Electronic engineering of CoSe/FeSe₂ hollow nanospheres for efficient water oxidation

First-row non-precious metal-based catalysts are widely studied and recognized as potential substitutes for precious metal-based catalysts in the oxygen evolution reaction (OER) for hydrogen generation but their application remains challenging. In this study, a unique class of Co-Fe selenide hollow nanospheres (CoSe@FeSe2) is well-designed through a facile hydrothermal method. The in situ formed hybrid composites possess numerous interfaces allowing partial electron transfer via O2- bridges to optimize the adsorption feature of the reaction intermediates, *OH, *O, and *OOH, on the catalysts. The collected surface valence band spectra evidence the optimization of the intermediate adsorption and active sites. The as-synthesized CoSe@FeSe2 exhibits excellent OER activity with a low overpotential of 281 mV to drive a current density of 10 mA cm-2 and a low Tafel slope of 34.3 mV dec-1 in an alkaline electrolyte. Additionally, the advanced catalyst also shows super stability with negligible current density decay after 12 h. This work presents a prototype for the fabrication of highly efficient electrocatalysts using an electronic engineering strategy.