Electroreduction of CO(2) in a Non-aqueous Electrolyte—The Generic Role of Acetonitrile

[Image: see text] Transition metal carbides, especially Mo(2)C, are praised to be efficient electrocatalysts to reduce CO(2) to valuable hydrocarbons. However, on Mo(2)C in an aqueous electrolyte, exclusively the competing hydrogen evolution reaction takes place, and this discrepancy to theory was traced back to the formation of a thin oxide layer at the electrode surface. Here, we study the CO(2) reduction activity at Mo(2)C in a non-aqueous electrolyte to avoid such passivation and to determine products and the CO(2) reduction reaction pathway. We find a tendency of CO(2) to reduce to carbon monoxide. This process is inevitably coupled with the decomposition of acetonitrile to a 3-aminocrotonitrile anion. Furthermore, a unique behavior of the non-aqueous acetonitrile electrolyte is found, where the electrolyte, instead of the electrocatalyst, governs the catalytic selectivity of the CO(2) reduction. This is evidenced by in situ electrochemical infrared spectroscopy on different electrocatalysts as well as by density functional theory calculations.