Synergistic Cu2O@Ni(OH)2 Core–Shell Electrocatalyst for High-Efficiency Nitrate Reduction to Ammonia

Abstract

The electrocatalytic reduction reaction of nitrate (NO₃RR) is anticipated to convert nitrogen-containing pollutants into valuable ammonia products. Copper-based catalysts have received great attention because of their good performance in the NO₃RR due to the strong binding energy with *NO₃ intermediates. However, the poor H₂O dissociation ability of Cu is unable to provide H^• in time for the hydrogenation reaction of NO_x, thus hindering the electroreduction of the NO₃^–. Herein, we designed a shell–core nanocube electrocatalyst Cu₂O@Ni(OH)₂-x (x represents the molar ratio of Ni/Cu) using the liquid phase reduction combined with the etching and precipitation method for electrocatalytic NO₃RR. Due to the synergistic effect between the strong nitrate activation ability of Cu and the excellent H₂O dissociation ability of Ni(OH)₂, Cu₂O@Ni(OH)₂-3.3% shows an impressive ammonia yield rate (557.9 μmol h^–1 cm^–2) and Faradaic efficiency (97.4%) at −0.35 V vs. RHE. Operando Raman and Auger electron spectroscopy observe the reduction of Cu₂O to Cu during the NO₃RR process. Density functional theory calculations combined with electron paramagnetic resonance analysis reveals that Ni(OH)₂ can lower the activation energy barrier of H₂O dissociation, thereby promoting the generation of H^• and accelerating the hydrogenation of *NO during the NO₃RR. This research provides an efficient Cu-based catalyst for reducing NO₃^– and may motivate the development of effective ammonia electrocatalysts for further experimentation.