Dipolar depletion effect on the differential capacitance of carbon-based materials
1 Department of Applied Physics and COMP center of Excellence, Aalto University School of Science P.O. Box 11000, FI-00076 Aalto, Espoo, Finland, EU
2 Department of Physics, Brown University - Providence, Box 1843, RI 02912-1843, USA
Received: 10 March 2012
Accepted: 29 May 2012
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.
PACS: 03.50.De – Classical electromagnetism, Maxwell equations / 05.70.Np – Interface and surface thermodynamics / 77.55.Bh – Low-permittivity dielectric films
© EPLA, 2012