Structural And Electronic Properties Of Hdrogen Storage In Lightweight Materials: First-principles Study

The strong demand for new clean energy has attracted the notice in materials for energy storage. Hydrogen storage in solids has been recognized as one of the most practical approaches for so long. It is indispensable to understand the fundamental properties of hydrogen storage materials, especially the electronic structure and elastic properties in order to improve their performance. In the present study, we have presented the results of Li-N-H, Li-Mg-N-H and y-AlH3 by using ab initio calculations.(1) The structural and electronic properties of Li2NH and LiNH2 have been investigated by ab initio calculations. The optimized coordinates of atom and the bond lengths and angles are in good agreement with the experimental data. By analyzing the overlap population and Mulliken population, we find that the interaction between N and H atom is strongly covalent characters, and the N-H interaction of LiNH2 is weaker than that of Li2NH. The valence bands in the density of stares are dominated by the presence of N sp and H s states. One and two band gaps were observed in the valence bands of Li2NH and LiNH2, respectively.(2) The structural and electronic properties of Li2Mg(NH)2 for hydrogen storage have been studied by ab initio calculations. The optimal unit cell parameters and the distance of N-H are determined, which are in good agreement with the experimental data. The bulk modules and the energies of zero pressure are obtained by using Murnaghan equation of states. The results show that the a-Li2Mg(NH)2 is a ground state configuration. The overlap population analysis shows that the N-Li/Mg ionic characteristics and N-H interaction of a phase are weaker than those ofβphase. The valence band is dominated by the presence of N s and p states, hybridized with the H s state.(3) The structural, elastic and electronic properties of y-AlH3 have been investigated by density functional theory. The optimized lattice constants, the coordinates of atom and the bond lengths and angles are in good agreement with the experimental data. By analyzing the overlap population and Mulliken population, we find that the interaction between Al and H atom is strongly ionic with weak covalent characters. The valence band in the DOS is dominated by the presence of H s and Al sp states. A small band gap is separated the valence band from-7.5 to-7.0 eV. The elastic constants and bulk modulus are calculated. The elastic constants C11, C22, and C33 are 102.3514,93.4176 and 135.3996 GPa, respectively. The bulk modulus of y-AlH3 is 49.2746 GPa.