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

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 mg_cat ^-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.