Catalytic effect of ZrCrNi alloy on hydriding properties of MgH 2 Shivani Agarwal a,b, *, Annalisa Aurora a , Ankur Jain a,b , I.P. Jain b , Amelia Montone a a ENEA, C.R. Casaccia, FIM Department, Via Anguillarese 301, 00123 Rome, Italy b Centre for Non-Conventional Energy Resources, University of Rajasthan, Jaipur, India article info Article history: Received 29 July 2009 Received in revised form 12 September 2009 Accepted 12 September 2009 Available online 4 October 2009 Keywords: Hydrogen storage Magnesium hydride Ball milling X-ray diffraction Microstructures Kinetics Cycling Thermodynamics abstract MgH 2 nanocomposites with ZrCrNi alloy obtained by high energy ball-milling were studied as-milled and after several hydriding-deydriding cycles. The microstructure and morphology of the samples was characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns show that no phase formation between MgH 2 and elements of the alloys takes place during milling and after cycling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure- composition isotherms of these composites were obtained in the pressure and temperature range of 0.1–15 bar and 200–300  C respectively. The maximum reversible storage capacity was found to be 6.2 wt% at 300  C. Absorption/desorption kinetics data at pressures of 0.1–5.0 bar and temperatures of 275  C and 300  C show that an activation process of about 20 cycles at 300  C is necessary for stabilization of the kinetics and for achievement of the full hydrogen capacity. The thermodynamic parameters, i.e. enthalpy of formation and dissociation calculated using Van’t Hoff plots, were found to be 73.53 kJ mol 1 and 87.63 kJ mol 1 respectively, in agreement with MgH 2 data reported in literature. ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction Among the metals and alloys known for their potential use in hydrogen storage, Mg-based alloys have attracted much interest for their high hydrogen capacity and low cost [1]. However, slow reaction kinetics, high dissociation tempera- ture and a hard activation process are the main drawback of the Mg-based system. Mg-based materials treated by high energy ball milling in inert and active media possess better sorption kinetics and higher hydrogen capacity [2–4]. Hydrogen absorption properties of Mg-based systems can be improved by different approaches, i.e. by i) adding an alloying element like Mg 17 Al 12 [5], Mg 2 Ni [6], ii) formation of composite materials with different catalysts such as metals, alloy, intermetallic, oxides and carbon materials like LaNi 5 [7], MmNi 5 [8], FeTi 1.2 [9], ZrFe 1.4 Cr 0.6 [10], TiO 2 [11], Cr 2 O 3 [12], Nb 2 O 5 [13], carbon nano-tubes [14] and, iii) surface modifica- tion of Mg [15,16]. Liang et al. [17] first reported the superiority of MgH 2 –V composite over mechanically milled and unmilled MgH 2 due to the catalytic behavior of V. Among all the alloys used to prepare composites with Mg, Zr based AB 2 type alloys, in particular the Zr–Cr–Ni ternary alloy offer great improve- ment in the sorption behavior due to their high charging/ discharging rate [18–21]. Recently Dehouche et al [22] reported the hydrogenation properties of MgH 2 nanocomposites with different families of alloys. In the present work, we chose Zr– Cr–Ni ternary alloy to prepare the composite MgH 2 - 10wt%ZrCrNi and to explore its hydrogenation properties in more detail viz. in terms of its structural, morphological, kinetics and thermodynamic properties. * Corresponding author. Tel.: þ91 141 2701602; fax: þ91 141 2711049. E-mail address: shivaniphy@gmail.com (S. Agarwal). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.09.034 international journal of hydrogen energy 34 (2009) 9157–9162