Intensifying Interfacial Reverse Hydrogen Spillover for Boosted Electrocatalytic Nitrate Reduction to Ammonia

Rational regulation of active hydrogen (*H) behavior is crucial for advancing electrocatalytic nitrate reduction reaction (NO3RR) to ammonia (NH3), yet in‐depth understanding of the *H generation, transfer, and utilization remains ambiguous, and explorations for *H dynamic optimization are urgently needed. Herein we engineer a Ni3N nanosheet array intimately decorated with Cu nanoclusters (NF/Ni3N‐Cu) for remarkably boosted NO3RR. From comprehensive experimental and theoretical investigations, the Ni3N moieties favors water dissociation to generate *H, and then *H can rapidly transfer to the Cu via unique reverse hydrogen spillover mediating interfacial Ni‐N‐Cu bridge bond, thus increasing *H coverage on the Cu site for subsequent deoxygenation/hydrogenation. More impressively, such intriguing reverse hydrogen spillover effect can be further strengthened via elegant engineering of the Ni3N/Cu heterointerface with more intimate contact. Consequently, the NF/Ni3N‐Cu with Cu nanoclusters intimate anchoring presents record NH3 yield rate of 1.19 mmol h‐1 cm‐2 and Faradaic efficiency of 98.7% at −0.3 V vs. RHE, being on par with the state‐of‐the‐art ones. Additionally, with NF/Ni3N‐Cu as the cathode, a high‐performing Zn‐NO3− battery can be assembled. This contribution illuminates a novel pathway to optimize *H behavior via distinct reverse hydrogen spillover for promoted NO3RR and other hydrogenation reactions.