Unveiling a Surface‐Bulk Electronic Dichotomy in Co ₃ O ₄ /ZnO Heterojunctions for Enhanced Electrocatalytic Nitrate‐to‐Ammonia Conversion

Constructing heterojunctions is a powerful strategy to optimize electrocatalysts, yet interfacial electronic reconstruction is often oversimplified as unidirectional charge transfer. Herein, we report Co 3 O 4 /ZnO heterostructures that exhibit a unique surface‐bulk electronic dichotomy for nitrate reduction to ammonia. Surface‐sensitive XPS reveals electron deficiency at Co sites, while bulk‐sensitive XANES and DFT calculations demonstrate net electron accumulation within the Co 3 O 4 lattice. This distinctive feature, arising from interfacial Co─O─Zn bonding and enriched oxygen vacancies, establishes a “surface‐capture and bulk‐activation” motif in which electron‐deficient surface Co sites enhance nitrate adsorption, while electron‐enriched bulk Co centers optimize *H and *NOH adsorption, thereby lowering the rate‐determining step barrier to 0.41 eV. The optimized Co 3 O 4 /ZnO catalyst achieves a Faradaic efficiency of 98.36% at −0.25 V (vs. RHE) and a NH 3 yield of 9.35 mg h −1 cm −2 . Furthermore, a membrane electrode assembly flow cell integrating glycerol oxidation at the anode delivers a current density of 600 mA·cm −2 at 2.5 V with stable operation over 40 h. This work unveils surface‐bulk electronic decoupling as a new paradigm for heterojunction design, demonstrating both exceptional catalytic performance and practical application potential for energy‐efficient ammonia electrosynthesis.