High‐Valence Metal‐Driven Electronic Modulation for Boosting Oxygen Evolution Reaction in High‐Entropy Spinel Oxide

Abstract High‐entropy spinel oxides (HESOs) are a promising class of electrocatalysts whose material properties and catalytic activity can be finely tuned by controlling the elemental composition. Although numerous HESOs are already reported, their compositions are primarily limited to the first‐row transition metals. Herein, the synthesis of a high‐entropy spinel (CrFeCoNiMo) 3 O 4 nanosheet (HEO‐NS) and its application as oxygen evolution reaction (OER) catalyst are reported. The high‐entropy spinel displays a low overpotential of 255.3 mV at a current density of 10 mA cm −2 and excellent stability, outperforming the IrO 2 benchmark. Careful analysis with X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption spectroscopy (XAS) reveals that the incorporation of high‐valence Cr and Mo can activate the lattice oxygen by weakening the metal–oxygen bond and promoting the lattice oxygen mechanism (LOM). Furthermore, the catalyst can achieve a high current density of 1 A cm −2 at 1.71 V in a lab‐scale electrolyzer, demonstrating the potential of HESOs for practical application.