Nano-Wedge IrO2/MnO2 Hybrid Film Electrode for Electrochemical Supercapacitors

Abstract

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 ...

Micropore-Dominant Vanadium and Iron Co-Doped MnO2Hybrid Film Electrodes for High-Performance Supercapacitors

“…As shown in Figure 7a, all the semicircles of the undoped MnO 2 film electrode and the V+Fe co-doped MnO 2 hybrid film electrodes in the high frequency of Nyquist pattern are extremely small compared to the related literature reports, 56,57 which should be attributed to the interlayer of highly electrically conductive IrO 2 nano-wedges. 39 The phase angles of the doped MnO 2 hybrid film electrodes are ∼80 • (close to the value of 90 • for ideal capacitors) at the wide frequency range of 0.01-2 Hz, which is higher than that of the undoped MnO 2 film electrode (See Figure 7b). Therefore, the above results indicate that the co-doped MnO 2 hybrid film electrodes possess a greatly enhanced charge storage capability compared with the undoped MnO 2 film electrode.…”

“…Our previous work indicates that the specific capacitance of the IrO 2 interlayer on the Ti substrate is nearly negligible in comparison with those of the undoped and doped MnO 2 hybrid films. 39 Figures 6a, 6b and 6c show that the V+Fe co-doped MnO 2 hybrid film electrodes have higher specific capacitance and areal capacitance than that of the undoped MnO 2 film electrode at the same charging-discharging rate, which should be attributed to the higher specific surface area due to the presence of the dominant micropores in the doped MnO 2 hybrid films. In particular, the specific capacitance of the V+Fe co-doped MnO 2 hybrid film electrodes prepared at a current density of 25 mA cm −2 is calculated to be 426 F g −1 (245 mF cm −2 ) at the GV chargingdischarging rate of 0.2 A g −1 .…”

“…Electrode preparation.-The highly conductive IrO 2 nanowedges on the pre-treated titanium plate (Ti/IrO 2 ) were prepared by the thermolysis of a H 2 IrCl 6 aqueous solution, as reported in our previous work. 39,40 The V+Fe doped MnO 2 hybrid film on the Ti/IrO 2 nano-wedges were anodically co-electrodeposited by using different current densities (5,25,50 ). To offset any additional factors, all of the undoped MnO 2 film and the V+Fe co-doped MnO 2 hybrid films on the Ti/IrO 2 nano-wedges were necessary to ensure roughly the loading amount of 2.2-2.4 mg on an area of 4 cm −2 .…”

“…Using the highly conductive IrO 2 nano-wedges as the electrode substrate can ensure a large contact area and a reliable interface, which decrease the interface resistance and increase the cycling life of the MnO 2 hybrid film electrode. 39 The microstructure of the doped MnO 2 hybrid film electrode was regulated and controlled by the current density of the electrodeposition. The microstructure and pseudocapacitive performance for the doped MnO 2 hybrid film electrode was systematically investigated.…”

Co3O4 nanowires@MnO2 nanolayer or nanoflakes core–shell arrays for high-performance supercapacitors: The influence of morphology on performance

“…Whereas, the low electric conductivity [11] and slow diffusion of ions [12] in metal oxides including MnO 2 severely hamper the electrochemical performance of pseudocapacitors from reaching the satisfactory level. To address this problem, the effective way is to build up a delicate MnO 2 nanostructure which ensures both of massive specific surface area (SSA) and smooth electrolyte ions diffusion tunnels [13,14]. Core-shell architecture is one of the advanced nanostructures that could significantly improve the performance of supercapacitors [15,16].…”