Density Functional\nTheory Investigation of 2D Phase\nSeparated Graphene/Hexagonal Boron Nitride Monolayers; Band Gap, Band\nEdge Positions, and Photo Activity

Creating sustainable and stable semiconductors for energy\nconversion\nvia catalysis, such as water splitting and carbon dioxide reduction,\nis a major challenge in modern materials chemistry, propelled by the\nlimited and dwindling reserves of platinum group metals. Two-dimensional\nhexagonal borocarbonitride (h-BCN) is a metal-free alternative and\nternary semiconductor, possessing tunable electronic properties between\nthat of hexagonal boron nitride (h-BN) and graphene, and has attracted\nsignificant attention as a nonmetallic catalyst for a host of technologically\nrelevant chemical reactions. Herein, we use density functional theory\n to investigate the stability and optoelectronic properties of phase-separated\nmonolayer h-BCN structures, varying carbon concentration and domain\nsize. We find that, on average, a higher C content reduces the energetic\ncost of carbon inclusion per atom, as an increasingly graphitized\nnetwork lowers the overall energy of the structure. Using functional\nHSE06, we show how the electronic bandgap of h-BN can be reduced from\n5.94 to 1.61 eV with significant substitution of C in the domain (C\nat. % ∼ 44%) adding to the weight of evidence that suggests\nthese segregated h-BCN systems can easily be customized. We use the\nlocation of conduction and valence band edges with respect to the\npotentials of HER, OER and CO<sub>2</sub> reduction to assess the\ncatalytic suitability of these materials, identifying three structures\nwith appropriate band edges for these catalytic reactions. Finally,\nthe photoactivity of the structures is assessed through TD-DFT calculations,\nand we propose two candidates for photocatalysis based on the segregated\nh-BCN system.