Origin of Anomalous Activities during Oxygen Evolution Reaction in Cubic CoNiCuFe Prussian Blue Analogue

Amorphous oxide catalysts typically exhibit excellent activity toward oxygen evolution reaction (OER) due to a large number of undercoordinated sites or lattice defects, but also generally suffering from low stability and difficulty in characterizing the structure. Herein, we report a well-crystallized cubic CoNiCuFe prussian blue analogue (PBA) catalyst with anomalous activities in electrocatalyzing OER when compared with its amorphized oxide. In situ Raman spectroscopy revealed a much more abundant MOOH active phase accumulated on the cubic CoNiCuFe-PBA surface than that on the amorphous CoNiCuFe-oxide surface. Further characterizations demonstrate that more high-valence metal (i.e. Co3+, Ni3+) sites are available on the cubic CoNiCuFe-PBA surface at the initial state, which is suggested to be more susceptible to redox-active surface hydroxylation and serve as the origin of active sites during OER process. The maintained cubic framework structure as well as the lower valence of Fe could contribute to considerably better stability. Such findings would open up a new door to future highly active and stable catalyst designs.