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

The electrocatalytic reduction reaction of nitrate (NO 3 RR) 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 NO 3 RR due to the strong binding energy with *NO 3 intermediates. However, the poor H 2 O dissociation ability of Cu is unable to provide H • in time for the hydrogenation reaction of NO x, thus hindering the electroreduction of the NO 3 – . Herein, we designed a shell–core nanocube electrocatalyst Cu 2 O@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 NO 3 RR. Due to the synergistic effect between the strong nitrate activation ability of Cu and the excellent H 2 O dissociation ability of Ni(OH) 2, Cu 2 O@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 Cu 2 O to Cu during the NO 3 RR process. Density functional theory calculations combined with electron paramagnetic resonance analysis reveals that Ni(OH) 2 can lower the activation energy barrier of H 2 O dissociation, thereby promoting the generation of H • and accelerating the hydrogenation of *NO during the NO 3 RR. This research provides an efficient Cu-based catalyst for reducing NO 3 – and may motivate the development of effective ammonia electrocatalysts for further experimentation.