New degradation mechanism of Ti/IrO2 + MnO2 anode for oxygen evolution in 0.5 M H2SO4 solution

Degradation mechanism of Ti/IrO2(0.7) + MnO2(0.3) anode for oxygen evolution was studied in 0.5 M H2SO4 solution by field emission scanning electron microscopes (FESEM), Tafel slope, X-ray diffraction (XRD) and electrochemical impedance spectroscopic (EIS). The whole surface of the non-electrolyzed Ti/IrO2(0.7) + MnO2(0.3) anode consisted of nano-IrO2 poles array. The anode surface had hardly discovered cracks and had compact morphology that can prevent the electrolyte from entering the Ti/oxide interface and an insulating TiO2 film from growing on the Ti-based surface. An insulating TiO2 phase had not been generated on the Ti/oxide interface during the process of O2 evolution and the inactive anode surface still remained mass of the IrO2 and MnO2 oxides. The chemical dissolution of Ti/IrO2(0.7) + MnO2(0.3) anode coating was not the main reason for electrode degradation in 0.5 M H2SO4 solution. The degradation mechanism of Ti/IrO2(0.7) + MnO2(0.3) anode differed from other conventional oxide electrodes for O2 evolution in acid medium. The platforms of Tafel slope and anode potential (900–1050 h) indicated that the change of the oxygen evolution reaction (OER) mechanism was the main reason for degradation of Ti/IrO2(0.7) + MnO2(0.3) anode due to the change of adsorption intermediate.