The hydrogen storage properties of the Ti decorated benzene-Ti-graphene sandwich-type structures. (12th January 2016) - Tang, Chunmei
Abstract: The density functional theory is used to study the hydrogen storage properties of the transition metal Ti decorated benzene-Ti-graphene(BTG) sandwich-type structures. The calculated binding energy (8.27 and 8.62eV) of the Ti atom to the hollow site of the zigzag and armchair substrate in the BTG sandwich-type structures are nearly double of the corresponding cohesive energy of metal Ti(4.85 eV/atom) and the binding energy of the Ti atom above the hollow site of the graphitic sheet(4.74 eV), consequently allowing the atomic dispersion of Ti atoms without clustering. Therefore, the adsorption of H2 molecules between by the Ti atoms in the sandwich-type structures will be experimentally feasible. The calculated average adsorption energies of molecular hydrogen around Ti in the sandwich-type structures are in the range of 0.27–0.41 eV, which intermediates between physisorbed and chemisorbed states(0.1–0.8 eV). The maximum H2 molecules adsorbed by each Ti in the BTG structure should be 2. The partial density of states and the difference charge densities explore that the Ti sites adsorb molecular hydrogen mainly through the well-known Dewar–Kubas interaction. The calculated desorption temperature and molecular dynamic simulation indicate that the sandwich-type hydrogenated structures are easier to desorb H2 molecules. Therefore, the Ti decorated BTG sandwich-type structures are appropriate for hydrogen storage at near-ambient conditions. Graphical abstract: The binding energy(Eb ) for the Ti atom to (6x6) armchair graphitic sheet and (4x7) zigzag graphitic sheet are a little smaller than the experimental cohesive energy of bulk Ti(4.85 eV/atom). Therefore, when more Ti atoms are adsorbed on the structure, the clustering of Ti atoms perhaps appear, which will hander the further hydrogen storage. However, the Eb for the Ti atom to the zigzag and armchair substrate in the two sandwich-type structures increase to 8.27 eV and 8.62 eV respectively, not only are much higher than the Eb of Ti-graphene structure, but also are nearly double of the experimental cohesive energy of bulk Ti(4.85 eV/atom). Therefore, the problem of metal aggregative to form the cluster is expected to be overcome in these two sandwich-type structures, and the materials will be stable for hydrogen storage. Moreover, The desorption temperature T D for two hydrogen molecules adsorbed benzene-Ti-graphene(BTG) structures are at the room temperature, suggesting that the hydrogen release at near-ambient temperature may be feasible. Highlights: Ti can bind stronger to the graphene in the sandwich structures and do not suffer from clustering. Each Ti atom of the stable sandwich structures can store two hydrogen molecules with the moderate average adsorption energy. The hydrogenated sandwich-type structures can release H2 molecules at room temperature.