Investigation of the Electrical Double Layer with a Graphene Electrode by the Grand Canonical Monte Carlo Simulation

Abstract

Structural and thermodynamic properties of the electric double layer with a graphene electrode are investigated by the grand canonical Monte Carlo simulations. The nonelectrostatic carbon–ion and ion–ion interactions are described by the Lennard-Jones potential. The results (the ion singlet distribution functions, the mean electrostatic potential, the integral, and the differential capacitance) for an explicit corpuscular structure are compared with those obtained for the structureless carbon sheet and hard surface electrodes. Simulations are carried out for 1.0 mol/dm3 1:1 electrolyte at T = 298.15 K and εr = 78.5 in the range of the electrode surface charge density from −0.9 to +0.9 C/m2. The surface density of carbon atoms in graphene is 5.03066 × 1019 m–2. The singlet distribution functions of ions show that the ion adsorption at the carbon electrodes is evidently stronger than that at the hard surface electrode. The profiles of the mean electrostatic potential near the positively charged carbon electrodes have a minimum that is characteristic of divalent anions near a hard surface electrode. For both carbon electrodes, the integral and differential capacitance curves have the bell shape with a broad maximum, while the curve for the hard surface electrode has a camel-like shape with two humps. The difference between the graphene and structureless carbon electrodes is manifested mainly in capacitance. In the range of a small magnitude of electrode charges, the capacitance results for the graphene electrode are smaller than those for the structureless carbon electrode.