Quantum Chemical Calculations on the Physisorption of Molecular Hydrogen on N-doped Graphene

Abstract

We have investigated the hydrogen storage ability of nitrogen substituted graphene, through studieson the adsorption by performing quantum chemistry calculations on the model system using the aug-cc-pVDZ basis set at MP2 level of correlation. The N-doped graphene surface was estimated underthe assuption that we have a random but fairly even nitrogen distribution throughout the surface,so the average interaction energy was calculated as a combination of the individual interactionenergies corresponding to nitrogens in orto, meta, and para position to eachother. We evaluatedthe interaction with molecular hydrogen over a range of different separations, and at three differentorientations. Nitrogen substitution was found to give a small, but positive effect on the adsorptionof hydrogen, in two of the considered orientations. The average interaction energy experiencedan increase of 3% from nitrogen substitution. We have also investigated the effect of applyingan external electric field in positive and negative x-, y- and z-direction. Using fields in differentdirections will be a good switch between adsorption and desorption. Small fields were found toonly slightly affect the adsorption of hydrogen. Large fields were found to significantly changethe adsorption, but it also induced changes of the ground state of the system. These excitationsremains to be thoroughly investigated. There is also the unanswered question of how strong fieldit is reasonable to apply, with respect to energy consumption and to how the field will disrupt thestable electronic structure of sp2 hybridized carbon bonds.