Modulating the d-band center of Ni3Fe via cobalt-interface engineering for efficient bifunctional overall water splitting

NiFe alloy is regarded as a promising electrocatalyst for water splitting owing to its superior conductivity, tunable electronic structure, and abundant active sites. Nevertheless, its practical application is hindered by slow water dissociation kinetics and unfavorable adsorption of hydrogen intermediates. Herein, we develop a composite catalyst, denoted as Co/Ni 3 Fe@NC-3 through a coordination-pyrolysis route, where ZIF-67-derived Co nanoparticles are anchored on Ni 3 Fe@NC porous nanosheets. In 1 M KOH, the catalyst exhibits remarkable bifunctional activity, requiring overpotentials of 67 mV for HER and 240 mV for OER at 10 mA cm −2 . Notably, a symmetric electrolyzer based on this catalyst (Co/Ni 3 Fe@NC-3) (+||−) achieves overall water splitting at a low voltage of 1.499 V (10 mA cm −2 ), superior to the commercial Pt/C||RuO 2 benchmark (1.592 V), and sustains stable operation for 100 h at 100 mA cm −2 . In-situ electrochemical impedance spectroscopy (EIS) indicates that Co incorporation optimizes the interfacial electronic structure, leading to faster charge transfer and reduced impedance. Density functional theory (DFT) calculations and experimental results further demonstrate that Co-induced interfacial electron redistribution upshifts the d-band centers ( E d ) of Ni/Fe sites, strengthens the adsorption of H* and H 2 O, and thus synergistically enhances both HER and OER performance. This study highlights the effectiveness of interface engineering and electronic structure modulation, providing a viable strategy for designing advanced NiFe-based water-splitting catalysts.