Equilibrium structure and Ti-catalyzed H-2 desorption in NaAlH4 nanoparticles from density functional theory

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    Abstract

    Improving the hydrogen ab- and desorption kinetics in complex hydrides is essential if these materials are to be used as reversible hydrogen storage media in the transport sector. Although reductions in particle size and the addition of titanium based compounds have been found to improve the kinetics significantly, the physical understanding remains elusive. Density functional theory is used to calculate the energy of the potential low energy surfaces of NaAlH4 to establish the equilibrium particle shape, and furthermore to determine the deposition energy of Ti/TiH2 and the substitutional energy for Ti@Al and Ti@Na-sites on the exposed facets. The substitutional processes are energetically preferred and the Na-vacancy formation energy is found to be strongly reduced in the presence of Ti. The barrier for H2 desorption is found to depend significantly on surface morphology and in particular on the presence of Ti, where the activation energy for H2 desorption on NaAlH4{001} surfaces can drop to 0.98 eV—in good agreement with the experimentally observed activation energy for dehydrogenation.
    Original languageEnglish
    JournalPhysical Chemistry Chemcal Physics
    Volume8
    Issue number42
    Pages (from-to)4853-4861
    ISSN1463-9076
    DOIs
    Publication statusPublished - 2006

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