Copper single-atom catalyst as a high-performance electrocatalyst for nitrate-ammonium conversion.

Electrocatalytic nitrate reduction reaction (NORR), as a promising alternative to the Haber-Bosh process, provides new opportunities for ammonia (NH) production from the environmental and energy viewpoint. However, the NH yield rate and selectivity for NORR are still limited due to the lack of efficient electrocatalysts. Herein, we demonstrate an active and selective copper single-atom catalyst (Cu-N-C) for nitrate reduction to NH. The complete conversion of nitrate (50 mg L NO-N) was achieved at -1.5 V vs. SCE with a high NH yield rate (9.23 mg h mg) and selectivity (94%). Remarkably, Cu-N-C dramatically inhibited the formation of toxic nitrite and double-nitrogen products due to the enhanced nitrite adsorption and restrained N-N coupling that led to nitrate deep reduction to NH. The remaining nitrate (0.06 mg L) and nitrite (1 mg L) fully meet the drinking-water standards. Density functional theory simulations reveal that the single-site nature of Cu-N-C facilitated the reduction of HNO* to NO* and NH* to NH, thus leading to the selective nitrate reduction to NH.