Room temperature structure and energetics of water-hydroxyl layers on Pt(111)

TL;DR

This study uses neural network potentials to analyze water-hydroxyl layers on Pt(111) at room temperature, revealing new insights into their structure and energetics relevant to fuel cell catalysis.

Contribution

It introduces a neural network-based molecular dynamics approach to study water-hydroxyl interactions on Pt(111), providing detailed energetics and structural insights at room temperature.

Findings

Hydroxyl formation shows a near-linear adsorption energy profile.

The water-hydroxyl/Pt(111) interface is hydrophobic at high hydroxyl coverage.

Hydrogen bonding reduction explains increased differential adsorption energy.

Abstract

The interactions between water and hydroxyl species on Pt(111) surfaces have been intensely investigated due to their importance to fuel cell electrocatalysis. Here we present a room temperature molecular dynamics study of their structure and energetics using an ensemble of neural network potentials, which allow us to obtain unprecedented statistical sampling. We first study the energetics of hydroxyl formation, where we find a near-linear adsorption energy profile, which exhibits a soft and gradual increase in the differential adsorption energy at high hydroxyl coverages. This is strikingly different from the predictions of the conventional bilayer model, which displays a kink at 1/3ML OH coverage indicating a sizeable jump in differential adsorption energy, but within the statistical uncertainty of previously reported ab initio molecular dynamics studies. We then analyze the structure of the interface, where we provide evidence for the water-OH/Pt(111) interface being hydrophobic at high hydroxyl coverages. We furthermore explain the observed adsorption energetics by analyzing the hydrogen bonding in the water-hydroxyl adlayers, where we argue that the increase in differential adsorption energy at high OH coverage can be explained by a reduction in the number of hydrogen bonds from the adsorbed water molecules to the hydroxyls.