the reference spectra, the formation of BMMIM carbonation and BMMIM bicarbonate are evident. However, NMR results from the white precipitate only indicate the formation of bicarbonate and formate species. This suggests that carbonate species are likely to remain soluble in acetonitrile and will play a role in oxidation reaction. The formation of bicarbonate and formate requires the presence of protons. As we did not observe water reduction over Au film, these species can only be formed by interactions with protons resulting from water oxidation over the counter electrode or due to residual water present along with the electrolyte at the cathode electrode. An intermediate proposed for formation of CO and (bi)carbonate is the *C2O4 - (MetalC(=O)COO-) – known as the CO2 dimer radical anion. This intermediate, upon a second electron transfer accompanied by bond cleavage, leads to the formation of CO and carbonate anions, the latter following protonation to form bicarbonate. This mechanism has been proposed for CO2 reduction at CdS and ZnS nanocrystals, where CO2 serves as an oxygen acceptor 132-133. Sheng et al.132 demonstrated that the presence of such an intermediate would result in the appearance of three bands within the 1000-1700 cm-1 region, exhibiting a 13C shift exceeding 30 cm-1. However, in our case, we do not observe any new peaks displaying significant 13C shifts, apart from those assigned to carbonate (Figure 6.3). Consequently, the lifetime of this intermediate is apparently that short, that we do not observe this spectroscopically. To observe such intermediate, rapid scan measurements are required (allowing ms time resolution), or even step-scan experiments (allowing microsecond time resolution). Formation of Oxalate In addition to the formation of CO and bicarbonate, another significant product of CO2 reduction previously reported is the creation of oxalate. Our experiment also reveals the presence of this compound, which accounts for the appearance of a band around ~1732 cm-1 in
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