various bending angles almost overlap, indicating high flexibility and negligible capacitance decay under various deformations.

Table S1 Comparison of the volumetric capacitance, power and energy densities of reported supercapacitors.

Materials Electrolyte Rate CV (F cm-3) PV (mW cm-3)

EV (mW h cm-3)

Ref.

PAGH 1 M H2SO4 20 A g-1 38.9 - -

This work

PVA/ H2SO4 1 mA cm-2 57.43 25 7.982500 5.63

rGO/GO/rGO GO/ H2SO4 - - 890 1.24 [1]

GH 1 M H2SO4 1 A g-1 31 - - [2]

3D porous RGO-5

1 M H2SO4 1 A g-1 55.2 7800 1.11 [3]

rGO/Fe3O4 3 M KOH 1 mV s−1 178.3 6210 5.6 [4]

rGO/Fe3O4 PVA/KOH 6.4 mA cm-3 0.25 3 0.035 [5]

Janus Graphene film

PVA/ H2SO4 0.2 mA cm-2 20 40.3 2.78 [6]

rGO/niquel nanocone3D substrate

PVA/Na2SO4 0.05 mA cm-2 1.72 4 0.15 [7]

Free-standing GO films

EMIM BF4/MeCN

25 mA cm-3 ~0.6 800 1.36 [8]

CNT/PPy PVA/H2SO4 50 mA cm-3 4.9 150 0.26 [9]

MVNNs/CNT PVA/H3PO4 25 mA cm-3 7.9 400 0.54 [10]

PEDOT paper PVA/LiCl 0.5 A cm-3 144 52 1 [11]

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