First-Principles Study of the Interaction of Atomic and Molecular Chlorine with Graphene, Silicene, Phosphorene, and h-BN Monolayer.

The environmental stability of 2D monolayers is critical for their applications across various technology-related fields. These monolayers can degrade when exposed to gaseous components in the environment, so minimizing these degrading effects is essential. In this paper, chlorine exposure to the 2D monolayers, specifically graphene, silicene, phosphorene, and h-BN monolayer, is investigated using van der Waals corrected density functional theory. The results find that atomic chlorine chemisorbs on graphene, h-BN, silicene, and phosphorene with adsorption energies of -1.09, -0.65, -3.10, and -1.74 eV/atom, and bond distances of 3.0, 2.6, 2.2, and 2.1 Å, respectively. In contrast, molecular Cl exhibits physisorption with adsorption energies around -0.22 eV and bond distances ranging from 3.3 to 3.6 Å. NEB calculations show that Cl dissociative chemisorption is exothermic on buckled monolayers (silicene and phosphorene) and endothermic on planar monolayers (graphene and h-BN). On buckled surfaces, Cl dissociates after overcoming energy barriers of 2.0 eV for silicene and 3.2 eV for phosphorene, forming a stable chemisorbed state that is 0.9 eV lower than the physisorbed state. However, on planar monolayers, Cl remains in the physisorbed state because the dissociated chemisorbed state is ≈ 1.5 eV higher in energy. These differences are due to the weaker π-bonds in buckled monolayers, which make dissociation easier, while planar monolayers stabilize the molecular form.