| In pursuit of hydrogen storage systems that can be operated under ambient conditions and reversibly release and adsorb hydrogen, complex hydrides are investigated using first-principles calculations from three perspectives: thermodynamics, kinetics, and crystal structures. We examine the experimentally and computationally proposed crystal structures and the finite-temperature thermodynamics of dehydrogenation for the quaternary hydride LiZn2(BH 4)5. We identify the stable structure of LiZn2(BH 4)2. We calculate zero point reaction enthalpies for the first three LiZn2(BH4)5 decomposition steps, which are -19, +37, +74 kJ/(mol H2) respectively. Based on the example of LiZn2(BH4)5, we present a schematic illustration methodology to analyze decomposition pathways of hydrogen storage materials and propose a strategy that can efficiently adjust the hydrogen desorption energetics. The proposed strategy is to search for novel mixed reactants and mixed products simultaneously. We determine the energetic barriers for hydrogen dissociation and diffusion on the ideal Mg-terminated MgB 2 (0001) surface, as well as on surfaces containing transition metal dopants. The calculated dissociation barrier for H2 on the clean surface is 0.89 eV, and the surface diffusion barrier is 0.17 eV. We find Ni, Cu, and Pd are good catalytic candidates that can significantly decrease the activation barrier for the dissociation of H2, without sacrificing the already low diffusion barrier. We find the overall migration barrier for atomic hydrogen diffusion in MgB2 bulk is 0.22 eV, showing that rapid diffusion of hydrogen is possible even at moderate temperatures. We report the theoretically predicted structure of the amorphous aluminoborane compound AlB4H11, which explicitly shows a --[B3H7]--Al(BH 4)--[B3H7]-- polymer chain. We demonstrate that the experimentally observed structures of LiBH4 are lowest in energy in DFT and solve the discrepancy between computational and experimental ground state crystal structures of LiBH4. |
