Dipolar depletion effect on the differential capacitance of carbon based materials

TL;DR

This paper explains the low capacitance of carbon-based materials in water by introducing a microscopic dipolar model that accounts for solvent depletion effects at the interface, matching experimental data without fitting parameters.

Contribution

It develops a non-mean-field dipolar Poisson-Boltzmann equation to incorporate solvent depletion effects due to dielectric discontinuity, providing a microscopic explanation for capacitance behavior.

Findings

Good agreement with experimental capacitance data

No fitting parameters needed for the model

Highlights importance of solvent depletion effects

Abstract

The remarkably low experimental values of the capacitance data of carbon based materials in contact with water solvent needs to be explained from a microscopic theory in order to optimize the efficiency of these materials. We show that this experimental result can be explained by the dielectric screening deficiency of the electrostatic potential, which in turn results from the interfacial solvent depletion effect driven by image dipole interactions. We show this by deriving from the microscopic system Hamiltonian a non-mean-field dipolar Poisson-Boltzmann equation. This can account for the interaction of solvent molecules with their electrostatic image resulting from the dielectric discontinuity between the solvent medium and the substrate. The predictions of the extended dipolar Poisson-Boltzmann equation for the differential capacitance are compared with experimental data and good agreement is found without any fitting parameters.