The carbonate related feature around 3400 cm -1 also becomes more prominent in CO 2purged NaCl electrolyte at catalytic potentials compare to Ar-purged NaCl electrolyte as shown in Figure . Figure shows the potential dependent water spectra of Ar-purged 0.1 M NaCl electrolyte. Even at -1 V, the peak intensity around 3400 cm -1 is quite small; however, when the electrolyte was saturated with CO 2 , the peak intensity increased significantly. In CO 2 -purged NaCl electrolyte, once the onset of catalytic Faradaic curret is reached, the interfacial pH may increase, and CO 3 2-anions are generated at the surface resulting in the appearance of the characteristic 3400 cm -1 feature. This suggests that the interfacial species responsible for this features are likely ubiquitious at electrode-electrolyte interfaces during CO 2 R electrocatalysis.