Highly Efficient Electrocatalytic Reduction of CO₂ to CO by a Molecular Chromium Complex

Earth-abundant transition-metal catalysts capable of reducing CO2 to useful products have been gaining attention to meet increasing energy demands and address concerns of rising CO2 emissions. Group 6 molecular compounds remain underexplored in this context relative to other transition metals. Here, we present a molecular chromium complex with a 2,2′-bipyridine-based ligand capable of selectively transforming CO2 into CO with phenol as a sacrificial proton donor at turnover frequencies of 5.7 ± 0.1 s–1 with a high Faradaic efficiency (96 ± 8%) and a low overpotential (110 mV). To achieve the reported catalytic activity, the parent Cr­(III) species is reduced by two electron equivalents, suggesting an approximate d5 active species configuration. Although previous results have suggested that low-valent species from the Cr/Mo/W triad are nonprivileged for CO2 reduction in synthetic molecular systems, the results presented here suggest that reactivity analogous to late transition metals is possible with early transition metals.