We observe that the ion-water diffusion length increases as the degree of confinement increases. This shift toward a more vehicular diffusion mechanism is particularly pronounced in the two most confined systems, which is consistent with the decreases in L ++ self and L -- self observed in these slits. Such a trend is likely due to the increased steric constraints on solvation imposed by the graphene walls, which raise the barrier for water molecules to leave the ion's solvation shell. Indeed, in the most confined system we see higher free energy barriers for a water molecule to transition from the first to the second solvation shell of an ion (see the ion-water potentials of mean force in Fig. ). Together with the densitydriven changes to diffusion, this changing diffusion mechanism gives rise to the observed Nernst-Einstein transport trends observed in Fig. .