Accessing and Photo-Accelerating Low-Overpotential Pathways for CO₂ Reduction: A Bis-Carbene Ruthenium Terpyridine Catalyst
A ruthenium catalyst bearing a bidentate bis(carbene) ligand is prepared and studied as a catalyst for CO₂ electroreduction. The catalyst [Ru(tpy)(bis-mim)(MeCN)][PF₆]₂ (tpy) is 2,2′,:6′,2″-terpyridine; bis-mim is (methylenebis(N-methylimidazol-2-ylidene)) mediates reduction of CO₂ into CO with a turnover frequency of 630 s⁻¹ and Faradaic efficiency (FE) of 30% at an overpotential of 730 mV. The strongly donating bis(carbene) ligand also enables access to a pathway operating at a lower overpotential of ca. 310 mV. While low-overpotential catalysis is slow in the dark (TOF = 0.01 s⁻¹), visible light illumination increases the rate 10-fold (TOF = 0.11 s⁻¹). A full mechanistic picture is developed using kinetic analysis from cyclic voltammetry, spectroelectrochemistry, and computational methods, with the bis-mim ligand facilitating rapid CO₂ activation at low overpotentials. Comparisons with other ruthenium catalysts yield insight into the ability to tune the rate of chemical steps (e.g., ligand dissociation and CO₂ nucleophilic attack) and the overpotential by tailoring the primary coordination sphere while retaining the “redox-active” tpy ligand.
Assaf, E. A.; Gonell, S.; Chen, C-H.; Miller, A. J. M. “Accessing and Photo-Accelerating Low-Overpotential Pathways for CO₂ Reduction: A Bis-Carbene Ruthenium Terpyridine Catalyst” ACS Catal. 2022, 12 (20) 12596–12606. https://doi.org/10.1021/acscatal.2c03651
