Hydrogen Desorption from MgH 2 Based Nano-Micro Composites
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0971-Z08-07
Hydrogen Desorption from MgH2 Based Nano-Micro Composites Ennio Bonetti1, Anna Lisa Fiorini1, Luca Pasquini1, Nadica Abazovic2,3, Amelia Montone2, and Marco Vittori Antisari2 1 Department of Physics, University of Bologna, Viale Berti Pichat 6/2, Bologna, 40127, Italy 2 Materials and Technology Unit, ENEA C.R. Casaccia, Roma, 00100, Italy 3 Institute for Nuclear Sciences Vinca, Belgrade, Serbia, 11000, Yugoslavia
ABSTRACT The microstructure and hydrogen sorption behaviour of MgH2 based nano-hydrides with different additives prepared by ball milling and inert gas condensation has been investigated by XRD, Differential Scanning Calorimetry and Mechanical Spectroscopy. Preliminary results on materials with similar composition and different nanostructures show that suitable mechanical processing and additive additions induce in the nanostructured composites tailored channels for improved ab/de-sorption kinetics at reduced temperatures. INTRODUCTION In recent years an increasing research activity was developed aiming at the optimisation of the functional properties of magnesium hydrides for hydrogen storage applications. Some investigations have explored the critical issues preventing a practical employment of these materials with fuel cell technology. Indeed the applications involving polymer electrolyte fuel cells (PEFC) demand an hydrogen de-sorption temperature from solid state hydrides compatible with the fuel cell waste heat, in the range 320-430 K. Recently the preparation of nano-hydrides by ball milling techniques in a controlled environment and with further addition of a dispersion of submicro-nanoparticles of different additives such as transition metals, intermetallics or oxides, allowed the achievement of faster sorption kinetics at reduced temperatures [1-6]. At the same time the hydrogen sorption properties were investigated on model systems as Mg-Pd multilayers prepared by vacuum evaporation [7] or Nb–doped Mg films deposited by rf magnetron sputtering [8,9]. Phenomenological models to explain the observed improved kinetics of hydrogen sorption have been advanced taking into account several factor such as the hydride grain-particle size [10], the presence in these nanosystems of a relevant surface area of oxide layers [11], the metal oxide particles dimension [12], the catalytic effect of some additives [13,14], the thermal stability of the nanostructured hydrides against repeated ab/de-sorption cycles [15,16]. Even if the detailed role of additives and the mechanisms of hydrogen in/out diffusion at the atomic scale remain still not completely clarified, the whole of these researches indicate that suitable processing of MgH2 based nanocomposites is the way to tailor hydrogen desorption channels with improved desorption properties, requiring cheaper and not strictly clean processing [17]. Here we present some preliminary results aiming to obtain a phenomenological modelling of hydrogen mobility ( sorption behaviour) on MgH2 based nanocomposites, on which we had previously acquired systematic
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