Photocatalytically reduced graphite oxide electrode for electrochemical capacitors

Graphene sheets are an ideal carbon material with the highest area available for electrolyte interaction and can be obtained by reducing graphite oxide (GO). This study presents the photocatalytic reduction of GO in water with mercury-lamp irradiation. The specific capacitance of the reduced GO in an H₂SO₄ aqueous solution reached levels as high as 220 F g^-1. This is because of the double layer formation and the reversible pseudocapacitive processes caused by oxygen functionalities at the sheet periphery. The rate capability for charge storage increases with irradiation time due to the continued reduction of oxygenated sites on the graphene basal plane. Alternating current impedance analysis shows that prolonged light irradiation promotes electronic percolation in the electrode, significantly reducing the capacitive relaxation time. With a potential widow of 1 V, the resulting symmetric cells can deliver an energy level of 5 Wh kg^-1 at a high power of 1000 W kg^-1. These cells show superior stability, with 92% retention of specific capacitance after 20 000 cycles of galvanostatic charge-discharge.