  The mesoscopic field theory for ionic systems [A. Ciach and G. Stell, J. Mol.
Liq. 87, 255 (2000)] is extended to the system with charged boundaries. A very
simple expression for the excess grand potential functional of the charge
density is developed. The size of hard-cores of ions is taken into account in
the expression for the internal energy. The functional is suitable for a
description of a distribution of ions in ionic liquids and ionic liquid
mixtures with neutral components near a weakly charged wall. The Euler-Lagrange
equation is obtained, and solved for a flat confining surface. An exponentially
damped oscillatory charge density profile is obtained. The electrostatic
potential for the restricted primitive model agrees with the simulation results
on a semiquantitative level.
