Interplay of water film dewetting and hydrogen evolution on Pt(111): Insights from a machine-generated interatomic potential

The processes that determine the kinetics of hydrogen evolution reaction (HER) on metal surfaces remain a topic of discussion despite their long-standing importance in improving the efficiency of hydrogen generation. A major cause of this uncertainty is the extreme heterogeneity of the environment at the water-metal interface, which complicates the construction of simple models. To make progress, computationally efficient modeling methods need to be developed to handle the intricate nature of the water interface. In this paper, we use an implicit electrolyte approach suitable for ab initio dynamics, which allows the surface chemistry to be explicitly modeled with density functional theory while approximating the electrolyte with a continuum method. This approach incorporates ionic screening in the electrolyte via a Poisson-Boltzmann model, enabling the modeling of charged electrochemical interfaces in a dynamic, fluctuating environment. Our results qualitatively reveal a new factor that is likely important in understanding the HER: the location and structure of the interface where hydrogen is generated differ from where protons are exchanged between the water and metal. In particular, hydrogen is generated in regions where the water density is low (i.e., where the water film has dewetted from the substrate), while the adatom-water exchange reaction occurs in regions of high water density. Thus, the diffusion of hydrogen between these regions needs to be considered in the overall kinetics and may be a rate-limiting step.