Physi-sorption of H 2 on pure and boron-doped graphene monolayers: A dispersion-corrected DFT study
Carbon based materials are of interest as potential candidates for H 2 storage. Earlier work has been inconclusive on the effect of boron doping on the energy of H 2 binding. However, earlier work has been inconclusive on the definitive effect of boron doping on the energy of H 2 binding, i.e. isosteric heats of adsorption (Qst). In this work, we completed a systematic DFT study to evaluate this effect, and found that doping graphene with boron provides only minor enhancement in H 2 binding. More importantly, the presence of the electron deficient boron into a graphene ring introduces a defect, such as terminal hydrogen or distortion from planarity, which creates hydrogen adsorption sites with slightly increased Qst. The increase is from ~ 5 kJ/mol H 2 for the pure carbon matrix to ~6 - 7 kJ/mol for the boron doped system. The more strongly bond H 2 is located near the defect and shows little direct interaction with the boron. Most significant enhancement is found in systems where H 2 is confined between layers at a distance of about 7Å. In this case, the H 2 binding nearly doubles, to ~10 kJ/mol for both pure, undistorted graphene, and the 2% boron doped system, containing tetrahedral C atom distortion. Interestingly, at higher doping levels of boron, we found that the Qst decreases compared to the all carbon materials. These finding suggest that interplanar nanoconfinement may be more effective way to enhance H 2 binding than boron doping.