Electrochemical Surface Reconstruction of CrMnFeNi Medium-Entropy Alloys for Enhanced Oxygen Evolution Reaction

The oxygen evolution reaction (OER) catalyzed by earth-abundant, noble metal-free elements is a promising and economically viable process for sustainable water splitting. However, achieving high activity and stability remains challenging, where surface engineering has emerged as one of the most efficient strategies to modulate surface composition, electronic structure, and catalytic kinetics. Herein, we report that electrochemical cyclic voltammetry activation (CV-activation) can serve as an efficient surface reconstruction technique to induce the creation of reactive surface chemical states in the CrMnFeNi medium-entropy alloys (MEAs). The surface of the CrMnFeNi MEAs is converted into a metal oxide MO_x (M = Cr, Mn, Fe, and Ni) layer after 500 cycles of CV-activation, which leads to enhanced electrocatalytic OER performance, including a lower observed overpotential of 248 ± 1 mV at a current density of 10 mA cm^-2, a small Tafel slope of 60.6 ± 0.1 mV dec^-1, and a stability of 20 h of sustained reaction when conducted in a 1.0 M KOH electrolyte. The surface evolution mechanism was further elucidated through X-ray photoelectron spectroscopy (XPS) characterization of the metal valence states before and after CV-activation, revealing that the formation of high-valence metal species is crucial for enhancing catalytic performance and stability in the OER. This study indicates the valuable potential of multicomponent alloys as electrocatalysts and offers some design strategies for the enhancement of OER performance.