Highly active postspinel-structured catalysts for oxygen evolution reaction.

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, Ca B 2 O 4 ( B = Cr 3+ , Mn 3+ , and Fe 3+ ), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides La B O 3 and spinel oxides Zn B 2 O 4 . Electrochemical impedance spectroscopy reveals that the higher OER activities for Ca B 2 O 4 series are attributed to the lower charge-transfer resistances. A density-functional-theory calculation proposes a novel mechanism associated with lattice oxygen pairing with adsorbed oxygen, demonstrating the lowest theoretical OER overpotential than other mechanisms examined in this study. This finding proposes a structure-driven design of electrocatalysts associated with a novel OER mechanism.