Low-coordinated Cu-Ni edge sites in bimetallic aerogels for boosting electrochemical nitrate-to-ammonia conversion

Cu-based electrocatalysts hold significant potential for ammonia (NH₃) production through the electrochemical nitrate reduction reaction (NO₃^--RR). Optimizing the adsorption of intermediates by tailoring the electronic structure is crucial for enhancing NO₃^--RR performance. In this study, we developed small-sized Cu-Ni bimetallic aerogels (Cu-Ni MAs) featuring abundant unsaturated active edge sites to serve as efficient catalysts for NO₃^--RR. Compared to Cu-Ni nanoparticles (NPs), these Cu-Ni MAs demonstrated superior intrinsic activity. In a 0.5 M Na₂SO₄ solution containing 0.01 M NaNO₃, the optimized Cu-Ni 3:1 MAs achieved a NH₄⁺ yield of 3.30 mg h^-1 mg_cat^-1 with a Faradaic efficiency (FE) of 80.1 % at -0.4 V (vs. RHE), while maintaining a low NO₂^- byproduct yield of 0.69 mg h^-1mg_cat^-1. Furthermore, the electrochemical active surface area (ECSA)-normalized NH₄⁺ yield of the Cu-Ni MAs was twice that of Cu-Ni NPs. Isotopic labeling experiments with ¹⁵N confirmed that the produced ammonia originated from nitrate. DFT calculations revealed that the Cu-Ni edge sites possessed modified electronic properties, characterized by an elevated d-band center and reduced work function. These edge sites exhibited enhanced adsorption of *NO₃ and *NO₂ intermediates and greater electron availability, contributing to the improved catalytic performance.