Tuning surface electronic properties of Ni doped Cu2O catalyst toward highly selective nitrate-to-ammonia electroreduction.

The nitrate-to-ammonia electrochemical reduction reaction (NO3RR) driven by renewable energy provides a sustainable route for simultaneous wastewater treatment and green ammonia synthesis. Nevertheless, the NO3RR involves a complex multi-step proton-coupled electron transfer process, and the imbalance between proton supply and electron transfer kinetics often leads to poor selectivity toward NH3 and severe competition from the parasitic hydrogen evolution reaction (HER). Herein, a series of Ni doped Cu2O (Ni/Cu2O) catalysts with a well-defined cubic morphology are developed via a facile one-pot reduction strategy to overcome these limitations. Theoretical calculations demonstrate that Ni incorporation effectively modulates the electronic structure of Cu2O, facilitating water dissociation to generate sufficient surface *H species and thereby accelerating the hydrogenation of nitrogen-containing intermediates. Meanwhile, enhanced orbital interactions between the catalyst surface and *NO intermediates promote the *NO2 → *NO conversion, leading to improved reaction kinetics and selectivity. The optimized Ni/Cu2O catalyst with enriched surface hydroxyl/water chemisorb amount and abundant catalytic active sites achieves a high NH3 faradaic efficiency (FE) of 91.11 ± 3.43% and an NH3 yield rate of 7.81 ± 0.53 mg h-1 mgcat -1 at -0.9 V vs. RHE and reduced charge-transfer resistance, outperforming pristine Cu2O. This work highlights the synergistic roles of facet engineering and electronic modulation, providing a rational framework for the design of high-performance, earth-abundant electrocatalysts for sustainable nitrate-to-ammonia conversion.