Single-Atom Catalysts Supported by Graphene and Hexagonal Boron Nitride: Structural Stability in the Oxygen Environment

Despite ample studies devoted to single-atom catalysts (SACs) based on two-dimensional materials, their structural robustness under atmospheric conditions has not been addressed so far. Using density functional theory, we examined the structural stability of metal adatoms embedded into mono-atomic vacancies of graphene and hexagonal boron nitride (h-BN) in the presence of oxygen molecules. We considered 30 different elements from the periodic table, including early- and late transition as well as noble metals. We found that the highest stability occurs in SACs with a missing B atom in h-BN, utilized as the trapping site for metal adatoms. The structural stability is preserved for most of the transition metals embedded into mono-atomic vacancies of graphene. The least stable are SACs formed when metal binding occurs at the missing N atom in h-BN. We found that a general picture of the structural stability of SACs in the oxygen environment can be provided from the comparison of binding energies of O and metal atoms at three defected surfaces. A refined understanding of the structural stability of SACs requires coadsorption of metal and O atoms and a closer inspection of electronic properties of metal atoms and mono-atomic point defects at graphene and h-BN, which is also presented here.