Hydrogen desorption properties of mechanically alloyed MgH2 composite materials

Composite H storage materials were produced by mechanical alloying of MgH2 with metallic additives La(Ni0.7Fe0.3)(5), Pd3Fe and (Fe0.8Mn0.2)Ti and with the non-metallic additive Si. The H desorption properties of these alloys were investigated by thermal desorption spectroscopy. The desorption spectra yielded maximum H desorption rates at about 500 K for MgH2 + La(Ni0.7Fe0.3)(5), between 510 K and 560 K for MgH2 + Pd3Fe and at about 570 K for MgH2 + (Fe0.8Mn0.2)Ti, compared to a maximum at about 720 K for pure MgH2 powder. These results showed that composite materials with metallic additives reveal enhanced desorption kinetics. In contrast, no shift of the desorption maximum to lower temperatures was obtained by mechanically alloying MgH2 + Si, Scanning electron microscopy investigations showed similar microstructures for all composite materials, with MgH2 covering the additive particles like a thin film of irregular thickness. Owing to these results, a model for the H desorption process was developed with a catalytic process at the MgH2-additive interface praying a major role. (C) 2000 Elsevier Science S.A. All rights reserved.