Copper-Nickel Bimetallic-Doped Nanospinel for Efficient Electrochemical Reduction of NO to NH₃

Electrocatalytic reduction of nitric oxide (eNORR) represents a promising and sustainable resource strategy. The process is effective at both mitigating anthropogenic air pollution and producing ammonia (NH₃) in a manner that is environmentally sustainable and reliant on renewable energy sources. In this study, a series of Cu, Ni metal A-site doped nanospinel composites Cu_xNi_1-xCo₂O₄ (x = 0, 0.5, 0.9, 1) were synthesized as highly efficient electrocatalysts for NO reduction. The experimental results on catalytic activity showed that Cu_0.5Ni_0.5Co₂O₄ exhibited a maximum Faraday efficiency (FE) of 92.73% at −0.9 V vs reversible hydrogen electrode (vs RHE), with NH₃ production rate of 99.12 mmol g^-1 h^-1 at room temperature. Microscopic characterization indicated that the distinctive nanorod structure effectively increased the surface area, promoted electron/ion transport, and exposed more active sites. X-ray photoelectron spectroscopy (XPS) results demonstrated that the interaction between the A-site metals could enhance charge transfer and inhibit the hydrogen evolution reaction (HER). The theoretical analysis comprehensively demonstrated that the enhanced catalytic efficiency of Cu_0.5Ni_0.5Co₂O₄ was primarily attributed to the incorporation of Cu metal doping, which facilitated a modification in the electronic structure of NiCo₂O₄. Furthermore, the synergistic effect between Cu and Ni metal sites significantly facilitated the stable adsorption of the reaction intermediate ^*NHO on the catalyst surface. This work offers a theoretical guidance that facilitates the efficient and environmentally friendly synthesis of NH₃ and the design of spinel catalysts exhibiting superior performance.