Journal of Alloys and Compounds 376 (2004) 180–185 Hydrogen production and crystal structure of ball-milled MgH 2 –Ca and MgH 2 –CaH 2 mixtures J.-P. Tessier a , P. Palau a,1 , J. Huot b,2 , R. Schulz b , Daniel Guay a,∗ a Lab. de Recherche Mat. Avances, INRS Énergie, Matériaux et Télécommunications, Université de Québec, 1650 Boul. Lionel-Boulet, C.P. 1020, Varennes, Que., Canada J3X 1S2 b Expertise Chimie et Matériaux, Institut de Recherche d’Hydro-Québec, 1800 Boul. Lionel-Boulet, Varennes, Que., Canada J3X 1S1 Received 15 November 2003; received in revised form 8 December 2003; accepted 8 December 2003 Abstract The structure and hydrolysis reaction of ball-milled MgH 2 –Ca and MgH 2 –CaH 2 mixtures was investigated in function of milling time and component proportion. The nanocomposites formed by milling show faster hydrolysis reaction as well as higher hydrogen yield compared to conventional polycrystalline materials. This improvement is due to the formation of calcium hydride upon milling and to the fine mixture that results from extensive milling. When the milling is performed on MgH 2 –20.3 mol% CaH 2 mixtures, the reaction yield reaches 80% after 30 min of hydrolysis. © 2004 Elsevier B.V. All rights reserved. Keywords: Chemical hydrides; Nanocrystalline materials; Hydrolysis; Irreversible hydrides 1. Introduction For widespread utilization of hand-portable proton ex- change membrane fuel cell (PEMFC), a compact, safe and inexpensive source of hydrogen must be designed. Hydroly- sis reactions could potentially serve this purpose. However, for most compounds, the reaction is either too violent (for ex- ample: LiAlH 4 ) or too slow to be convenient. Also, because of the practical non-reversibility of this means of generating hydrogen, the chosen materials should be of low cost. Chemical hydrides such as sodium borohydride (NaBH 4 ) or lithium aluminum hydride (LiAlH 4 ) can be used as hy- drogen generators [1]. However, one important drawback of this method is the need of using a catalyst to activate the re- action [2–4]. Recently, Matthews and coworkers [5,6] have investigated novel complex hydrides stabilized with organic ligands as a source of hydrogen for PEMFCs. Hydrogen ∗ Corresponding author. Tel.: +1-450-929-8141; fax: +1-450-929-8102. E-mail addresses: huot.jacques@ireq.ca (J. Huot), guay@inrs-emt.uquebec.ca (D. Guay). 1 Present address: Pechiney Centre de Recherches de Voreppe, 725 rue A. Berges, BP 27, 38341 Voreppe Cedex, France. 2 Co-corresponding author. production by steam hydrolysis of NaBH 4 was also investi- gated and found to meet the purity requirement for fuel cell applications [7]. However, the price and availability of these types of compounds may make their widespread use diffi- cult. Therefore, there is a need for the development of an in- expensive chemical hydride which has high hydrogen yield, and fast but controllable hydrogen release. Furthermore, the residual products should be environmentally friendly. In a previous paper it was shown that, compared to con- ventional materials, MgH 2 –Ca nanocomposites have hydrol- ysis kinetics greatly enhanced as well as much higher yield of reaction [8]. In this paper, we present a systematic in- vestigation of the structure and hydrolysis characteristics of ball-milled MgH 2 –Ca and MgH 2 –CaH 2 mixtures. Depend- ing on the phases present in the synthesized nanocompos- ites, the chemical reactions of interest are: Mg + 2H 2 O → Mg(OH) 2 + H 2 (1) MgH 2 + 2H 2 O → Mg(OH) 2 + 2H 2 (2) Ca + 2H 2 O → Ca(OH) 2 + H 2 (3) CaH 2 + 2H 2 O → Ca(OH) 2 + 2H 2 (4) 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.12.013