A new family of nickel-based catalysts featuring redox-active bipyridyl-N-heterocyclic carbene-based macrocycles has been developed for the electrocatalytic reduction of CO2 to CO. Electrochemical studies show that macrocyclic character plays a crucial role in the selection for performing CO2 reduction over the competing proton reduction reaction; for example, the non-macrocyclic, and therefore most flexible catalyst of the series, favors proton reduction over CO2 reduction with Faradaic efficiencies for H2 production at 93%. However, with enhanced rigidity of the macrocycle, selectivity and activity for CO2 reduction are increased, such that in the third and most rigid species the catalyst produces CO with a Faradaic efficiency of 87%. Electronic structure calculations reveal that selection for CO2 reduction or proton reduction may come down to a delicate electronic balance between metal and ligand-based redox chemistry. Unlike other Earth-abundant analogs of these systems, the nickel-based family exhibits unusual behavior in which the N-heterocyclic carbene (NHC) ligands may function as an alternative site for CO2 binding and therefore reduction. Again, stabilization of the CO2 adduct by the ligand may be understood through a subtle structure-activity relationship.

New family of highly tunable nickel-based electrocatalysts for the reduction of CO2 to CO

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.