Electrochemically deposited graphene oxide thin film supercapacitors: Comparing liquid and solid electrolytes

In the present work, graphene oxide (GO) thin films were prepared on ITO substrates by electrochemical deposition for different voltages and deposition times and were further electrochemically reduced by cyclic voltammetry (CV). Reduced GO films (rGO) were used in the manufacturing of supercapacitors with solid-state electrolyte based on a freeze-thawed PVA-Na2SO4 hydrogel. GO and rGO films were tested using SEM, XRD, RAMAN and XPS techniques for comparative reasons. The specific capacitance of the electrodes and supercapacitors were estimated by electrochemical methods. XRD analysis revealed increase of the rGO interlayer spacing after multiple CV cycles that was assigned to incorporation of the electrolytic agents such as sodium ions of the electrolyte. Raman spectra showed that the I-D/I-G ratio associated with the graphene matrix defects remained fairly constant even after several CV cycles, meaning that no new defects were added. It was the XPS analysis that confirmed the reduction of GO to rGO as well as the presence of sodium in the rGO films. The optimum value of the electrode capacitance of the constructed model supercapacitor with thin rGO films and PVA-20%Na2SO4 electrolyte was 8.55 mF/cm(2) that approaches the electrode capacitance value of 10.67 mF/cm(2) measured with liquid Na2SO4 electrolyte.