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.