Summary In Chapter 3 it was found that the acidity of the C-2 protons of imidazolium cations play a key role in co-catalyzing the reduction of CO2 at the Au electrode. In this chapter we will extend the library of cations for which the acidity is modified by C4,C5-substituents. Three remarkable results will be extensively discussed. First, the 1,3,4,5-tetramethyl imidazolium (TetraMe) cation unsurprisingly exhibits a higher overpotential requirement for CO2 reduction compared to MM. This outcome finds concurrence with both the 13C carbon NMR data and the Voronoi Deformation Density (VDD) charge analysis, both indicating an escalated positive charge density linked with the C2-H2 of MM cation. Furthermore, a surprising observation emerges from the divergent behavior exhibited by the MM cation and the 1,3-dimethyl-4,5-diphenyl imidazolium (DiPh) cation in chronoamperometry measurements for CO2 reduction. Notably, while the required potential increases with the MM cation, it leads to an overall enhanced performance for the DiPh cation. The improved performance of DiPh in steady-state electrolysis experiments aligns with its higher acidity, as verified through VDD charge analysis and pKa determination. However, this result contrasts with the LSV findings, which indicate a more negative onset potential for CO2 reduction with the bulkier DiPh cation. We tentatively explain this observation by differences in hydrophobicity – the MM cation is less hydrophobic, and therefore more susceptible to interactions with residual water within the surface boundary layer – causing the time-dependent formation of adsorbed species after deprotonation, as previously proposed in the literature. These adsorbed species could potentially exert an influence on the CO2 reduction under steadystate conditions, resulting in a higher overpotential for the MM cation. The final observation is the notably lower onset potential observed for the 1,3-dimethyl-4,5-dichloro imidazolium (DiCl) cation, compared to the MM cation. This observation is consistent with the higher C2H2 positive charge density for DiCl. However, chronoamperometry measurements for the DiCl
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