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

Electrocatalytic nitrate reduction reaction (NO3RR), as a promising alternative to the Haber-Bosh process, provides new opportunities for ammonia (NH3) production from the environmental and energy viewpoint. However, the NH3 yield rate and selectivity for NO3RR 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 NH3. The complete conversion of nitrate (50 mg L-1 NO-3-N) was achieved at -1.5 V vs. SCE with a high NH3 yield rate (9.23 mg h-1 mg-1cat.) 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 NH3. The remaining nitrate (0.06 mg L-1) and nitrite (1 mg L-1) 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*3 to NO*2 and NH*2 to NH3, thus leading to the selective nitrate reduction to NH3.