Tailoring Spin States of CuNNi 3 via d‐d Orbital Coupling for High Performance Water Splitting

ABSTRACT Against the backdrop of escalating global energy crises and environmental challenges, the development of clean and sustainable hydrogen energy has become increasingly imperative. Hydrogen production via water electrolysis is widely regarded as a promising approach due to its green and efficient characteristics. In this study, we propose an antiperovskite nitride catalyst (CuNNi 3‐ x Fe x ) to enhance its electrocatalytic performance. Specifically, electronic structure modulation was achieved through Fe doping at partial Ni sites, which effectively alters the 3d orbital electron configuration of Ni. Such electronic optimization facilitates more favorable adsorption of reaction intermediates and significantly improves electrocatalytic performance. The optimized CuNNi 2.25 Fe 0.75 catalyst exhibits markedly enhanced activity, delivering 10 mA cm −2 at overpotentials of only 63 mV for hydrogen evolution reaction (HER) and 254 mV for oxygen evolution reaction (OER). Furthermore, for overall water splitting, the catalyst requires a low cell voltage of 1.52 V to achieve the same current density. In situ Raman confirms that the change in spin state facilitates the formation of NiOOH during OER. DFT calculations reveal that Fe doping reduces reaction energy barriers and accelerates kinetics via electronic structure modulation, thereby substantially enhancing the electrocatalytic efficiency.