Thermal decomposition of non-catalysed MgH 2 ﬁlms M. Barawi a, *, C. Granero a , P. Dı´az-Chao b , C.V. Manzano c , M. Martin-Gonzalez c , D. Jimenez-Rey d , I.J. Ferrer a , J.R. Ares a , J.F. Ferna ´ ndez a , C. Sa ´ nchez a a MIRE-Group, Laboratorio de Fı´sica de Materiales de Intere ´s Energe ´tico, Dpto. de Fı´sica de Materiales, Facultad de Ciencias, UAM, 28049 Madrid, Spain b CRISMAT, UCBN, ENSICAEN, 6 Boulevard du Mare ´chal Juin, 14050 Caen Cedex, France c IMM e Instituto de Microelectro ´nica de Madrid (CNM-CSIC), Isaac Newton 8, PTM, Tres Cantos, E-28760 Madrid, Spain d Centro de Microana ´lisis de Materiales (CMAM), C/Faraday 3, UAM, 28049 Madrid, Spain article info Article history: Received 14 November 2013 Received in revised form 18 December 2013 Accepted 6 January 2014 Available online xxx Keywords: Hydrogen storage Magnesium hydride Nanocrystalline ﬁlm Raman-spectroscopy Thermal decomposition mechanism Magnesium disilicide abstract Nanocrystalline Mg ﬁlms with thicknesses between 45 and 900 nm were prepared by e- beam on fused-SiO 2 substrates and hydrogenated at 280  C to investigate the H-absorption/ desorption process. Films were characterized by XRD, RBS, Raman, FEG, “in situ” optical measurements and TPD-MS. Whereas practically full conversion into MgH 2 is observed in thinner ﬁlms (d < 150e200 nm), higher amount of hydrogen is not absorbed by thicker ﬁlms (d > 200e250 nm) that is attributed to the formation of Mg 2 SieMgO phases (observed by RBS and Raman) as well as the slow kinetics of MgH 2 formation. H-desorption process is controlled by a nucleation and growth process and hydrogen is released at lower desorp- tion temperatures (T d ¼ 425  C) than bulk MgH 2 . T d are slightly lower (DT w 25  C) in thickest hydrogenated ﬁlms (d > 200e250 nm) suggesting an inﬂuence of Mg 2 Si and MgO phases, formed during hydrogenation. Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Magnesium (Mg) is able to accumulate high amounts of hydrogen (7.6 wt%) but its high stability and slow H-kinetics preclude its use for transport purposes [1]. To solve those drawbacks, Mg-nanostructures [2], with short H-diffusion pathways and size-effects which may destabilize the hydride, are being extensively investigated. Particularly, Mg ﬁlms [3] seem to be more adequate to obtain detailed information about the inﬂuence of thickness, microstructure and surface state on H-absorption/desorption mechanism than others synthesized nanostructures. To avoid the high temperatures and moderate pressures required to get magnesium hydrogenated, Mg ﬁlms are habitually capped by a Palladium (Pd) layer [3e5] (Pd enhances the H 2 -dissociation and HeH recombination processes and avoids the hydroxide/oxide formation) but research has * Corresponding author. Tel.: þ34 (0) 914975627. E-mail address: mariam.barawi@uam.es (M. Barawi). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2014) 1 e6 Please cite this article in press as: Barawi M, et al., Thermal decomposition of non-catalysed MgH 2 ﬁlms, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/j.ijhydene.2014.01.030 0360-3199/$ e see front matter Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2014.01.030