How to simulate EDLC (Electrochemical Double Layer)?

GROMACS version: 2023.2
GROMACS modification: No

Dear All,
I tried to simulate a electrode (Zn 002 Plane) electrolyte (Zinc Sulfate) system under applied potential condition.
To some extent I have performed the simulation.
Work so far done:

  1. Created electrolyte simulation box and done equilibriation and nvt simulation (Output: I got constant density of system)
  2. Now I placed this system between Zn 002 plane (4-layer each). A small amount of charge is added on top layer of Zn 002 both side to replicate electrode potential (Popularly known as constant charge method for electrode simulation).
  3. This system is allowed for NPT simulation (pbc in xy direction).

Structure I got:

Now my questions are:

  1. How to know the potential at each electrode?
  2. Why there is a gap in electrolyte near one electrode?