Results and discussion Figure 3.1 a shows linear sweep voltammetry (LSV) for the Au disk electrode immersed in such anhydrous acetonitrile containing 0.5 mol% of 1,3-dimethyl imidazolium NTf2 (MM NTf2) introducing a purge of He or CO2 in a small conventional, undivided electrochemical cell. The absence of a noticeable faradaic current within the potential window of -1.8 to -2.2 V vs. Ag/Ag+ in the absence of CO2, demonstrates the stability of the imidazolium cation against electrochemical conversion, which is also confirmed by NMR analysis. In the presence of CO2, significant current can be observed, assigned to the conversion of CO2 to CO. Such currents are not observed when other types of cations (Cesium NTf2 and tetraethylammonium NTf2) are dissolved in acetonitrile (Figure 3.1 b). Thus, the unique ability of imidazolium cations in promoting the reduction of CO2 in anhydrous media is demonstrated. Performing the experiment in a rotating disc electrode configuration (Figures 3.1 c and 3.1 d), minimizing mass transfer limitations, demonstrates that the onset potential for CO2 activation in anhydrous MM-acetonitrile electrolyte is around -0.8 V vs. Ag/Ag+ (~ -0.258 V vs. SHE (± 45 mV), see also experimental details in Chapter 2). To the best of our knowledge, this onset potential is the lowest ever reported for activation of CO2 in non-aqueous electrolytes. Chronopotentiometry at -10 mA/cm2 shows high stability in the performance for the production of CO in the MM-acetonitrile electrolyte with 100% Faradaic efficiency (FE) (Figure 3.1 e, for the procedure used to evaluate Faradaic efficiencies see experimental protocols in Chapter 2). NMR analyses confirm that after electrolysis, MM NTf2 and acetonitrile remain unchanged (see Figures S3.31 to S3.33). It should be mentioned that the products formed in the presence of other cations such as tetrabutylammonium NTf2 are mainly hydrogen and methane (Figure S3.1), showing that not only activity (on-set potential) but also selectivity (FE) is favorably tuned by the imidazolium cation. Upon switching the CO2 flow to He, the concentration of CO decreases gradually while the cell potential increases. Using 10 mL of the MM-acetonitrile
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