The OER is confined to oxide-like surfaces, which often re-structure under operando conditions. Experimental development of oxygen evolving catalysts is done separately for acidic water electrolysis and alkaline media electrolysis . State of the art OER catalysts for acidic electrolysis are based on noble metal oxides such as RuO 2 and IrO 2 , the scarcity of which adversely affects large scale deployment of this technology. Alkaline electrolyzers employ more abundant (and affordable) catalysts based on oxides of transition metals such as Ni .