The Investigation Of Boron-Based Nanostructure Materials For Hydrogen Storage

Hydrogen is viewed as the most promising alternative fuel that could one day replace fossilfuels because of its high density and cleanness and it is considered as one of the mostimportant new energies in the21stcentury. However，it is a difficult problem for hydrogenstorage. In general, hydrogen is stored through compression, liquefaction, or adsorption inmetallic compounds and complex hydrides, with high pressure and low temperature. It doesnot only consume a lot of energy, but also causes safety problems. In order to overcome thesechallenges, the most possible way is to find materials that can store hydrogen with highgravimetric and volumetric density at near ambient thermodynamic conditions. So, thedevelopment of novel materials for hydrogen storage will become an irresistible general trendin realizing hydrogen economy. Ideal hydrogen storage materials for mobile applicationsrequire the host material to be light and to be operated at near-ambient thermodynamicconditions.To realize reversible hydrogen storage at room temperature, a binding energy of about19.3-38.6kJ/mol（0.2-0.4eV） per H2molecule is needed for the hydrogen storage materials.In a recent theoretical study, Zhao et al. predict a low-energy single-walled scandium triboride（ScB₃） nanotube that the Sc atoms are embedded in the wall and all the boron atoms have5-fold coordination. Their calculation shows that the energy of the Sc-embedded ScB₃nanotube is77.2kJ/mol（0.8eV） per ScB₃unit lower than the Sc-coated one. In suchSc-embedded ScB₃nanotube, each boron atom binds one atomic H and each Sc atom bindsone dihydrogen molecule, resulting in a total hydrogen capacity of6.1wt%with a bindingenergy of22-26kJ/mol. We have calculated （ScB₃）n（n=2-7） nanotubes and our results showthat some special B atoms maybe absorb one H atom，but binding energy is too large. Each Scatom can absorb at least two dihydrogen molecule through Kubas coordination （13.8-25.7kJ/mol）, resulting in a total hydrogen capacity of5.0wt%and the most hydrogen capacity of6.6wt%. In addition, we predict one kind of stable B180, and is doped with some metal atoms,the stable B₁₈₀Ca₁₂is found finally. B₁₈₀Ca₁₂is also one novel material for hydrogen storage.Base on our results, we believe that （ScB₃）n、B₁₈₀Ca₁₂can be used as building blocks toconstruct hydrogen materials with high storage capacity at room temperature and modestpressure. Our results can provide some guidance for the designing and future experiment ofmetal atoms doping nanostructured hydrogen storage materials.