Boosting the selectivity and efficiency of nitrate reduction to ammonia with a single-atom Cu electrocatalyst

Electrochemically reducing nitrate to ammonia provides an efficient pathway to alleviate nitrate pollution and produce ammonia. However, it remains challenging to regulate the low selectivity of ammonia production and the sluggish kinetics of nitrate-to-ammonia conversion. Here, a single-atom Cu catalyst is prepared for selective and efficient nitrate reduction to ammonia, achieving an ammonia production rate of 2602 μg cm-1h−1 (5302 μg h−1 mgcat.-1) at −1.1 V (vs. RHE) with 87.2% Faradic efficiency and 94.1% ammonia selectivity in 0.01 M PBS buffer solution (pH about 7, containing 500 mg L-1 nitrate-N), outcompeting to most of the reported catalysts. DFT calculations reveal that the CuN4 site facilitates both the *NO formation and the subsequent ammonia generation for nitrate reduction in a complete downhill free energy pathway, thus providing the remarkable activity and selectivity of ammonia production for the single-atom Cu catalyst superior to the Cu nanoparticle catalyst. This study provides a strategy for designing electrocatalysts in efficient and selective ammonia production via nitrate reduction.