Low-Coordinated Cu-Ni Edge Sites in Bimetallic Aerogels for Boosting Electrochemical Nitrate-to-Ammonia Conversion

Abstract

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.