The computational hydrogen evolution activity of Pt(111) remains controversial due to apparent discrepancies with experiments concerning rate-determining activation free energies and equilibrium hydrogen coverages. A fundamental source of error may lie in the static representations of the metal–water interface commonly employed in density functional theory (DFT)-based models neglecting important entropic effects on reaction dynamics. Here, I present a dynamic study of the Volmer–Tafel hydrogen evolution pathway on Pt(111) through DFT-based constrained molecular dynamics simulations and thermodynamic integration [1]. Hydrogen coverage effects are studied at two surface saturations, while the critical potential dependence and constant potential conditions are accounted for using a capacitive model of the electrified interface. The dynamic description of the electrochemical interface promotes a substantial decrease in the Tafel free energy barrier as the coverage is increased to a full monolayer. This follows from a decreased entropic barrier due to suppressed adlayer dynamics compared to the unsaturated surface, a detail easily missed by static calculations predicting notably higher barriers at the same coverage. I will also discuss another work focusing on the difference between the static (NEB) and AIMD simulations of the same reactions [2].
[1] Kronberg and Laasonen, ACS Catal. 2021, 11, 13, 8062–8078
[2] Kronberg, Lappalainen, Laasonen. Phys. Chem. Chem. Phys. 2020, 22, 10536– 10549
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