ACS Catalysis | 2019
Robust and SelectiveCobalt Catalysts Bearing Redox-ActiveBipyridyl‑ N ‑heterocyclic Carbene Frameworksfor Electrochemical CO 2 Reduction in Aqueous Solutions
Abstract
An original series of cobalt complexes bearing redox-active ligands based on bipyridyl-N-heterocyclic carbene donors has been developed for electrocatalytic CO2 reduction in acetonitrile and aqueous solutions. The mechanism was examined by electrochemical methods and electronic structure calculations. From controlled potential electrolysis (CPE) in CH3CN/2% H2O solutions, 1-Co supported by a non-macrocyclic ligand gives a Faradaic efficiency (FE) for CO2-to-CO conversion of 78%, while 2-Co and 3-Co supported by tunable macrocycles afford higher selectivities for CO evolution with FEs of 91% and 98%, respectively, with the balance of charge going to H2 production in each case. Electrochemical experiments show that the turnover frequencies across the catalyst series increase systematically from 66 s–1 (1-Co) to 570 s–1 (3-Co). These results demonstrate that increasing the rigidity of the ligand framework enhances catalytic activity and selectivity for CO2 reduction over the competing H2 evolution reaction. ...