The planar electric double layer capacitance for the solvent primitive model electrolyte.

The planar electric double layer capacitance of the solvent primitive model electrolyte is studied using simulation and two versions of the modified Poisson-Boltzmann theory. At small values of the surface charge and varying electrolyte concentration, the capacitance has a behaviour analogous to that of the restricted primitive model electrolyte. As the electrolyte concentration is increased at a fixed total packing fraction, the minimum at zero surface charge changes to a maximum. This qualitative change is predicted by both simulation and the modified Poisson-Boltzmann theories. The transition envelope, separating the change in the capacitance from a minimum to a maximum at zero surface charge, is shifted from the restricted primitive model value to higher ion densities at fixed total packing fractions.