Interfacial Synergy Triggered Intrinsic Tandem Catalysis for High-Efficiency Electrochemical Nitrate Reduction to Ammonia

Abstract Electrochemical nitrate reduction reaction (NO3RR) has emerged as a sustainable circular-economy approach that enables simultaneous remediation of nitrate-contaminated wastewater and green ammonia synthesis. However, practical implementation of NO3RR is severely hindered by complicated multi-proton-electron transfer processes, undesirable nitrite accumulation, and competing hydrogen evolution reactions. While bimetallic heterostructured tandem catalysts hold great potential to address these issues, conventional spatially separated dual-site configurations still suffer from sluggish intermediate relay, mismatched reaction kinetics, and uncontrollable nitrite desorption. Herein, we fabricate a nanoparticle-assembled needle-like CuO/Co3O4 heterostructure and propose an interfacial synergy-triggered intrinsic tandem catalysis strategy. The optimized CuO/Co3O4 (1:1) delivers an NH3 yield of 1.06 ± 0.07 mmol h–1 mg–1 (0.53 ± 0.035 mmol h–1 cm–2) at –0.9 V vs RHE and a maximum Faradaic efficiency of 95.57 ± 1.15% at –0.8 V vs RHE, superior to monometallic counterparts and physical mixtures. Heterointerfaces modulate intermediate (*NO3, *NO2, *H) adsorption and boost in situ active-hydrogen production to match cascade reaction kinetics. Combined operando characterizations and density functional theory calculations demonstrate that the heterointerface efficiently suppresses excessive *NO2 desorption, strengthens nitrite intermediate trapping, and enriches surface-active hydrogen species, resolving the kinetic mismatch that plagues traditional dual-site catalytic systems. This work establishes an interface-dominated pathway for the design of high-efficiency intrinsic tandem catalysts, breaking through the performance bottleneck of conventional simple phase-mixing strategies.