Investigation of the electrical properties, charging process, and passivation of RuO2–Ta2O5 oxide films

Freshly prepared RuO2–Ta2O5 thin films containing between 10 and 80 atom% Ru have been examined and characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and morphological analysis (SEM – scanning electron microscopy/EDS – energy dispersive X-ray spectroscopy). Investigation of the electrical properties, charging process, and passivation of the electrode containing RuO2–Ta2O5 thin films was conducted as a function of electrode composition in a 0.5 mol dm−3 H2SO4 solution. For potential values in the double layer region (0.2–1.0 V vs. RHE), the impedance profile observed at low frequency domain was attributed mainly to the capacitive behavior of the oxide/solution interface. As for the high frequency domain, the impedance profile gave evidence that the kinetic process is limited by supporting electrolyte/water diffusion inside the pores of the difficult-to-access oxide regions and/or the Ti/oxide interface. The electrode passivation mechanism toward OER (oxygen evolution reaction – 1.5 V vs. RHE) was also investigated during long-term electrolysis (j = 750 mA cm−2 and T = 80 °C) by means of EIS at pre-established times. The SEM–EDS data give evidence of the increase in the TiOx interlayer. Moreover, the EIS data furnished complementary insight that helped our proposition of the deactivation mechanism.