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

This is the authors' abstract. We don't add key points for this paper.

Compounding different materials with different properties to be one electrode is a good and common way in supercapacitors. IrO 2 was used as an active and conductive oxide, and ZnO was used as a semiconductive oxide to change the band gap of IrO 2 . Carbon nanotubes (CNT) and graphene (G) were used to improve the microstructure of the oxides. The electrodes of IrO 2 -ZnO-carbon nanotube (CNT)/Ti and IrO 2 -ZnO-graphene oxide (G)/Ti were prepared by a thermal decomposition method, and the different effects of CNT or G on the properties were studied in detail. The surface of IrO 2 -ZnO-CNT/Ti had a “hill-bag” structure, and the IrO 2 -ZnO-G/Ti had a graphene sheet-layered fold structure. Their specific surface area and pore volume were significantly greater than those of an electrode without a carbon material. The specific capacitances of IrO 2 -ZnO-G/Ti and IrO 2 -ZnO-CNT/Ti were 681 and 501 F g –1, respectively, which were higher than that of IrO 2 -ZnO/Ti (399 F g –1 ). The capacitance retention rate of the IrO 2 -ZnO-G/Ti electrode coating was better than that of IrO 2 -ZnO/Ti within 15,000 cycles but less than that of IrO 2 -ZnO/Ti after 15,000 cycles. Moreover, only a retention rate of 80.24% after 20,000 cycles was kept, which was worse than that of IrO 2 -ZnO/Ti (90.65%). The reasons were worth further investigation. 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 carbon nanotubes. A binder-free asymmetric supercapacitor working in H 2 SO 4 solution was assembled with RuO 2 -MoO 3 /Ti and IrO 2 -ZnO-G/Ti as cathodic and anodic electrodes, respectively. It exhibited energy densities of 29.6 and 25.3 W h kg –1 when the power densities were 700 and 3505 W kg –1, respectively. The primary charge/discharge mechanism of the asymmetric supercapacitor in the H 2 SO 4 solution was presented.