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

Electrocatalytic nitrate (NO3-) reduction reaction (NITRR) is an inspiring route for ammonia (NH3) 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 NH3 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 NH4+ 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 NO2*/NO* to NOOH*/NOH* and thus ensures high selectivity and FE. Furthermore, when evaluated as cathode material in Zn-NO3- battery, high power density (7.56 mW cm(-2)) and NH4+ yield (76 mu mol h(-1) cm(-2)) are achieved by the metastable phase Cu-based battery.