Asymmetric Manganese Sites in Covalent Organic Frameworks for Efficient Nitrate-to-Ammonia Electrocatalysis.

The electrocatalytic nitrate reduction reaction (NO RR) holds tremendous potential for remediating NO pollution while enabling clean ammonia (NH) production. However, most catalysts achieve high conversion efficiency relying on high NO concentrations. How to catalyze the NO RR with a low concentration of NO is still a challenge due to the competing hydrogen evolution reaction (HER). Herein, we constructed a novel asymmetric isolated Mn atom based on N-coordination covalent organic framework (COF) (ImPy-COF-Mn), for efficient NO RR at a low NO concentration of 2 mg mL. This bidentate-coordinated COF featured a robust and chemically stable framework, while the synergistic interaction between asymmetric imine N and pyridine N modified the charge distribution of Mn atoms to optimize catalytic efficiency. ImPy-COF-Mn demonstrated remarkable catalytic performance, with 95.64% NH selectivity and a maximum NH yield rate of 1927 mmol h g , exceeding the corresponding parameters of symmetric Mn sites by factors of 1.27 and 1.41, respectively. In situ ATR-FTIR measurements and theoretical calculations revealed that the asymmetric isolated Mn facilitated a reduction in the energy barrier for *NO-to-*NOH conversion, and thus contributed to higher activity and selectivity.