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.