Nickel-doped copper oxide nanoparticles synthesized by a co-precipitation method for efficient electrocatalytic synthesis of ammonia from nitrate

Abstract

In this study, we designed and constructed a nickel-doped copper oxide nanoparticle catalyst (0.1-Ni–CuO NP) and achieved high activity and selectivity for the electrocatalytic synthesis of ammonia from nitrate by adjusting the nickel-doping ratio and the electronic structure of CuO. The maximum NH₃ production rate of 1.4948 mmol h⁻¹ cm⁻² was achieved in high-concentration nitrate, with a Faraday efficiency (FE) of 92.66%. In low-concentration nitrate, a maximum ammonia production rate of 1.065 mmol h⁻¹ cm⁻² and a Faraday efficiency of 90.6% were achieved. The good performance of the catalyst is attributed to the electron transfer between nickel and copper, which regulates the electronic structure of copper oxide, increases the charge density of the active sites, and forms more oxygen vacancy defects. This is conducive to promoting the adsorption of NO₃⁻ on its surface and facilitating the breakage of N–O bonds. The introduction of Ni also enhances the ability of CuO to generate *H during the hydrogenation step. The introduction of Ni causes copper oxide to have a high porosity and an irregular particle structure, which are beneficial for increasing the specific surface area, improving the mass transfer efficiency, and enhancing the adsorption capacity for nitrates. After continuous electrolysis for ten hours, no significant decline in ammonia yield and Faraday efficiency was observed. Various characterizations indicated that the structure remained intact, suggesting excellent electrochemical and structural stability of the catalyst. This work provides insights into the design and application of efficient NO₃RR catalysts.