Enrichment of Cu Ions on Fe₃O₄ Surface to Promote NO_x− Adsorption for Efficient Ammonia Production

The electrocatalytic nitrate reduction reaction (eNO₃−RR) represents a promising approach for the sustainable production of ammonia and the alleviation of environmental nitrate pollution. The doping of metal oxides with other atoms is capable of regulating the physicochemical properties of catalysts for electrochemical applications. Nevertheless, no report in the current literature has addressed the effect of the position of heteroatom doping on eNO₃−RR. In this study, the doping positions of copper ions are modulated to investigate their interfacial interactions, with the objective of enhancing the performance of the eNO₃−RR. When Cu is confined within the lattice, it regulated the electronic structure of Fe₃O₄, inducing an upward shift of the d-band centre of Fe and adjusting the strength of adsorption to NO₃−. Conversely, Cu ions anchored on the surface exerted little influence on the electronic structure, and the surface-adsorbed Cu served as a dynamically active site with a relatively low coordination number, resulting in a strong coordination with NO₃−, which could effectively activate the reactants. This work offers a novel guideline for the design of electrocatalysts in eNO₃−RR.