Study of a water-graphene capacitor with molecular density functional theory

Abstract

Most of the performances of electrochemical devices are governed by molecular processes taking place at the solution-electrode interfaces and molecular simulation are the main way to study these processes. Aqueous electrochemical systems have often been studied using classical DFT but with too crude approximations to consider the system description to be realistic. We study the interface between graphene electrodes and liquid water at different applied voltage using molecular DFT, improving the state of the art by the following key points: 1) electrodes have a realistic atomic resolution, 2) classical DFT calculations are carried out at fixed imposed potential difference and 3) water is described by a molecular model. This allows to reveal the structural modification of water adsorbed at the graphene interface and the evolution of water dielectric permittivity when a voltage is applied. The computed capacitance of this device is in agreement with molecular dynamics simulations. This demonstrates the relevance of molecular DFT to study electrochemical systems at the molecular level.

6 pages, 5 figures, Supplementary infos

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• The electric double layer has a life of its own
• Molecular Density Functional Theory of Water
• Scalar fundamental measure theory for hard spheres in three dimensions. Application to hydrophobic solvation
• Efficient molecular density functional theory using generalized spherical harmonics expansions
• Molecular Density Functional Theory for water with liquid-gas coexistence and correct pressure
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• Multi-scale simulation of the adsorption of lithium ion on graphite surface: from Quantum Monte Carlo to Molecular Density Functional Theory
• Mesoscopic simulations of the in situ NMR spectra of porous carbon based supercapacitors: Electronic structure and adsorbent reorganisation effects
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• Brownian dynamics simulations of electric double-layer capacitors with tunable metallicity
• Tackling solvent effect by coupling electronic and molecular Density Functional Theory