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

The electrocatalytic nitrate reduction reaction (NO₃ ^-RR) holds tremendous potential for remediating NO₃ ^- pollution while enabling clean ammonia (NH₃) production. However, most catalysts achieve high conversion efficiency relying on high NO₃ ^- concentrations. How to catalyze the NO₃ ^-RR with a low concentration of NO₃ ^- 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 NO₃ ^-RR at a low NO₃ ^- concentration of 2 mg mL^-1. 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% NH₃ selectivity and a maximum NH₃ yield rate of 1927 mmol h^-1 g_cat. ^-1, 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.