Modulating NO3–/H2O Competitive Adsorption via a Defective ZnO/Cu Single–Atom for Ammonia Electrosynthesis

Abstract Electrocatalytic nitrate reduction reaction (NitRR) offers a sustainable route for nitrate removal and ammonia production, yet its efficiency is limited by sluggish multistep kinetics and competitive hydrogen evolution. Herein, a CuSA–ZnO@CW electrocatalyst was constructed by stabilizing O–coordinated Cu single atoms on defective ZnO supported by carbonized wood. The conductive wood-derived scaffold facilitates mass/electron transport, while the defective ZnO/Cu–O3 interface regulates local adsorption competition between NO3– and H2O. CuSA–ZnO@CW delivers an NH3 yield of 3561.9 μg h–1 cm–2 and a Faradaic efficiency of 97.07% at –1.1 V vs RHE, with stable performance over 36 cycles. Mechanistic studies reveal that ZnO preferentially accommodates interfacial H2O, whereas Cu–O3 sites selectively activate NO3– and promote NOX intermediate conversion, thereby reducing the free-energy requirement of the potential-determining step and suppressing hydrogen evolution reaction (HER). This work presents a defective oxide–regulated single–atom interface for selective NO3– to NH3 conversion.