Many reports indicate that the identity of the hydrated cation at the charged interface determines its catalytic activity, although the mechanism behind specific ion effects on CO 2 R remains an open question. Early explanations explored the structure of the double layer and the corresponding potential drop across the interface, while more recent studies have shown that interfacial solvation structure can mediate reactions, arguing for explicit treatment of solvation in kinetic models of CO 2 R. While it is known that the presence of cations at the charged interface is integral for CO 2 R activity, the mechanism behind cation-dependent efficiency trends are still widely debated. Possible molecular reasons for the relation between cation identity and efficiency include cationdependent pKa of hydrolysis, cation-specific electric field effects, and the effect of specific cations on the solvation-induced Onsager reaction field present at the interface during CO 2 R. All of these theories point to the need for a molecular understanding of ion interactions at electrified surfaces and the effect of discrete ions and ion pairs on the alignment and hydrogen-bonding structure of interfacial water.