The Study Of Hydrogen Storage Mechanism For Material Based On Transition Metal

Hydrogen has been recognized as an ideal energy carrier to replace fossil fuels in 21st century. Recently, its commercial use as an alternate energy has substantial the most difficult challenge is how to safely, effectively and economically storage hydrogen. Conventional methods of hydrogen storage such as high-pressure gas, liquid or solid-state aren't ideal storage methods, and cannot fulfill future storage goals. Transition metals (TM) were shown to be very promising for hydrogen storage in terms of hydrogen binding strength and storage capacity at ambient conditions. Recently, intensive research has been done for designed high density hydrogen storage material based on transition metals. In this thesis, we investigate the hydrogen adsorption structure and mechanism on isolated 3d transition metal, and Sc,Ti , V , Pd decorated on (8,0) SWCNT based on first-principle calculations.We first study the hydrogen storage structure, ability and storage mechanism of isolated 3d transition metal. It is found that all of 3d TM can absorb 8 hydrogen moleculars with similar structures except Cu and Zn atom. Those ingesting results are determined by the hydrogen adsorption mechanism. The adsorption binding mechanism is (i) the hydrogen adsorption structure of 3d transition metal is determined by the electron arrange of d orbit, hydrogen adsorbed at the low charge density area. Hydrogen storage structure and their adsorption ability are determined by arrangement of the electron at d orbit of transition metals; (ii) the adsorption energy of hydrogen on 3d TM is determined by the electrostatic Coulomb attraction, which is induced by the electric field due to the charge transfer from metal 4s to 3d. It was found that all those adsorbed hydrogen molecules around the metal atoms form supercell structures, and further lowers the binding energy.The study of 3d TM showed that Sc,Ti and V have great ability of hydrogen storage, while carbon nanotube has light weight and high surface to volume ratios. We investigated the hydrogen adsorption and binding mechanism on transition metals (Sc, Ti, V) decorated (8,0) single walled carbon nanotubes. Our results show that non-filled shell TM (Sc, Ti, V) coated on SWCNTs can uptake over 8 wt.% hydrogen with the binding energy range in room hydrogen storage (about -0.54 eV), promising potential high capacity hydrogen storage material. While full filled shell TM Pd-decorated single-walled carbon nanotubes (SWCNT), the most hydrogen storage capacity is 2.88 wt. % for the uniformly Pd-decorated SWCNT. The result is good agreement with the experimental measurement, which also proved our method and model is valid.