Hydrogen complexes on single-atom alloys: A combined DFT – Kinetic Monte Carlo study

Single-Atom Catalysts (SACs) are a new class of solid catalysts with potential applications in a wide spectrum of chemical reactions. The family of Single Atom Alloys (SAAs) is promising for hydrogen-related reactions. One interesting aspect of SACs is that their chemistry is reminiscent of coordination chemistry, and a pertinent example is the formation of dihydrogen complexes in hydrogen-related reactions with similarities to coordination compounds. The formation of these hydrogen complexes has been suggested also for SAAs, based on density functional theory (DFT) calculations. In this work, we conducted a study combining DFT with Kinetic Monte Carlo (KMC) to investigate the formation of hydrogen complexes on a set of SAAs. We scrutinized 14 SAAs with DFT and performed KMC simulations on three relevant cases. Our study considers explicitly the kinetic barriers for the formation and decomposition of these complexes to elucidate the kinetics of the adsorption of molecular H2 on SAAs. The results indicate that the new species can be relevant depending both on their stability and the reaction barriers involved. In particular, we focused on three test cases, Co@Rh(111), Pd@Rh(111) and Co@Au(111) showing that the formation of dihydrogen species, H2*, where * indicates an adsorbed complex, can affect the formation of the complex from molecular H2.