An oxygen evolution Co–Ac catalyst – the synergistic effect of phosphate ions

Abstract

Formation of an amorphous cobalt based oxygen evolution catalyst called Co–Pi has been recently reported from a neutral phosphate buffer solution containing Co²⁺. But the concentration of Co²⁺ is as low as 0.5 mM due to poor solubility of a cobalt salt in phosphate medium. In the present study, a cobalt acetate based oxygen evolution catalyst (Co–Ac) is prepared from a neutral acetate buffer solution, where the solubility of Co²⁺ is very high (>100 times in comparison with phosphate buffer solution). The Co–Ac possesses better catalytic activity than the Co–Pi with an additional advantage of easy bulk scale preparation. The comparative studies on the oxygen evolution reaction (OER) activity of Co–Ac and Co–Pi in phosphate and acetate buffer electrolytes reveal that the Co–Ac exhibits enhanced synergistic catalytic activity in phosphate solution, probably due to partial substitution of acetate in the catalyst layer by phosphate, resulting in the formation of a Co–Ac–Pi catalyst.