Metastable Phase Cu with Optimized Local Electronic State for Efficient Electrocatalytic Production of Ammonia from Nitrate

Abstract Electrocatalytic nitrate (NO 3 − ) reduction reaction (NITRR) is an inspiring route for ammonia (NH 3 ) synthesis at ambient condition. The metallic Cu‐based material with low cost and high activity is one of the most promising electrocatalysts for NITRR. However, due to the weaker atomic H * ‐providing capacity, the produced intermediate—nitrite tends to accumulate on its surface, leading to unsatisfactory NH 3 selectivity and Faradic efficiency (FE). Herein, a novel and facile O 2 /Ar plasma oxidation and subsequent electro‐reduction strategy is developed to synthesize a kind of metastable phase Cu. Excitingly, the metastable phase Cu demonstrates superior NITRR performance to conventional phase Cu with high NH 4 + selectivity (97.8%) and FE (99.8%). Density function theory (DFT) calculations reveal that the upshift of the d ‐band center to near the Fermi level in metastable phase Cu contributes to the enhanced activity, while the relatively strong adsorption of H * facilitates the conversion from NO 2 * /NO * to NOOH * /NOH * and thus ensures high selectivity and FE. Furthermore, when evaluated as cathode material in Zn‐NO 3 − battery, high power density (7.56 mW cm −2 ) and NH 4 + yield (76 µmol h −1 cm −2 ) are achieved by the metastable phase Cu‐based battery.