Study on the Effect of G/CNT on the Enhanced Capacitance of IrO2-ZnO-G(CNT)/Ti Electrodes

Abstract Compounding different materials to be the electrode is a good way in the field of supercapacitors. IrO2 was used as an active and conductor oxide, and ZnO was used as a semiconductor oxide. Carbon nanotube (CNT) and Graphene (G) were used to prepare the electrodes of IrO2-ZnO-carbon nanotube (CNT)/Ti and IrO2-ZnO-graphene oxide (G)/Ti by thermal decomposition method and their different effect on the properties was studied in detail. The surface of IrO2-ZnO-CNT/Ti had a "hill-bag" structure, and the IrO2-ZnO-G/Ti had a graphene sheet layered fold structure, their specific surface area and pore volume were significantly greater than that of an electrode without carbon material. The specific capacitances of IrO2-ZnO-G/Ti and IrO2-ZnO-CNT/Ti were 681 F g-1 and 501F g-1, respectively, which were higher than IrO2-ZnO/Ti (399 F g-1). The capacitance retention rate of the IrO2-ZnO-G/Ti electrode coating was 80.24% after 20,000 cyclic tests, which was worse than that of IrO2-ZnO/Ti (90.65%). The addition of carbon materials reduced the cycle stability, but the binding effect of graphene and the coating was better than that of carbon nanotubes. Graphene improved the overall performance better than that of carbon nanotubes. A binder-free asymmetric supercapacitor working in H2SO4 solution was assembled with RuO2-MoO3/Ti and IrO2-ZnO-G/Ti as cathodic and anodic electrode respectively. It exhibited the energy densities of 29.6 W h kg-1 and 25.3 W h kg-1 when the power density was 700 W kg-1 and 3505 W kg-1 respectively. The preliminary charge/discharge mechanism of the asymmetric supercapacitor in the H2SO4 solution was presented.