Defect-Enriched Cobalt-Based Coordination Polymers for Selective and Efficient Nitrate Electroreduction to Ammonia

Abstract

Electrocatalytic nitrate reduction to ammonia (NRA) offers an arousing route for converting widespread nitrate pollutant to ammonia under mild conditions. Among other NRA catalysts, single-atom catalyst (SAC) has emerged as a promising candidate due to its numerous advantages such as maximum metal-atom-utilization efficiency, homogeneous and tailorable active sites, which still encounters a formidable challenge to accelerate the NRA kinetics and simultaneously suppress the competitive hydrogen evolution reaction, especially when operated in the electrolytes with low concentration nitrate. Herein, a general strategy is reported to prepare defect-enriched coordination polymer catalysts featuring with well-defined and unsaturated single-atom metal sites, which can exhibit exceptional NRA performance even at low nitrate concentration and surpass other reported SACs toward NRA catalysis. Taking cobalt (Co) as an example, defect-enriched Co-based coordination polymers (d-CoCP) and its counterpart CoCP without defects are investigated as the proof-of-concept study. Both the experimental and theoretical results elucidate that the elaborately-engineered defects in the d-CoCP can markedly decrease the thermodynamic barrier for reducing *NO to *HNO at the rate-limiting step along NRA pathway, thus accelerating the adsorption of nitrate and promoting the NRA kinetics.