Study On The Electrocatalytic Behavior And Conductivity Of Ir-Sn Oxide Electrode

The oxide coating electrode is one of the most important electrochemical electrode materials. The oxide coatings should have high electroconductivity and good catalytic performance, which are essential for superior electrodes. Therefore, it is necessary to systematically study the electrocatalysis and conductive mechanism of the electrodes, which will help us to better optimize the performance of electrodes.Electrode materials containing IrO2 have been widely used in anti-erosion fields. In this paper, the IrxSn1-xO2 electrodes prepared by thermal decomposition were studied. The effects of component on the electrochemical properties were characterized by open-circuit potential, cyclic voltammetry and polarization curves. The characteristic impedance was studied by ac impedance spectroscopy to explore its electrocatalysis performance. The microstructures and morphologies were analyzed by XRD、DTA and TEM methods. The electronic structure of the iridium-tin composite oxide with optimum performance was calculated by first-principles calculation method.It’s shown that open-circuit potential of the electrodes was mainly controlled by Ir(Ⅲ/Ⅳ) transformation on the electrode surface. When the molar content of IrO2 was 30%, the charge reached the maximum value of 116.5mC·cm-2 in acidic solution and 111mC·cm-2 in basic solution respectively. In the low potential range, Tafel slopes of the electrodes were between 55-61mV and the order reaction of H+ was-1. The oxygen reaction mechanism should be controlled by the step S-OH*ads�'S-OHads. The equivalent circuit Rn(RfCf)(RctCd1) was used to fit the impedance spectra. Impedance spectroscopy of Ir0.3Sn0.7O2 electrode had greatly affected by electrode potentials. Its impedance spectra measured at 0.3V showed an ideal polarized state. Concentration polarization and electrochemical polarization occured at the same time measured at 0.75V. When measured at 0.85V, it showed typical impedance characteristics for OER. The electrode process was affected by more factors such as the resistance of solution, the charge transfer resistance of a faradaic process, double-layer capacitance, solution concentration and diffusion. Ir0.3Sn0.7O2 had the biggest double-layer capacitance with a value of 81.63mF·cm-2(E=0.3V) compared with other electrodes. And its charge transfer resistance were only 2.5Ω(E=0.85V) and 1.2Ω(E=0.875V). For all electrodes, their charge transfer resistances decreased exponentially as potential increased between 0.8V and 0.9V. While the potential was higher than 0.9V, charge transfer resistances diminished slowly. The coating structure of Ir0.3Sn0.7O2 electrode changed from non-crystalline to nanocrystalline with the heat temperature increasing. When the oxide coating was heated at 450℃, the grain size was about 10nm. The band gap of SnO2 was 1.1eV. After doping Ir atom to the SnO2 lattice, both conduction-band width and valence-band width of Sn0.75Ir0.25O2 were significantly widened. The electron transporting of SnO2 mainly relied on O2p state and Sn 5s state. Because Fermi energy entered the conduction band, the conduction mechanism had changed greatly by doping with Ir. So Ir 5d electronic state played an important role in its conductivity. Compared with SnO2, the electronic effective mass of Sn0.75Ir0.25O2 was reduced and the carrier concentration increased about 1000 times. Adding small amount of Ir can effectively increase the properties of SnO2-based coatings.