Unraveling Subsurface Hydrogen Spillover Dynamics in Pt ₁ /Ag(111) Single-Atom Near-Surface Alloys

Subsurface hydrogen transport in alloys offers poison resistance and enhanced adsorption capacity compared to surface-mediated processes, yet its underlying dynamic mechanisms remain largely elusive. Herein, we employ machine learning-accelerated molecular dynamics simulations to investigate atomic-scale hydrogen spillover dynamics in Pt1/Ag single-atom near-surface alloys. We identify two distinct penetration pathways: a H–H collision-induced mechanism, where impulsive interactions between dissociated H atoms at the Pt1 site transiently enhance the vertical kinetic energy of one atom, enabling barrier overcoming and subsurface entry; and a surface spillover-mediated mechanism, involving initial hopping of hydrogen species across Ag sites coupled with stabilization from subsurface Pt atoms that collectively facilitate subsequent penetration. In addition, subsurface diffusion shows higher mobility and a stronger temperature response than surface diffusion. These findings provide fundamental insights into subsurface hydrogen transport and establish design principles for advanced catalytic and hydrogen storage systems through subsurface engineering.