Unexpected increasing Co valence state of an exsolved catalyst by Mo doping for enhanced oxygen evolution reaction

Developing and understanding efficient catalysts for anodic oxygen evolution reaction (OER) is critical for the electrochemical production of H2 for energy storage and transformation. Herein, a Co0.76Fe0.18Mo0.06O1.35 catalyst with a spinel structure (CFMO-800) was prepared from Mo-doped LaCo0.8Fe0.2O3 perovskites (LCF) by a simple exsolution method. The CFMO-800 catalyst exhibited a low potential of 1.48 V (vs. RHE) at a current density of 10 mA cm−2 in 1 M KOH surpassing all spinel and perovskite Co/Fe oxide catalysts reported. The surface-sensitive soft X-ray absorption spectroscopies (SXAS) at the Co-L2,3 and the O-K edges revealed an unexpected increase in the Co valence state of CFMO-800 upon doped with the high-valence Mo and the clear formation of Co/Fe (oxyhydr)oxides on the surface layers of the exsolved catalyst. This study presents a strategy for the surface reconstruction by combining the exsolution and the high-valence ion doping to develop highly active electrochemical catalysts.