Supplementary Information
For
A 1 V supercapacitor device with nanostructured graphene oxide/polyaniline composite materials
Deepak Kumar, Anjan Banerjee, Satish Patil and Ashok K Shukla
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
Methods for synthesis of graphene oxide (GO) and reduced graphene oxide (rGO)
Graphene oxide was synthesized by a improved method [ACS Nano, 4 (2010) 4806–4814]. In brief, a 9:1 mixture of concentrated H2SO4/H3PO4 (360:40 ml) was added under vigorous stirring below 10°C to a mixture of graphite flakes (1.0 g, 1 wt equiv.) and KMnO4 (6.0 g, 6 wt equiv.), producing a slight exothermic reaction that raises the reaction temperature to about 40°C. The reaction vessel was then heated to 50°C under mechanical stirring for 12 h. The reaction vessel was cooled to room temperature and contents were slowly poured onto ice (~200 ml) containing 30% H2O2 (2 ml). The above solution was centrifuged (4000 rpm for 1 h), and the supernatant matter was decanted away. Remaining solid material was then washed in succession with 200 ml of water, 200 ml of 30% HCl, and 200 ml of ethanol (4 times); for each wash, the mixture was agitated in the solvent followed by centrifuging (4000 rpm for 1 h) and the supernatant was decanted. A solid product thus obtained was vacuum-dried overnight at 50°C.
Graphene oxide was reduced by hydrazine hydrate as reported elsewhere [Carbon 45 (2007) 1558–1565]. In brief, 500-ml round-bottom flask containing 300 ml water with 300 mg GO was uniformly dispersed. This dispersion was sonicated for 2 h until it became clear with no visible particulate matter. Hydrazine hydrate (3 ml) was subsequently added to the suspension and the solution heated with stirring bar in an oil bath at 100°C under a water-cooled condenser for 15 h. Reduced GO gradually precipitated out as a black solid. The product was isolated by filtration over a medium fritted glass funnel, washed copiously with water (3 × 100 ml) and methanol (3 × 100 ml), and dried under vacuum.
Supplementary Figures
Figure S1. FT-IR spectra for GO and rGO. Characteristic peaks for GO appear owing to the O–H stretching vibration (3369 cm−1), carbonyl C=O (1720 cm−1), aromatic C=C (1618 cm−1), carboxy C–O (1379 cm−1), epoxy C–O (1151 cm−1) and alkoxy C–O (1042 cm−1). Characteristic peaks for rGO appear due to O–H stretching vibration (3429 cm−1), C–H stretching (2919 cm−1), aromatic C=C (1671 cm−1) and alkoxy C–O (1018 cm−1).
Figure S2. Raman spectra for GO and rGO. Characteristic D and G bands for GO and rGO appear at 1342, 1569 cm−1 and 1345, 1570 cm−1, respectively.
Figure S3. Amperometric profiles for PANI and GO/PANI composite.
Figure S4. FT-IR spectra for PANI and GO/PANI composite film in KBr pellet. For PANI, peaks at 1588 and 1466 cm−1 correspond to the characteristic C=C stretching mode of the quinoid and benzenoid rings, respectively. Peaks at 1124 and 803 cm−1 are assigned to in-plane and out-of-plane bending of the C–H. Peaks at 1301 and 1239 cm−1 are attributed to C–N and C=N stretching mode. GO/PANI composite film mainly shows the characteristic peaks of the polymer matrix. It is noteworthy that peaks corresponding to quinoid and benzenoid rings, respectively, of the PANI matrix in the composite film shift to higher wavenumbers (1638, 1481 cm−1). Interactions including π–π stacking, electrostatic interactions and hydrogen bonding existing between GO and PANI [ACS Appl. Mater. Interfaces 2 (2010) 821–828] are believed to cause the spectral changes.
Figure S5. Optimization of sulphuric acid electrolyte concentration. Specific-capacitance values are obtained from cyclic voltammograms at 1 mV s−1 scan rate and –0.2 to 0.8 V potential window vs. Ag/AgCl reference.
Figure S6. Nyquist plot for activated carbon-based supercapacitor electrode, fabricated without rGO additive (active material composition: 95% activated carbon and 5% PVDF binder).
Figure S7. Comparative cyclic voltammograms for activated carbon (AC)-based supercapacitor electrodes, fabricated in the presence and absence of rGO additive.