As ions approach an electrode interface, both the free energy to dissociate an ion pair and the magnitude of the auxiliary ion effects on dissociation free energy increase. The increased free energy cost of ion dissociation can be partially attributed to the volume excluded by the electrode interface. In bulk water, when Na + is a distance r away from CO , it can isotropically access every point in a sphere of that radius. When carbonate approaches an interface, part of this sphere would fall within the electrode, which excludes Na + from these regions. As a result, the set of configurations consistent with a Na-C distance is truncated by the electrode, leading to a net destabilization of the dissociated state.