VIII. Notes on the initial act of the electrode As argued in the article a first electron transfer to the imidazolium cation violates the role of the heterogeneous catalyst and the electrode turns into an electron supplier with some affinity for a given cation. That is similar to what has been proposed for the pyridinium chemistry at electrodes such as Pt81-82. For CO2 reduction with pyridinium as a molecular electro-catalyst, the cation first reduces to form a radical active form, and with the followup electron-proton transfers, CO2 is reduced to products such as methanol and formic acid. The CV profile for such a system shows the same onset potential for the reduction of the cation and the reduction of CO2 (Figure S3.14 a). This implies that the first electron transfer to pyridinium is involved in the initial stages of the mechanism. However, with imidazolium, there is a significant difference between the onset potential for the reduction of the cation and the onset potential for the reduction of CO2 (Figure S3.14 b). Even with seven times higher concentrations of MM compared to CO2, we did not observe cation reduction in the potential region in which CO2 reduction occurs. This observation challenges the idea of the first electron transfer to imidazolium as an initial step, otherwise, similar to pyridinium chemistry we would observe the same onset potentials for the reduction of the cation and the reduction of CO2. Indeed, a proposed mechanism for imidazolium-assisted electrochemical CO2 reduction should consider the role of the electrode catalyst in adsorbing CO2 and facilitating electron transfer to adsorbed CO2.
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