Coordination environment-tailored electronic structure of single atomic copper sites for efficient electrochemical nitrate reduction toward ammonia†

Continuously and finely tuning the electronic structure of metal active sites is essential to maximize the nitrate reduction reaction (NO₃⁻RR) performance towards ammonia (NH₃) and elucidate the reaction mechanism. Here, we employ single atomic Cu–N–C as a model system and develop a robust strategy to finely tailor the electronic structure of Cu via engineering of both the first and second coordination shells (CSs) with B atoms. It is found that the first and second CS modification of B induces two opposite effects: the first modification leads to tension strains of Cu–N bonds and the decreased valence state of Cu, whereas the second CS modification leads to compressive strains and the increased valence state. Thanks to the bidirectional regulatory mechanism induced by B, we continuously tune the electronic structure of Cu to reach the top of adsorption volcano curves, thereby concurrently reducing the energy barrier of the NO₃⁻RR and water dissociation step. Consequently, the optimized Cu–N₄B₂ catalyst displays superior NO₃⁻RR performance to other Cu–N–C catalysts. Clearly, this work offers a guideline to design efficient NO₃⁻RR electrocatalysts via finely tuning metal electronic structures.