Understanding Structure-Dependent Catalytic Performance of Nickel Selenides for Electrochemical Water Oxidation

In this study, we systematically explore the connection between electrical conductivity and catalytic activity of OER catalysts and disclose the association between the structure of non-oxide-based catalysts and the corresponding OER activity, using a category of Ni-based materials as a model system: i.e., the serial Ni-based compounds NiO, NiSe, Ni3Se2, a and Ni with a wide range of continuously adjustable band gaps ranging from insulator to metallic state. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) revealed that structural rearrangement occurs (forming electrocatalytic active species) on the surface of these catalysts during electrochemical water oxidation. Extended X-ray absorption fine structure (EXAFS) curve fitting suggested the trend of surface oxidation facility for these investigated catalysts. Benefiting from the synergetic effect of intrinsic metallic state and more facile surface reorganization enabled by anions incorporated in a metal matrix, Ni3Se2 has a higher catalytic activity for electrochemical water oxidation in comparison with NiO, NiSe, and Ni. Our work suggests that both electrical transport and active species forming on the surface of precatalysts which are highly correlated with the structure of the precatalysts are critical factors determining the OER performance.