Interfacial Confinement‐Programmed Hydrogen Spillover on Ag/CoNiS Boosts Nitrate‐to‐Ammonia Electrosynthesis

ABSTRACT Electrochemical nitrate reduction (NO 3 RR) under ambient conditions offers a sustainable route for ammonia (NH 3 ) synthesis; however, its efficiency is restricted by the kinetic mismatch between water dissociation and nitrate hydrogenation. Here, we design Ag/CoNiS heterostructures in which Ag loading density programs interfacial confinement to regulate hydrogen spillover from CoNiS water‐activation domains to Ag‐associated nitrate/nitrogen oxide (NO x ) intermediates, thereby coupling * H generation, relay, and deep nitrate hydrogenation. The optimized Ag M /CoNiS achieves an NH 3 yield of 22.31 mg h −1 cm −2 with 99.13% Faradaic efficiency. In situ Raman, distribution of relaxation times (DRT) analysis, hydrogen/deuterium (H/D) isotope experiments, and tert‐butanol (TBA) perturbation tests reveal that the confined Ag–CoNiS interface regulates interfacial water and establishes a balanced * H supply–consumption regime, thereby suppressing competing hydrogen evolution. Density functional theory (DFT) calculations further show that Ag facilitates nitrate deoxygenation, whereas excessive Ag coverage weakens Co/Ni‐centered water activation, explaining the volcano‐type activity trend. Coupling NO 3 RR with the sulfide oxidation reaction (SOR) further enables a low‐voltage NO 3 RR||SOR electrolyzer, requiring only 0.70 V at 50 mA cm −2 for energy‐saving co‐production of ammonia and sulfur.