Ruthenium‐Based Mixed Oxides as Electrocatalysts for Oxygen Evolution in Acid Electrolytes

Ruthenium oxide, prepared by the thermal decomposition method, has the highest known initial electrocatalytic activity for oxygen evolution in acid electrolyte. However, this material is not stable in the electrolyte and at the same time exhibits a significant increase of oxygen overpotential with time, probably due to a chemical transformation of the oxide from a lower to a higher valence state. Efforts were made to stabilize ruthenium by preparing mixed oxides with Ir and/or Ta using the thermal decomposition method. The electrocatalytic activities for oxygen evolution on these oxides in 1 N H 2 SO 4 were determined using the potentiostatic method. The surface areas of these oxides were estimated using cyclic voltammetry. Dual Tafel slopes (approximately 30 and 40 mV) were found on most of these oxides. The ternary oxide ( RuIr 0.5 Ta 0.5 O x ) exhibited a single Tafel slope of 30 mV, had the lowest overpotential, and showed minimum variation of overpotential with time.