Density functional theory study of hydrogen storage by spillover on graphene and boron nitride sheet: doping effect and the kinetic issues
Date of Issue2012
School of Physical and Mathematical Sciences
The lack of efficient hydrogen storage materials has hindered the potential use of hydrogen as fuel for transportation, personal electronics and other portable power applications. Hydrogen spillover has been experimentally demonstrated to be an effective approach for hydrogen storage applications. To have a fundamental understanding of the hydrogen spillover mechanism, theoretical investigations on the doping effect and the kinetic issues of the hydrogen storage by spillover on graphene and boron nitride sheet have been carried out in this thesis. By incorporating boron into the graphene sheet, DFT calculations have shown that B-doping can effectively enhance the hydrogen adsorption strength of graphene. Compared with the undoped case, the metal catalyst (Pt4) has higher stability on B-doped graphene, where more H2 molecules can readily dissociate into H atoms on the supported metal cluster, which then serves as a steady H source for the subsequent H migration process. The estimated activation barrier for H migration from metal to substrate is much lower than that for the undoped case. The BC3 sheet with boron atoms uniformly distributed is then investigated. According to our calculations, the activation barriers for both H migration and diffusion on the BC3 sheet are less than 0.7 eV, thus more hydrogen can adsorb on B-doped graphene than on the pristine graphene under ambient conditions. Our theoretical result is a good support of the experimental findings that B-doped microporous carbon has an enhanced hydrogen storage capacity. With proper metal catalyst, the BC3 sheet could be a potential candidate of hydrogen storage material. Further investigations on the N-doped graphene show that the pyridinic-N doping is the favored method for hydrogen spillover rather than the graphitic-N doping. Higher stability of metal catalyst and more dissociated hydrogen can be obtained on the pyridinic-N doped graphene, compared with the graphitic-N doped case. The activation barrier for H migration from the Pt4 cluster to the pyridinic-N doped graphene is estimated to be around 1 eV, indicating that pyridinic-N doping could be an effective approach in modifying graphitic surface for hydrogen storage applications by H spillover, and further improvement on the H spillover kinetics for N-doped graphene is highly desired.
DRNTU::Science::Chemistry::Physical chemistry::Reactions and kinetics