Crystalline–Amorphous Schottky Junction Modulates d/p-Orbital Center Proximity for Efficient Overall Water Splitting at Industrial Current Density

Constructing efficient and durable bifunctional electrocatalysts for overall water splitting (OWS) under industrial current densities remains a critical challenge. Herein, we report a crystalline–amorphous (C–A) Schottky junction catalyst, NiFe(OH)x/Fe7S8/IF, featuring a nanosphere-assembled hierarchical architecture synthesized via a two-step in situ growth strategy. The hybrid integration of conductive Fe7S8 nanorods and amorphous NiFe(OH)x nanosheets generates a robust C–A heterointerface. Mechanistic investigations reveal that the built-in electric field (BIEF) at the Schottky interface not only narrows the band gap of NiFe (oxy)hydroxide to improve charge transport, but also modulates the adsorption behavior of reaction intermediates by tuning the d/p-band center proximity (Δεd–p) of surface reaction sites. First-principles calculations demonstrate that Δεd–p serves as a reliable electronic descriptor for optimizing HER and OER pathways of NiFe (oxy)hydroxide-Fe7S8 heterointerface via balancing H adsorption and weakening OOH binding, respectively. Benefiting from these unique electronic regulations, the resulting catalyst exhibits exceptional bifunctional electrocatalytic performance, requiring overpotentials of only 359 mV for the hydrogen evolution reaction (HER) at 1 A cm–2 and 380 mV for the oxygen evolution reaction (OER) at 500 mA cm–2. When integrated into a two-electrode electrolyzer, the NiFe(OH)x/Fe7S8/IF couple achieves a low cell voltage of 1.42 V at 10 mA cm–2 and sustains 1 A cm–2 over 300 h with minimal current density decay. This work sheds light on a generalizable interfacial design strategy and introduces Δεd–p as a conceptual framework for the rational design of cost-effective, high-performance water-splitting electrocatalysts.