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  • Theoretical Studies of Aluminum Based Nano Scale Materials for Hydrogen Storage
  • Kennilegar Rannsóknir á Álríkum Nanóefnum Fyrir Vetnisgeymslu
  • Meistara
  • Hydrogen is, for many reasons, an appealing energy carrier. The main problem for
    using hydrogen as fuel in mobile application is the onboard storage. Many studies
    have been done on so called metal hydrides for the purpose of storing hydrogen.
    For a metal hydride system to fulfill its task of being a good hydrogen storage
    it needs to release the hydrogen close to 100◦ C and the gravimetric portion of
    hydrogen in the system should be high, at least 6 wt% Former studies done in the
    H. Jónsson group showed that hydrogen binds more strongly to Mg, compared
    to large crystalline MgH2 , if the Mg is in nano scale clusters. Unfortunately,
    for Mg the hydrogen binding energy is already to large for the MgH2 crystal.
    These results have motivated us to look at the hydrogen binding in nano scale Al
    clusters, since the alane crystal (AlH3 ) is thermodynamically unstable at room
    temperatures but has a very high gravimetric portion of hydrogen, 10.1 wt%
    We have studied the stability and structure of nano scaled aluminum and alu-
    minum hydride clusters with plane wave based density functional theory (DFT).
    The structures of Aln H3n clusters are surprisingly open and all aluminum atoms
    are connected through a hydrogen bridging bonds. These bridging bonds make
    the clusters very open and floppy. The binding energy of hydrogen in the alu-
    minum hydride clusters has been calculated for clusters with 2 to 30 Al atoms.
    As for MgH2 , the binding energy is larger for small clusters of AlH3 than for the
    crystalline material. A model has been fitted to our data, to predict the bind-
    ing energies of hydrogen for even larger clusters. By comparing the stabilities
    of the pure aluminum clusters to the stability of aluminum hydride clusters, one
    sees that the reason for the increase in binding energy is due to the fact that
    the pure aluminum clusters destabilize more than the aluminum hydride clusters
    with decreasing size.

  • 12.6.2009

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