A simple and large-scale synthesis technique was developed to fabricate a nano-wedge IrO 2 /MnO 2 hybrid film electrode for highperformance electrochemical supercapacitors. When the galvanostatic charge/discharge rate was increased from 2.96 to 296 A g −1 , the specific capacitance of the electrode declined from 573.5 to 379.2 F g −1 with a relatively limited loss of 34%. In particular, the hybrid film electrode presents a loss of only 4.9% in the specific capacitance after 1000 cycles.Supercapacitors (also called electrochemical supercapacitors or ultracapacitors) have attracted increasing attention as energy storage devices due to their high power density, fast charge-discharge rate, and excellent cycling stability. 1-3 Carbonaceous materials, conductive polymers, transition-metal oxides, and hybrid composites have been used to fabricate supercapacitor electrodes. Among these candidates for electrode materials, MnO 2 has been considered to be one of the most attractive due to its low cost, natural abundance, environmental friendliness, and high theoretical capacitance of ∼1370 F g −1 . 4,5 However, the poor electrical conductivity of MnO 2 (10 −5 -10 −6 S cm −1 ) restricts the rate capability for high power performance, 6-8 and the charge/discharge process of MnO 2 is only involved in a very thin surface layer of the MnO 2 electrodes, resulting in a low utilization of MnO 2 and limitations of the pseudocapacitive properties. 9 To improve the electrical conductivity and to maximize the utilization of MnO 2 , the hybrid composite nanostructure with a low fraction of MnO 2 on the highly conductive substrate was proposed due to the reliability of its electrical connection, which has become one of the main criteria in designing high-performance electrodes for MnO 2 -based supercapacitors. Recently, various nanoscale films of MnO 2 were loaded on to the highly conductive materials, such as graphene, 10 ZnO nanorods, 11 and conducting polymer. 12 In this paper, we demonstrate the design and fabrication of a novel hybrid nano-architecture by anodically electrodepositing MnO 2 film on the highly electrically conductive IrO 2 nano-wedges that grow on the pretreated Ti plate to achieve high specific capacitance, energy and power density, as well as long-term life for supercapacitor electrode applications. ExperimentalNano-wedge IrO 2 on the surface of a Ti substrate was prepared by thermal decomposition of H 2 IrCl 6 hydrosolvent, as described in our previous work. 13 The final calcination was extended to 2 h for the formation of nano-wedge IrO 2 film at 400 • C in air. MnO 2 films were deposited on the pretreated substrate or on the IrO 2 film by applying a current density of 500 μA cm −2 in a mixed solution of 0.5 M MnSO 4 + 0.5 M H 2 SO 4 at 20 • C. After electrodeposition, the MnO 2 film and IrO 2 /MnO 2 hybrid film electrodes were taken out and washed carefully with deionized water to remove excessive electrolyte, then placed on a sheet of clean paper in a vacuum oven at 120 • C for 2 h.The phases of the IrO 2 , MnO ...
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