Overpotentials and Faraday Efficiencies in CO sub(2) Electrocatalysis-the Impact of 1-Ethyl-3-Methylimidazolium Trifluoromethanesulfonate

The mixtures of room temperature ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM]TFO) and water as electrolytes for reduction of CO sub(2) to CO are reported. Linear sweep voltammetry shows overpotentials for CO sub(2) reduction and the competing hydrogen evolution reaction (HER), both of which vary as a function of [EMIM]TFO concentration in the range from 4 10 super(-3)m (0.006 mol%) to 4869 10 super(-3)m (50 mol%). A steady lowering of overpotentials up to an optimum for 334 10- super(3)m is identified. At 20 mol% and more of [EMIM]TFO, a significant CO sub(2) reduction plateau and inhibition of HER, which is limited by H sub(2)O diffusion, is noted. Such a plateau in CO sub(2) reduction correlates to high CO Faraday efficiencies. In case of 50 mol% [EMIM]TFO, a broad plateau spanning over a potential range of 0.58 V evolves. At the same time, the overpotential for HER is increased by 1.20 V when compared to 334 10 super(-3)m and, in turn, HER is largely inhibited. The Faraday efficiencies for CO and H sub(2) formation feature 95.6% plus or minus 6.8% and 0.5% plus or minus 0.3%, respectively, over a period of 3 h in a separator divided cell. Cathodic as well as anodic electrochemical stability of the electrolyte throughout this time period is corroborated in super(1)H NMR spectroscopic measurements. Mixtures of ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and water as electrolytes for reduction of CO sub(2) are characterized. Broad reduction plateaus spanning overpotential ranges of up to 0.58 V evolve, while the hydrogen evolution reaction is largely inhibited. Consecutively, the Faraday efficiencies for CO feature high values and the process is stable.