The NaCl-to-water ratio in each system was fixed at approximately 1:55, which corresponds to a 1 M solution in a bulk electrolyte. Each graphene sheet has dimensions of approximately 45 Å by 45 Å, with the precise value adjusted to accommodate the target ionto-water ratio as closely as possible. The equilibrium height of the slit and thus the density of the solution was determined via additional simulations in which one of the graphene sheets was allowed to move in the z-direction (perpendicular to the sheet) under the force of a piston applying 1 atm of pressure. Using this method, we prepared five slits that contained 1-5 layers of water; see the density profiles in Fig. . Table provides the precise dimensions and number of molecules in each system. Note that while the graphene is allowed to move vertically during these piston simulations, we hold the position of all carbons fixed during our production simulations.