Fuel cells based on methanol oxidation are sustainable alternatives to burning fossil fuels; however, electrocatalysts for these reactions utilize expensive noble metals which inhibits their broader adoption. A first step in designing less expensive electrocatalysts is to understand how current materials function. This has proven challenging, however, due to complexities involved with the liquid reaction conditions and how they are influenced by an external field. Understanding the role of liquid water in an external field is hence critical to electrocatalyst design. Herein, we use a combination of classical molecular dynamics (cMD) and density functional theory (DFT) to illustrate how explicit liquid water in an external electric field influences the solvation thermodynamics of intermediates in the pathway for methanol oxidation. Using this multiscale approach, we compute energies and entropies of solvation of CH<sub>3</sub>OH, COH, and CO adsorbates. We find that both the energies and entropies of solvation are influenced by the external field. Entropies of solvation are particularly influenced, due to the field influence on the structure of interfacial water. Specifically, in the absence of an external field, the structure of interfacial water is dictated by the catalytic species, whereas in the presence of an external field, the structure of water is defined by the field itself. We show that competition between adsorbates and the field on the structure of water at the interface can lead to large entropic effects which have significant impact on the free energies of interfacial species.

Influence of an electrified interface on the entropy and energy of solvation of methanol oxidation intermediates on platinum(111) under explicit solvation

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ACS Fall 2022

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