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

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 NOx, 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.