influenced by the flexible and lengthy alkyl chains, may contribute to their co-catalytic effects on CO2 reduction. Considering the cationic nature of the imidazolium cations and their presence in the double layer, it is plausible that larger cations with more extensive alkyl chains exert their influence on CO2 reduction through steric effects. Aldous and Hardwick135 observed that longer-chain organic cations slow down the rate of electrode kinetics for oxygen reduction on Au electrodes in acetonitrile. They argued that cations with longer alkyl chains reduce the activity of the Au electrode due to competitive adsorption. Similarly, our findings with 1-alkyl-3-methyl cations, including MM, HM, and NM (Figure 7.1), demonstrate a decrease in activity when a longer alkyl chain is present at the N1position. This negative effect of longer alkyl chain length on the kinetics of CO2 reduction has also been observed on Ag electrodes using different tetra-alkyl ammonium cations136. In general, to optimize the performance with imidazolium cations for CO2 reduction, it is advisable to consider cations with the shortest alkyl chain lengths, to prevent steric hinderance and allow coordination of the C2 proton with adsorbed CO2. Further investigations incorporating in situ 0.134 0.091 0.134 0.091 0.135 0.095 Figure 7.1. (a) Cyclic voltammetry results obtained with 0.5 mol% of three different imidazolium cations in CO2-saturated anhydrous acetonitrile. The cations investigated include: 1,3-dimethylimidazolium NTf2 (MM), 1-methyl-3-heptyl imidazolium (HM), and 1-methyl-3-nonyl imidazolium (NM). (b) Comparison of the structures for the three investigated cations in acetonitrile, obtained through DFT calculations. Additionally, the VDD charges of the C2-H2 bonds for each cation are displayed. The B3LYP exchange correlation functional was utilized for all the calculations. b a
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