Abstract
The liquid water-Pt(111) interface is studied with constant temperature ab initio molecular dynamics to explore the importance of liquid water dynamics of catalytic reactions such as the oxygen reduction reaction in PEM fuel cells. The structure and energetics of hydroxyls formed at the liquid water-Pt(111) interface are found to be significantly different from those of the hydroxyl formed on a bare Pt(111) surface and the hydroxyl formed on a Pt(111) surface with a static water layer. We identify 1/12 ML *OH, 5/12 ML *OH and 2/3 ML *OH as particularly stable hydroxyl coverages in highly dynamic liquid water environments, which - contrary to static water-hydroxyl models - contain adjacent uncovered Pt sites. Atomic surface oxygen is found to be unstable in the presence of liquid water, in contrast to static atomic level simulations. These results give an improved understanding of hydroxide and surface oxide formation from Pt(111) cyclic voltammetry and allow us to draw detailed connections between the electrostatic potential and the interface structure. The study of hydrogen adsorption at the liquid water-Pt(111) interface finds competitive adsorption between the adsorbed hydrogen atoms and water molecules. This does not adhere with experimental observations, and this indicates that the Pt(111) surface has to be negatively charged for a correct description of the liquid water-Pt(111) interface at potentials where hydrogen adsorption occurs.
Highlights
Electro-catalysis with aqueous electrolytes has been studied extensively by computational modeling at the atomic level and signi cant insight has been gained
We find that specific *OH surface coverages are stable, namely ~0.08, 0.42 and 0.67 ML, which agrees with the butterfly feature seen in Pt(111) cyclic voltammetry
The observation of low surface coverage and larger second layer coverage is in agreement with other Ab initio molecular dynamics (AIMD) simulations of water on Pt(111),[20,22] but different from certain molecular dynamics (MD) simulations based on inter-atomic potentials, which predict close to 1 ML coverage of surface bound water molecules.[40]
Summary
Electro-catalysis with aqueous electrolytes has been studied extensively by computational modeling at the atomic level and signi cant insight has been gained. This does not adhere with experimental observations, and this indicates that the Pt(111) surface has to be negatively charged for a correct description of the liquid water–Pt(111) interface at potentials where hydrogen adsorption occurs.
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