The Roles of Composition and Mesostructure of Cobalt‐Based Spinel Catalysts in Oxygen Evolution Reactions

By using the crystalline precursor decomposition approach and direct co‐precipitation the composition and mesostructure of cobalt‐based spinels can be controlled. A systematic substitution of cobalt with redox‐active iron and redox‐inactive magnesium and aluminum in a cobalt spinel with anisotropic particle morphology with a preferred 111 surface termination is presented, resulting in a substitution series including Co(3)O(4), MgCo(2)O(4), Co(2)FeO(4), Co(2)AlO(4) and CoFe(2)O(4). The role of redox pairs in the spinels is investigated in chemical water oxidation by using ceric ammonium nitrate (CAN test), electrochemical oxygen evolution reaction (OER) and H(2)O(2) decomposition. Studying the effect of dominant surface termination, isotropic Co(3)O(4) and CoFe(2)O(4) catalysts with more or less spherical particles are compared to their anisotropic analogues. For CAN‐test and OER, Co(3+) plays the major role for high activity. In H(2)O(2) decomposition, Co(2+) reveals itself to be of major importance. Redox active cations in the structure enhance the catalytic activity in all reactions. A benefit of a predominant 111 surface termination depends on the cobalt oxidation state in the as‐prepared catalysts and the investigated reaction.