Research On The Capacitance Performance Of Anodes Coated With Ir-Ce Based Oxides

Electrode material is one of the most important factors in determining the properties of the supercapacitors. Iridium oxide, IrO2, which stored energy by redox reaction of iridium ions, has a very high theoretical pseudocapacitance. Moreover, IrO2 also has metallic conductivity and excellent resistance to acid and alkali corrosion, so it is considered to be the excellent capacitor electrode material. So far there is only a few literatures were published on the IrO2 electrodes for supercapacitors. The capacitive performance of RuO2 electrodes can be effectively increased by adding moderate Ce content.But the effect of adding Ce to IrO2 on the capactive performance has been less researched. In present, IrO2-CeO2 and IrO2-SnO2-CeO2 coatings were prepared by thermal decomposition method as the electrode for supercapacitors. The phase structure and morphology of the electrodes were characterized by XRD and SEM. The electrochemical properties were systematically studied by cyclic voltammetry, constant current charge and discharge and electrochemical impedance spectroscopy. The results were as follows:(1) Preparation temperature has a significant influence on the structure and capacitive performance performance of Ti/Ir0.7Ce0.3O2 electrode. With the preparation temperature increasing, the structure of Ir0.7Ce0.3O2 coatings transition from amorphous to crystalline structure. The degree of crystallization increases gradually. Specific capacitance increases first with increasing temperature and then decrease. When it’s prepared at 38O℃, the capacitance reaches the maximum. Capacitance of the electrode prepared at 380℃ increases about 6.8% after 8000 charge-discharge cycles. It indicates that the electrode has excellent charge-discharge cycling stability.(2) Composition makes a markedly impact on both the microstructure and cpacitive properties of the Ti/IrO2-CeO2 electrodes. The crystallization decreases with increasing in CeO2 content, indicating CeO2 inhibit the crystallization of IrO2. The Ti/IrO2-CeO2 electrode reaches its maximum capacitance capability at the 60 mol% CeO2 content, whereas possesses poor power characteristics. The electrode with 40 mol% CeO2 has relatively high capability combining with good power characteristics. The resistance of the electrode decreases with the CeO2 content, and as the CeO2 content up to 80 mol%, the electrode just a resistor.(3) The capacitive performance of the Ti/Ir0.3Sn0.7O2 electrode can be effectively improved as part of SnO2 was replaced by CeO2. The crystallization of IrO2-SnO2-CeO2 decreases with increase of CeO2 content, and a completely amorphous microstructure was obtained as CeO2 content excess 30 mol%. The specific capacitance of 392.3 F/g and 505.7F/g were observed for 10mol% and 20 mol% CeO2 content respectively; this value are higher than that of the Ti/Ir0.3Sn0.7O2 electrode. Above 20 mol% CeO2 content, the power characteristics will be damaged with increasing CeO2 content, it probably attributed to the electrode conductivity declining.(4) Electrochemical impedance spectroscopy (EIS) was employed to investigated the specific capacitance of the Ti/Ir0.3Sn0.5Ce0.2O2 electrode prepared at 340℃, and 380℃. The specific capacitance of 522 F/g,490 F/g were observed for the two electrodes, respectively, which much higher than that calculated from cyclic voltammetry. The higher value of specific capacitance can be attributed to low ohmic drop can be obtained by EIS. In addition, the inner and outer active surface areas of the Ti/Ir0.3Sn0.5Ce0.2O2 electrodes were also calculated by fitting the impedance data. It maybe provide a new analysis method to deal with the inner and outer active surface areas.