Localized Active H* Enrichment by Cobalt Molecular Catalysts for Enhanced Electrocatalytic Nitrate Reduction
Xindie Jin, Libo Sun, Xingyu Wang, Xingyu Wang, Ruixue Wang, Liting Yan, Adrian C. Fisher, Jong‐Min Lee, Xin Wang, Xin Wang
Abstract
Abstract Electrochemical nitrate reduction (NO 3 − RR) offers a sustainable route for ammonia (NH 3 ) synthesis, simultaneously enabling pollutant remediation and resource recovery. The efficiency of NO 3 − RR relies on regulating the hydrogenation behaviors of active sites to drive the stepwise reduction of nitrate species. Herein, we report a molecular catalyst, cobalt tetrapyrazinoporphyrazine (CoPhz) supported on carbon nanotubes (CoPhz/CNT) that achieves outstanding NO 3 − RR performance through local active H* enrichment. In neutral electrolyte, CoPhz/CNT attained a peak NH 3 Faradaic efficiency (FE) of 93% and a yield rate of 8347.9 µg h −1 cm −2 , outperforming the conventional cobalt phthalocyanine (CoPc) benchmark. CoPhz/CNT exhibited exceptional stability for over 170 h at 50 mA cm −2 in a flow cell. Operando studies and theoretical calculations reveal that nitrogen atoms in the macrocycle modulate the electronic structure of the cobalt center, promoting H* generation and enrichment, as well as facilitating efficient intermediates conversion with low energy differences, leading to superior NO 3 − RR efficiency. Furthermore, the practical utility of CoPhz/CNT in a Zn–NO 3 − battery achieved an excellent power density of 14.5 mW cm −2 . This work demonstrates that molecular engineering of macrocyclic catalysts is an effective strategy to tailor hydrogenation capability for enhanced NO 3 − RR and other hydrogenation reactions.