Dynamics of Initial Hydrogen Spillover from a Single Atom Platinum Active Site to the Cu(111) Host Surface: The Impact of Substrate Electron–Hole Pairs

Abstract

The initial impulsive diffusion of hot hydrogen atoms resulted from the dissociative chemisorption of H 2 at atomically dispersed Pt atoms embedded in Cu( 111) is investigated using ab initio molecular dynamics. Upon dissociation, one of the two hydrogen atoms tends to roam away from the dissociation site while the other remains trapped. It is shown that the fraction of diffusion and the average diffusion length increase with the incident energy and H 2 vibrational excitation, due apparently to the increased initial kinetic energy of the hot atoms. Most importantly, the strong interaction with surface electron−hole pairs, modeled using an electronic friction model, is shown to play an important role in rapid energy dissipation and significant retardation of the impulsive diffusion.

Short- and Long-Time Dynamics of Hydrogen Spillover from a Single Atom Platinum Active Site to the Cu(111) Host Surface

“…As expected, there are clearly two regions: one corresponding to the initial impulsive diffusion of the hot H* atoms ( t < 5 ps) and the other suggestive of conventional diffusion of a thermal H* atom at a longer time scale ( t > 20 ps). As expected, the former ballistic diffusion depends sensitively on the initial condition, such as the incidence energy and angle, as shown in our earlier publication . However, the latter self-diffusion has essentially an unchanged diffusion behavior for different initial conditions, also shown in Figure S3 in the Supporting Information.…”

“…Following the dissociation at the Pt site, we observed that one hydrogen typically undergoes facile hopping from the Pt site to Cu sites with increasing distances, similar to the behavior observed in the earlier theoretical work on Pd/Cu(111) by Busnengo and co-workers . However, our study suggested that the characteristic diffusion time and length of the adsorbed H* atom are strongly influenced by the interaction with the surface electron–hole pairs (EHPs) . The resulting electronic friction (EF) slows the spillover significantly, underscoring the importance of nonadiabatic effects. − Indeed, the importance of electronically nonadiabatic dissipation in H* diffusion in metals has been noticed before using model potentials. , More recently, nonadiabatic energy dissipation of H atoms in scattering from metal surfaces was observed experimentally and characterized theoretically. , Theoretical predictions of nonadiabatic energy dissipation for hot H* atoms on various metal surfaces have also been made by several groups. − …”

“…Theoretically, the lowering of the H 2 dissociation barrier on Cu surfaces by PGM dopants has been confirmed by DFT calculations. − In a recent publication, we discussed the initial H 2 dissociation and subsequent spillover dynamics of H* on a Pt/Cu(111) SAA surface, using ab initio molecular dynamics (AIMD) . Following the dissociation at the Pt site, we observed that one hydrogen typically undergoes facile hopping from the Pt site to Cu sites with increasing distances, similar to the behavior observed in the earlier theoretical work on Pd/Cu(111) by Busnengo and co-workers .…”

“…After equilibration of ∼3 ps, the simulation at the desired temperature was run for 10 ps, from which surface configurations were saved for the later QCT calculations. The impinging H 2 ( v = 0, j = 0) was simulated along the surface normal within a circle centered at the Pt site with a radius of r = 1.4 Å, since the reactivity drops to zero outside the circle due to the high barrier at Cu sites, as discussed in our previous work . The initial position of the impinging H 2 was placed 6.0 Å above the surface with its azimuthal orientation randomly sampled.…”

“…19 However, our study suggested that the characteristic diffusion time and length of the adsorbed H* atom are strongly influenced by the interaction with the surface electron−hole pairs (EHPs). 24 The resulting electronic friction (EF) slows the spillover signifi- cantly, underscoring the importance of nonadiabatic effects. 25−28 Indeed, the importance of electronically nonadiabatic dissipation in H* diffusion in metals has been noticed before using model potentials.…”