The durability of the thermally decomposed IrO2-Ta2O5 coated titanium anode in a sulfate solution

Abstract

In this work, series of IrO2-Ta2O5 anodes were investigated. The catalytic activity towards oxygen evolution reaction (OER) of these anodes are determined by calcination temperature, coating loading (coating thickness), pretreatment of titanium substrate and coating method. The difference in OER performance among the anodes are ascribed to the crystallinity of the IrO2 phase and the phase composition of the coatings. The durability of the anodes were also studied by conducting an accelerated lifetime test (ALT) in acidic 0.9 mol L−1 Na2SO4 solution at a current density of 5 kA m−2. An anode prepared at a moderate temperature exhibits an excellent lifetime of almost one year although its catalytic activity is not the best. Nevertheless, using the electrostatic spraying method to replace the hand-brush method in the coating preparation can prolong the service life even further and with less amount of coating loading. Moreover, it reveals that the coating loss or combined with titanium substrate passivation results in the eventual deactivation of the anodes during ALT. No critical value of the amount of the residual iridium was found in this work to predict the eventual deactivation before forming the passive oxide film. In addition, the deactivation of the anodes strongly depends on the calcination temperature.