Figure 4.7 displays the outcomes of electrolysis experiments involving MM and DiPh cations. The data reveals two distinct patterns. In the initial 1000 seconds, the MM cation displays a lower overpotential, aligning with the findings from the LSV results. However, after this, the MM cation experiences a gradual rise in the needed overpotential before attaining a stable performance. In contrast, the phenyl-substituted cation demonstrates a decrease in overpotential over time. Notably, a crossover of the required potential for both cations becomes evident after approximately 1000 seconds of experimentation. Overall, the phenyl-substituted cation achieves the best performance, notably by lowering the necessary potential by around 250 mV. Phenyl substituents are indeed hydrophobic functionalities, and it is reasonable to expect that these substituents would hinder the association of water molecules with the cation residing in the double layer. Bi et al.92 have demonstrated that hydrophobic ionic liquids can help keep water molecules away from negatively charged electrodes in humid conditions. Therefore, in the case of the DiPh cation, we can anticipate an effect from the reduced presence of residual water in the electric double layer (EDL) compared to cations such as MM. In our experiments, there is inevitably some residual water present in the electrolyte, typically up to 50 ppm, which is challenging to eliminate in an experimental setup open to the atmosphere. Considering the Figure 4.7. Electrolysis at -1 mA/cm2 with 0.5 mol% MM-NTf2 (red) and DiPh-NTf2 (olive) for CO2 reduction in anhydrous acetonitrile. The dashed line indicated the time after which steady state is reached.
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