Wombat
Drew Sheppard, Mark Paskevicius and Craig Buckley from Curtin University of Technology have been using WOMBAT to investigate the potential of MgH2 as a low-weight, high-capacity hydrogen-storage material for use in on-board vehicle fuel replacement systems.
The adsorption of H2 by Mg and the generation of MgH2 is highly endothermic and does not occur at room temperature. The thermo-dynamics of this reaction are made more favourable by the addition of Si to the reaction pathway, allowing H2 sorption to occur at temperatures and pressures more conducive to vehicular storage:
2MgD2 + Si ó Mg2Si + 2D2
Unfortunately, this modification kinetically hinders the regeneration of H2 below 200 °C. By implementing a high pressure gas cell and a series of adjacent heat lamps to heat the sample stepwise to 350 °C over 48 h, in-situ neutron diffraction patterns were obtained during the decomposition of MgD2 in the presence of Si. The kinetics of MgD2 decomposition and the crystallite sizes of MgD2, Si, and Mg2Si determined from the diffraction data are of vital importance in explaining the nature of the extreme kinetic barrier that restricts D2 sorption. Once understood, further modifications to the system are envisaged that will improve the viability of MgH2 as a hydrogen-storage medium.
Left: Mark Paskevicius (left) and Drew Sheppard (right) using gas-loading equipment and heating lamps on WOMBAT; Right, in-situ powder diffraction pattern illustrating the decomoposition of MgD2.