Figure 2.10a depicts the experimental results for three catalysts (Ni, Ag and Zn) where 0.1 mol% (0.02 molar) of Ag OTf was added to the reference capillary, with an Ag wire serving as the reference electrode. The corresponding electrodes are labeled as Ag 500, Ni 500, and Zn 500. In contrast, Figure 2.10b shows the results obtained when the electrolysis experiments were conducted according to the protocol devised in this study. Interestingly, there are no noticeable differences in the activity of Ni, Zn, and Ag catalysts for CO2 reduction when Ag OTf is consistently used as the reference solution (Ni 500, Ag 500, and Zn 500). However, when the reference solution is removed from the capillary and our protocol is applied to perform electrolysis, the differences between the three catalysts become evident. We also note that all three electrodes display more negative overpotentials for the same current density as compared to Ag 500, Ni 500 and Zn 500. After conducting EDX-SEM analysis on the electrode surfaces following electrolysis (Supporting Information Figure S2.2), it was observed that Ag, carbon, and oxygen were present. This finding is reminiscent of the situation observed for the Pt electrode, as shown in Figure 2.5. It is important to note that the concentration of Ag in the reactor was 20 ppm at maximum, indicating that the deposition of Ag alone cannot account for the improved overpotentials observed for Ni 500, Ag 500, and Zn 500 electrodes compared to the situation when Ag OTf was not used. Therefore, we can conclude that the similar catalytic performance observed for Ni 500, Ag 500, and Zn 500 can be attributed to a modified catalytic behavior associated with Ag-MM deposition during the electrolysis process. While EDX-SEM analysis for electrodes used in Figure 2.9b did not show any evidence of Ag deposition, carbon, nitrogen, and oxygen species were still present for all three catalysts (Supporting Information Figure S2.3). This observation implies the potential deposition of carbonyl and MM cation during electrolysis. Our experiment with the Zn electrode for 100 hours of electrolysis (Figure S2.3c) showed a very slight shift in the overpotential that could always be compensated by the gradual addition of MM cation. In line with the EDX-SEM
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