CuO/Sm₂CuO₄ heterointerfaces with Sm-derived Lewis acid sites for efficient nitrate-to-ammonia electroreduction

The high-rate and device-level performance of Cu-based catalysts for electrocatalytic nitrate reduction to ammonia (NO₃RR) remains constrained by sluggish hydrogenation of downstream nitrogen-containing intermediates, inefficient utilization of surface active hydrogen (H), and unstable Cu valence states. Herein, rare-earth samarium is introduced into a Cu-based oxide system to construct an intimately coupled CuO/Sm₂CuO₄ heterointerface through a stepwise precipitation-calcination strategy. Interfacial Cu-Sm coordination induces electron redistribution and lowers the catalyst work function, while Sm-derived Lewis acid sites promote nitrate adsorption and activation; together, these effects facilitate electron transfer and H-mediated hydrogenation of nitrate-derived intermediates. Consequently, the optimized Cu₁Sm₁ catalyst achieves a maximum NH₃ faradaic efficiency of 92.82% and an NH₃ yield rate of 454.44 μmol h^-1 cm^-2 at -0.7 V vs. RHE. When integrated into a membrane-electrode assembly, Cu₁Sm₁ reaches a current density of 1000 mA cm^-2 at approximately 2.8 V and sustains operation for over 150 h at 500 mA cm^-2, with the NH₃ faradaic efficiency remaining above 80%. This work demonstrates that rare-earth-induced heterointerface engineering can simultaneously regulate nitrate adsorption, interfacial proton transfer, and intermediate hydrogenation, providing an effective strategy for developing high-rate and durable Cu-based NO₃RR electrocatalysts.