Interface Reconstruction Induced by Rare-Earth Incorporation Stabilizes High-Coordination Cu+ Sites for Efficient Electrochemical Nitrate Reduction to Ammonia

Abstract The electrochemical nitrate reduction reaction (eNO3–RR) represents a promising route for simultaneous wastewater treatment and sustainable ammonia synthesis. While Cu2O catalysts featuring electron-deficient Cu+ sites have been widely studied for eNO3–RR, their practical implementation is hindered by self-reduction and structural instability. Constructing Cu–O–M interfacial sites, which enhance charge transfer and stabilize catalytic sites, presents an effective strategy for addressing these challenges. Here, we report a La incorporation strategy to create Cu2O–LayO heterointerfaces (Cu1La4) for highly efficient conversion of NH3. Experimental and theoretical studies indicate that the high-coordinated Cu+ active sites at the Cu2O/La2O2(CO3) interface, together with the steric hindrance introduced by La incorporation, optimize the adsorption energy of key intermediates, thereby circumventing the high energy barrier associated with the *NH3→NH3 transition on traditional low-coordination Cu+ sites. Furthermore, the covalent Cu–O–La interfacial bonding inhibits Cu+ reduction and stabilizes the catalytic system. The optimized Cu1La4 catalyst demonstrates outstanding eNO3–RR performance, achieving a Faradaic efficiency (FE) of 94% at –0.6 V and an NH3 yield rate of 234 μmol h–1 cm–2. Significantly, the Cu1La4 catalyst exhibited exceptional stability in a membrane electrode assembly (MEA), sustaining ∼7.8 mg h–1 cm–2 NH3 production and high FE of ∼85% over 150 h at 400 mA.