Theoretical Studies Of Hydrogen Storage Materials Based On Metal-organic Carbide

Hydrogen is viewed as a source of clean energy to take place of petroleum fuels in the future as petroleum fuels have very long reproducing cycle (if it has), polluting nature, and green house effect. Hydrogen is light and is not feasible be compressed as the intermolecular interaction is the weak van der Waals (vdw) force. Thus, it is crucial to develop safe, economical, and practical means to store hydrogen. An ideal hydrogen storage material should have binding energies between hydrogen molecule and adsorbents higher than simple vdw interaction and substantially lower than chemical bond for better adsorption and desorption.Our work includes the following sections. Firstly, we explored the possibility of applying the non-dissociative H2 adsorption mechanism to Transition-Metal-Methylidynes, TMCH (TM=Sc, Ti, V, and Cr) because of its merit of light weight. We discussed the capacity of hydrogen adsorption of TMCH, which includes the H2 binding energies and maximal number of H2 that the complexes can adsorb. We also discussed the dimerization and oligomerization of ScCH and hydrogen storage capacity of the most stable structures, respectively. The corresponding gravimetric density decrease to 9.2wt% and 7.9wt%.Secondly, corannulene (C20H10) was chosen as a candidate for hydrogen storage. Corannulene is a bowl shaped molecule with higher electron density in peripheric-carbon atoms than in inner-carbon atoms. Both theoretical and experimental results indicate that corannulene may offer some advantages over single-wall carbon nanotubes or graphite nanofibers. In this work, we devise that Sc for our investigation due to its severe electron-deficient effect and can be dihydrogen sorption center. We reported three different doping where Sc atom substituted the C atom at the hub, rim-quat and rim positions, respectively. According to NBO, FMO, and LDOS analyses, we noted that the adsorption of hydrogen molecule would not destroy the stability of Sc-substituted corannulene. The conductivity of the Sc-substituted corannulene decreased when one or more hydrogen molecule is adsorbed. The hydrogen storage ability of C19ScH10 and the dimer were investigated.Thirdly, we explored to parameterize H and Li elements using SCED-LCAO. For the parameterization of H, one should recognize that the existing SCED-LCAO framework is not expected to work very well on column I elements such as lithium and hydrogen because the electronic wave functions for column I elements are more delocalized. We tested this scenario by intentionally optimizing the SCED-LCAO parameters in the existing framework for hydrogen using the database set composed of C/H-based clusters. We found that reasonable optimization results could be achieved only if the on-site energy of hydrogen is treated as one of the optimized parameters. The resulting value was dramatically shifted from the ground state orbital energy of -13.6 eV for an isolated hydrogen atom to the value of -4.6 eV in an atomic aggregate consisting of hydrogen and carbon atoms. This dramatic energy shift is an indication that the electron in the ground state of the isolated hydrogen atom is now being excited to excited states in the presence of nearby neighbors in an atomic aggregate. We modified the SCED-LCAO Hamiltonian to address this effect in order to develop a flexible strategy that can be used to a wide range of elements in the periodic table, from elements with more localized electron wave functions to those with delocalized electrons.Combining with optimal gravimetry and kinetics analysis, the predictions mentioned above may provide useful guidance for devising possible schemes by which the novel hydrogen storage material can be manipulated.