Local order of liquid water at the electrochemical interface

TL;DR

This study uses ab initio molecular dynamics to compare the structure and dynamics of liquid water at Pd and Au (111) surfaces, revealing distinct interfacial arrangements influenced by dispersion forces and charge transfer effects.

Contribution

It provides new insights into the atomic-scale structure of water at metal interfaces, highlighting the importance of van der Waals interactions and charge transfer, which are often neglected in simpler models.

Findings

Water forms two domains at Pd with opposite dipoles

Au interface exhibits a single domain with no in-plane order

Dispersion forces significantly affect interfacial water structure

Abstract

We study the structure and dynamics of liquid water in contact with Pd and Au (111) surfaces using \emph{ab initio} molecular dynamics simulations with and without van der Waals interactions. Our results show that the structure of water at the interface of these two metals is very different. For Pd, we observe the formation of two different domains of preferred orientations, with opposite net interfacial dipoles. One of these two domains has a large degree of in-plane hexagonal order. For Au a single domain exists with no in-plane order. For both metals, the structure of liquid water at the interface is strongly dependent on the use of dispersion forces. The origin of the structural domains observed in Pd is associated to the interplay between water/water and water/metal interactions. This effect is strongly dependent on the charge transfer that occurs at the interface, and which is not modeled by current state of the art semi-empirical force fields.