Highly active electroreduction of nitrates to ammonia over a zeolitic imidazolium framework-derived Fe single-atom catalyst with sulfur-modified asymmetric active centers

The electroreduction of aqueous nitrate (NO3-) to ammonium is an energy-efficient process that helps protect the environment and facilitates ammonia production. However, a fine optimization of the catalyst structure containing active centers should be performed to improve the efficiencies of NO3- reduction and NH4+ production. Herein, a zeolitic imidazolate framework (ZIF)-derived sulfur-modified Fe single-atom catalyst is developed as an efficient and durable cathode material. Experimental and theoretical studies confirm the role of S-doping in modifying the electron density distribution of Fe centers, promoting the interaction between the Fe 3d orbital and O 2p orbital of NO3- and thereby enhancing its catalytic performance. A Faradaic efficiency of 93.9% for NH4+ production at  0.47 V vs. the reversible hydrogen electrode is achieved, which remains at 91.0% even after six cycles. A synergistic effect between a defect -rich support and metal atom centers can be utilized to develop a new strategy for the facile design and implementation of high-performance electrocatalysts.