Performance of Transition Metals in Imidazolium-Assisted CO₂ Reduction in Acetonitrile

This study explores the electrochemical reduction of CO₂ in dry acetonitrile containing 1,3-dimethyl imidazolium cations, utilizing late-transition metals (Au, Ag, Zn, Cu, and Ni). All metals exhibit remarkable selectivity, nearing 100 %, for CO formation. Particularly noteworthy is Au, which manifests the lowest (−2.37 V vs. Ag/Ag⁺) overpotential in chronopotentiometry experiments. We propose that, for metals with lower CO binding energies compared to Au (Ag and Zn electrodes) – calculated by DFT, the rate-determining step is the adsorption of CO₂. This distinction in CO₂ adsorption is reinforced by the examination of partial charge transfer from negatively charged slabs to CO₂ (−0.241 a.u with the Au electrode and +0.002 a.u with the Zn electrode). Conversely, the greater CO binding energy calculated for Cu and Ni likely diminishes electrocatalytic activity relative to the Au electrode. Our results unveil a volcano trend in catalyst activity, albeit with smaller performance disparities between the late-transition metals and Au than previously observed in aqueous conditions, possibly due to the co-catalytic influence of imidazolium cations. This study suggests that metals unsuitable for aqueous environments hold promise for cost-effective and viable electrochemical conversion of CO₂ to CO in non-aqueous media containing imidazolium compounds.