Physi-Sorption of H₂ on Pure and Boron–Doped Graphene Monolayers: A Dispersion–Corrected DFT Study

Abstract

High-surface-area carbons are of interest as potential candidates to store H2 for fuel−cell power applications. Earlier work has been ambiguous and inconclusive on the effect of boron doping on H2 binding energy. Here, we describe a systematic dispersion−corrected density functional theory study to evaluate the effect of boron doping. We observe some enhancement in H2 binding, due to the presence of a defect, such as terminal hydrogen or distortion from planarity, introduced by the inclusion of boron into a graphene ring, which creates hydrogen adsorption sites with slightly increased binding energy. The increase is from −5 kJ/mol H2 for the pure carbon matrix to −7 kJ/mol H2 for the boron−doped system with the boron content of ~7%. The H2 binding sites have little direct interaction with boron. However, the largest enhancement in physi-sorption energy is seen for systems, where H2 is confined between layers at a distance of about 7 Å, where the H2 binding nearly doubles to −11 kJ/mol H2. These findings suggest that interplanar nanoconfinement might be more effective in enhancing H2 binding. Smaller coronene model is shown to be beneficial for understanding the dependence of interaction energy on the structural configurations and preferential H2 binding sites.

Keywords

• boron–doped graphene
• h₂ physi-sorption
• binding energy
• van der waals dispersion correction
• dft