The Influence of Anion Effects on the Morphology of Copper-Based Hydroxides and Their Electrocatalytic Performance in the Reduction of Nitrite to Ammonia

Copper-based hydroxides are attracting increasing attention in the electrocatalytic reduction of nitrite to ammonia (NO2RR) due to their strong redox activity and charge storage capacity. In this work, anions F– and Cl– were introduced into copper hydroxide via a hydrothermal method, resulting in the successful preparation of copper hydroxyfluoride with stacked flower-like nanosheets and copper hydroxychloride with hexagonal platelet shapes. Among these, copper hydroxyfluoride exhibits the highest activity. The results of XPS characterization and electrochemical active area testing indicate that the introduction of F– alters the electronic structure of the copper hydroxide salt, which enhances the adsorption capacity for NO2– and simultaneously suppresses the hydrogen evolution reaction. As a result, the electrocatalytic performance is improved by 1.5 times compared to neat copper hydroxide. In a 0.5 M Na2SO4 + 0.05 M NaNO2 electrolyte, it achieves a high ammonia production rate of 13.83 mg h–1 mgcat–1 and a Faradaic efficiency of 91.47%. This demonstrates that the anion effect can be a good strategy for enhancing the electrocatalytic performance of copper hydroxides, offering new avenues for the design and development of high-performance NO2RR catalytic materials.