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

## TL;DR

This paper employs molecular density functional theory to study water-graphene interfaces, revealing structural and dielectric changes under voltage, and validating the approach against molecular dynamics results.

## Contribution

It advances the field by incorporating realistic atomic resolution electrodes and a molecular water model in DFT calculations at fixed potentials.

## Key findings

- Water structure at the interface changes with voltage.
- Water dielectric permittivity varies under applied voltage.
- Capacitance results agree with molecular dynamics simulations.

## 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.