The catalytic effect of titanium oxide based additives on the dehydrogenation and hydrogenation of milled MgH2

Magnesium hydride (MgH2) is considered to be one of the most promising options for a solid state hydrogen storage material. However, for practical use it is still imperative to find a convenient means of overcoming its slow kinetics and high stability. In this investigation, oxide materials based on TiO2 have been prepared from alkoxide precursors using a sol-gel route. When ball milled with MgH2. the titanium oxide based additives were found to result in significantly reduced onset temperatures of dehydrogenation and increased hydrogenation and dehydrogenation rates. Dehydrogenation onset temperatures as low as 257 degrees C were observed, which is over 100 degrees C lower than for milled MgH2 with no additives. In cycling experiments at 300 degrees C, between pressures of 1 x 10(-2) bar H-2 and 6 bar H-2, reaction rates for dehydrogenation and hydrogenation were found to be up to 15 times quicker than for milled MgH2 with no additives. The Ti based oxide additives were found to change the mechanism of dehydrogenation from milled MgH2 from one of surface control followed by contracting volume, to a two-dimensional Johnson-Mehl-Avrami nucleation and growth mechanism. (C) 2009 Elsevier B.V. All rights reserved.