Hydrated Proton Structure and Diffusion at Platinum Surfaces

Abstract

Water-mediated hydrated proton solvation and diffusion at two types of platinum−water interfacesnamely, the Pt(111) and the Pt(100) surfacesis investigated using reactive molecular dynamics simulations. The adsorbed water molecules on these platinum surfaces create different hydrogen-bonding networks, resulting in different proton solvation and transport behavior. Free energy calculations show that the excess proton can be stably adsorbed on the Pt(111) surface, while on the Pt(100) surface it prefers to stay at the interface between the hydrophobic layer of adsorbed water and the bulk. The hydrated excess proton can be viewed as a charge defect in the adsorbed water layer, where it diffuses with a low rate due to the slow reorientational dynamics of the adsorbed water molecules. However, the proton can sample a larger surface area by hopping between the adsorbed layer and the bulk at the Pt(111) surface.

Photophysics and electrochemistry relevant to photocatalytic water splitting involved at solid–electrolyte interfaces

“…Conversely, the same simulations indicated that the hydronium ion cannot be embedded within the water layer adsorbed on the Pt (100) surface [83] . The reason for this different behavior is in the capability of hydronium ions to form hydrogen bonds without interrupting the large-scale HBN in the water layer adsorbed on the Pt (111) surface.…”

“…This can be analogue to the prototypical problem of "ions at water-hydrophobic interfaces". It is not surprising that the small hydronium ion can stay between the hydrophobic adsorbed water layer and the other water molecules above it [83] . Further, the hydronium ion can be embedded within the water layer adsorbed on the Pt (111) surface and form a relatively stable structure by forming three hydrogen bonds with the surrounding water molecules [83] .…”

“…It is not surprising that the small hydronium ion can stay between the hydrophobic adsorbed water layer and the other water molecules above it [83] . Further, the hydronium ion can be embedded within the water layer adsorbed on the Pt (111) surface and form a relatively stable structure by forming three hydrogen bonds with the surrounding water molecules [83] . The stable hydrogen-bonding network (HBN) formed with the adsorbed water layer can affect the hydronium ion translocation: within the adsorbed water layer, the hydronium ion is limited within the defect of the HBN; if a proton can be transferred between the adsorbed water layer and the other water molecules above it, the hydronium ion can visit a much larger area.…”

Recent advances in quantum‐mechanical molecular dynamics simulations of proton transfer mechanism in various water‐based environments

“…Among the RFF approaches, the most popular method for revealing mechanistic details and elucidating structural and dynamical properties of the PT process is the multiple empirical valence bond (MS‐EVB) . The application of MS‐EVB to examine proton dynamics has been investigated in diverse model systems ranging from H 3 O + and OH − diffusion in bulk water, water–ice interface, and confined water environment to metal surfaces . The deliberate fitting of empirical parameters for achieving improved accuracy may be a lengthy task before starting MD simulations, thereby limiting the applicability of MS‐EVB over a broad range of systems.…”

“…[25][26][27] The application of MS-EVB to examine proton dynamics has been investigated in diverse model systems ranging from H 3 O + 28-45 and OH − 41,46 diffusion in bulk water, water-ice interface, 47 and confined water environment [48][49][50] to metal surfaces. 51,52 The deliberate fitting of empirical parameters for achieving improved accuracy may be a lengthy task before starting MD simulations, thereby limiting the applicability of MS-EVB over a broad range of systems.…”