Modulating the electronic state of Ni active sites in medium-entropy borides for enhanced water oxidation performance.

Medium-entropy materials (MEMs) have attracted significant attention for electrocatalytic water oxidation due to their exceptional physicochemical properties. However, limited efforts have been made to elucidate the origins of their extraordinary activity and the intricacies of their atomic arrangements. Herein, we present a novel magnetic field-assisted interface co-assembly approach for synthesizing CoFeNiMnB nanochains (Mn-MEB), effectively overcoming the immiscibility challenges associated with combining multiple metal elements. The resulting Mn-MEB catalyst exhibits remarkably enhanced oxygen evolution reaction (OER) activity, achieving a low overpotential (η = 280 mV), a small Tafel slope (76.7 mV dec), and excellent stability, thereby outperforming conventional catalysts. Structural characterization and theoretical calculations reveal that synergistic electronic coupling modulates the active Ni centers, optimizing intermediate adsorption energies. Meanwhile, in-situ impedance spectroscopy and potentiodynamic polarization curves revealed that the increase in configurational entropy accelerated surface reconstruction and mitigated phase segregation and transformation, thereby enhancing structural stability. When employed as the anode in an alkaline exchange membrane water electrolyzer, the Mn-MEB catalyst achieves a low cell voltage of 1.58 V at 10 mA cm and exhibits exceptional stability, sustaining operation for over 130 h. The insights gained into the interplay among composition, activity, and stability in medium-entropy coordination systems provide valuable guidance for the strategic design of catalysts tailored to diverse electrochemical processes.