Manipulating interfacial built-in electric field of heterostructure catalysts to promote overall water splitting in alkaline.

The strategic construction of built-in electric fields (BIEF) through heterostructure engineering has emerged as a promising avenue for enhancing the intrinsic catalytic activity in dual-functional water electrolysis. In this work, we develop an innovative in-situ topological reconstruction strategy to fabricate phosphorus-defect-enriched NiCoP@NiFe LDH p-n heterojunction architectures on nickel foam (denoted as NiCoP@NiFe LDH/NF), establishing a quantitative structure-activity relationship between BIEF intensity modulation and catalytic performance enhancement. The introduced phosphorus vacancies at the heterointerface synergistically amplify the BIEF strength compared to defect-free counterparts, as evidenced by advanced characterizations, which orchestrates three critical catalytic enhancements: (i) accelerated interfacial charge transfer kinetics (charge transfer resistance reduced by 48 %), (ii) optimized adsorption/desorption energetics for reactive intermediates (ΔG = -0.12 eV for HER), and (iii) precise tuning of transition metal d-band centers toward optimal positions. The resultant catalyst exhibits exceptional bifunctional activity with ultralow overpotentials of 36 mV (HER) and 220 mV (OER) at 10 mA∙cm, surpassing benchmark Pt/C (43 mV) and RuO (265 mV) catalysts. Remarkably, the assembled alkaline electrolyzer achieves a record-low cell voltage of 1.50 V at 10 mA∙cm with unprecedented durability (∼200 h). Through multiscale density functional theory (DFT) simulations, we systematically reveal that the BIEF amplification from defect-heterojunction synergy induces charge redistribution at the atomic level, thereby creating optimal dual-active sites with balanced H* and O-containing intermediate adsorption. This work establishes a novel paradigm for designing high-performance electrocatalysts through defect-mediated BIEF engineering while providing fundamental insights into the quantum-level regulation of catalytic processes.