Degradation characteristics of IrO2-type DSA in methanol aqueous solutions

In this paper, a comparative study has been done on the long-term stability and deactivation characteristics of IrO₂-type DSA^® in acidic solutions with the absence and the presence of methanol compound, respectively. The long-term stability is evaluated by accelerated lifetime tests. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements are carried out on the electrodes before and after deactivation, by which the failure characteristics of Ti-supported oxide electrodes are deduced. The service life is found to increase and then decrease with increasing the calcination temperature of the as-prepared electrodes; on the other hand, the lifetime is obviously shortened by the addition of methanol into the testing solution. The latter phenomenon can be interpreted by more severe dissolution of titanium base and active oxide layers in methanol-involved solution than in blank one. But the former one (temperature-dependent lifetime) cannot be simply explained by the progressive enhancement of stability of active IrO₂ layer with the heating temperature, as concluded from the continuous decrease in change rates of crystalline orientation, unit cell volume and microstrains of oxide layers with the temperature, after the deactivation. SEM observation shows a coating peeling off within the oxide layer and the total delamination of oxide coating at the metal/oxide interface of samples prepared at high temperature after the failure, due to the low coating adhesion. The ease of mechanical loss of oxide layer is considered as one of the main reasons for rapid deactivation of Ti/IrO₂ electrodes prepared at high temperature, although the oxide layer itself in these electrodes is chemically stable enough.