Electrochemical CO 2 reduction (CO 2 R) offers the promise of converting CO 2 into renewable fuels or value-added chemical feed stocks. However, controlling the efficiency and selectivity of CO 2 R remains a significant challenge. While much effort has been devoted to catalyst design, it is also widely reported that the electrolyte composition has a significant effect on reaction kinetics. In electrocatalytic processes, the electrode and the electrolyte represent the two sides of the solid-liquid interface, which forms the local environment for the electron and proton transfer reactions that drive catalysis. The interplay of these two materials, creates a unique interfacial environment where electrode polarization can modulate local electrolyte composition, ion pairing, and the resulting interfacial solvation structure, in turn influencing the electrochemical kinetics that control the viability of critical processes such as CO 2 conversion. Here we use vibrational spectroscopy and molecular simulation to study the electrode-electrolyte interface under conditions relevant to CO 2 R. We reveal how ions like Na and CO 3 , that are prevalent in CO 2 systems, can form correlated ion complexes that modulate electric fields at the interface through their polarization of the surrounding water.