Degradation mechanism of long service life Ti/IrO2-Ta2O5 oxide anodes in sulphuric acid

Ageing performances of long service life Ti/70%IrO2-30%Ta2O5 (at mole fraction) anodes prepared at 450 degreesC over the whole electrolysis time in H2SO4 solution have been investigated. It is showed that. the Whole electrolysis processes of these anodes can be divided into three stages consisting of 'active', 'stable' and 'de-active' regions. In the first two stages, the dissolution of coated oxides is dominated (with IrO2 component preferential loss) which results in decreasing of apparent Current for oxygen evolution and voltammetric charge. It is found that, in these two stages, the preferential orientations of (1 1 0 ) and (1 0 1) planes in IrO2 rutile decreases with electrolysis time. and that of (0 0 2) plane increases, while the preferential orientations remain to be stabilized in the 'de-active' region. Therefore, the loss mechanism of catalyst coatings in this region is changed. Electrochemical impedance spectroscopy measurernent shows a slight increase in reaction resistance (R-ct) of oxide catalysts for oxygen evolution in the 'de-active' region, while a sharp rise in totally physical impedance of the whole anode. According to the experimental results, a degradation mechanism of the Ti based anodes has been proposed by degradation of Ti/catalyst layer interface resulting from the dissolution and anodic oxidation of metal base alternatively. (C) 2002 Published by Elsevier Science Ltd.