Density Functional Theory Investigation of 2D Phase Separated Graphene/Hexagonal Boron Nitride Monolayers; Band Gap, Band Edge Positions, and Photo Activity

Abstract

Creating sustainable and stable semiconductors for energy conversion via catalysis, such as water splitting and carbon dioxide reduction, is a major challenge in modern materials chemistry, propelled by the limited and dwindling reserves of platinum group metals. Two-dimensional hexagonal borocarbonitride (h-BCN) is a metal-free alternative and ternary semiconductor, possessing tunable electronic properties between that of hexagonal boron nitride (h-BN) and graphene, and has attracted significant attention as a nonmetallic catalyst for a host of technologically relevant chemical reactions. Herein, we use density functional theory to investigate the stability and optoelectronic properties of phase-separated monolayer h-BCN structures, varying carbon concentration and domain size. We find that, on average, a higher C content reduces the energetic cost of carbon inclusion per atom, as an increasingly graphitized network lowers the overall energy of the structure. Using functional HSE06, we show how the electronic bandgap of h-BN can be reduced from 5.94 to 1.61 eV with significant substitution of C in the domain (C at. % ∼ 44%) adding to the weight of evidence that suggests these segregated h-BCN systems can easily be customized. We use the location of conduction and valence band edges with respect to the potentials of HER, OER and CO2 reduction to assess the catalytic suitability of these materials, identifying three structures with appropriate band edges for these catalytic reactions. Finally, the photoactivity of the structures is assessed through TD-DFT calculations, and we propose two candidates for photocatalysis based on the segregated h-BCN system.

Creating sustainable and stable semiconductors for energy conversion via catalysis, such as water splitting and carbon dioxide reduction, is a major challenge in modern materials chemistry, propelled by the limited and dwindling reserves of platinum group metals. Two-dimensional hexagonal borocarbonitride (h-BCN) is a metal-free alternative and ternary semiconductor, possessing tunable electronic properties between that of hexagonal boron nitride (h-BN) and graphene, and has attracted significant attention as a nonmetallic catalyst for a host of technologically relevant chemical reactions. Herein, we use density functional theory to investigate the stability and optoelectronic properties of phase-separated monolayer h-BCN structures, varying carbon concentration and domain size. We find that, on average, a higher C content reduces the energetic cost of carbon inclusion per atom, as an increasingly graphitized network lowers the overall energy of the structure. Using functional HSE06, we show how the electronic bandgap of h-BN can be reduced from 5.94 to 1.61 eV with significant substitution of C in the domain (C at. % ∼ 44%) adding to the weight of evidence that suggests these segregated h-BCN systems can easily be customized. We use the location of conduction and valence band edges with respect to the potentials of HER, OER and CO2 reduction to assess the catalytic suitability of these materials, identifying three structures with appropriate band edges for these catalytic reactions. Finally, the photoactivity of the structures is assessed through TD-DFT calculations, and we propose two candidates for photocatalysis based on the segregated h-BCN system