Theoretical Insights into H2 Activation and Hydrogen Spillover on Near-Surface Alloys with Embedded Single Pt Atoms

Despite extensive studies of hydrogen spillover on single-atom alloy surfaces, a thorough understanding of the structure–activity relationship is still lacking. Here, we investigate H2 dissociation and diffusion of the dissociated H species on the near-surface alloys embedded with single Pt atoms using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The DFT results indicate that subsurface alloying with early transition metals (X) (Pt1-X/Cu(111)) can generally promote the initial hydrogen spillover but suppress the H2 dissociation process, showing an intractable trade-off effect. While the DFT-calculated H2 dissociation barrier on Pt1-Co/Cu(111) is higher than that on Pt1-Ni/Cu(111), the AIMD results show that the H2 dissociation probability on the Pt1-Co/Cu(111) surface is much higher than that on Pt1-Ni/Cu(111). The trajectory analysis shows that H2 molecules on Pt1-Co/Cu(111) can adopt a more convenient conformation for dissociation when approaching the so-called close-range physisorption zone (CPZ) due to the relatively flat topography of the potential energy surface, thus increasing the H2 dissociation probability compared to the case on Pt1-Ni/Cu(111). This work provides a clear picture for understanding the structure–activity relationships of H2 activation and hydrogen spillover over single-atom catalysts. More importantly, it highlights an overlooked but essential role of the dynamic orientation of the reactant in heterogeneous catalysis.