Acid-Etched Co-Vacancy-Tunable CoFeP/N,P-Codoped Carbon Nanocages for Highly Efficient Alkaline Water Electrolysis AITranslate

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Efficient and durable bifunctional electrocatalysts are vital for scalable water electrolysis. Here, we realize cobalt-vacancy (Covac) engineering in CoFeP supported on N,P-codoped carbon nanocages (Co1-vacFeP/NPC) through a simple route comprising a CoFe Prussian blue analog precursor, phosphidation–pyrolysis, tannic-acid etching, and a second phosphidation. Varying the tannic-acid concentration tunes Covac density. Density functional theory (DFT) shows that Covac acts as a proton-capture center in hydrogen evolution reaction (HER), accelerating OH− dissociation and lowering ΔGH*, while upshifting the d-band center of neighboring Co in oxygen evolution reaction (OER) to weaken Co–O bonding and reduce the barrier of the rate-determining step (*OH → *O). Benefiting from vacancy-induced electronic modulation, the integrated FeP4/CoP2 heterostructure, and the conductive NPC support, the optimized catalyst delivers overpotentials of 102 mV (HER) and 245 mV (OER) at 10 mA cm−2 in 1.0 M KOH, surpassing 20% Pt/C (120 mV) and RuO2 (326 mV), respectively. A two-electrode electrolyzer using the same catalyst at both electrodes requires only 1.555 V at 10 mA cm−2 and exhibits a cell-voltage increase of just 7 mV after 24 h, outperforming a Pt/C||RuO2 device. This work establishes a facile strategy to create metal-cation vacancies and provides mechanistic guidance for designing multi-vacancy heterostructure-coupled catalysts for efficient alkaline water electrolysis.