Asymmetric Manganese Sites in Covalent Organic Frameworks for Efficient Nitrate-to-Ammonia Electrocatalysis.
Journal:
Angewandte Chemie (International ed. in English)
Published Date:
May 12, 2025
Abstract
The electrocatalytic nitrate reduction reaction (NO3-RR) holds tremendous potential for remediating NO3- pollution in groundwater 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 low concentration of NO3- is still a challenge due to the competing hydrogen evolution reaction (HER). To address this limitation, 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 gcat.-1, exceeding the corresponding parameters of symmetric Mn sitesby 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.
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