International Journal of Hydrogen Energy 32 (2007) 4933 – 4938 www.elsevier.com/locate/ijhydene Studies on synthesis and dehydrogenation behavior of magnesium alanate and magnesium–sodium alanate mixture M. Sterlin Leo Hudson, D. Pukazhselvan, G. Irene Sheeja, O.N. Srivastava ∗ Department of Physics, Banaras Hindu University, Varanasi 221005, India Received 10 May 2007; received in revised form 22 July 2007; accepted 22 July 2007 Available online 27 September 2007 Abstract Magnesium alanate (Mg(AlH 4 ) 2 ) has been synthesized by mechanochemically activated metathesis reaction involving MgCl 2 and NaAlH 4 . Its dehydrogenation kinetics and storage capacity has been studied by using Sievert’s type apparatus. We have obtained dehydrogenation capacity of 2.7 wt% H 2 from Mg(AlH 4 ) 2 + 2NaCl during the first decomposition step at 140 ◦ C and 1.1 wt% H 2 during second step decomposition at 280 ◦ C. Efforts were carried out to reduce NaCl content from the product using Soxhlet extraction technique. The Soxhlet extracted product gives the total dehydrogenation capacity of 4.7 wt% H 2 . To enhance the storage capacity, we have synthesized a complex hydride consisting of mixture: x Mg(AlH 4 ) 2 + y NaAlH 4 (0 <x< 1,y  1). In the alanate mixture 0.5Mg(AlH 4 ) 2 + NaAlH 4 , the dehydriding temperature of NaAlH 4 gets lowered by ∼ 50 ◦ C (from 190 ◦ C to 140 ◦ C) with 4 times faster desorption kinetics. The total hydrogen liberated in 180 min from NaAlH 4 + 0.5Mg(AlH 4 ) 2 (+NaCl) mixture at 140 ◦ C has been observed to be 3.7 wt% H 2 .  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen storage materials; Thermal decomposition; Dehydrogenation kinetics; Storage capacity 1. Introduction Hydrogen is an attractive replacement for fossil fuels. It is renewable, non-polluting and can be produced from non- renewable and renewable energy sources. However, the ap- plication of this promising ideal energy carrier, especially in the transportation sector will emerge only if a suitable storage medium becomes available [1]. Solid-state hydrogen storage medium, the metal hydrides have high volumetric hydrogen capacity as compared to other storage options such as high pressure and liquid hydrogen storage. It has been found that hydrides offer an efficient and safe way for storing hydrogen. Nevertheless, high volumetric hydrogen storage capacity in most of these hydrides are being offset by their low gravimet- ric capacity, which is generally to be of the order of 1–2 wt%. One of the ways through which this difficulty can be nullified is by using high hydrogen content light weight alkali and al- kaline earth metal alanates, having hydrogen gravimetric ca- pacity > 5 wt%. These complex metal hydrides decompose and ∗ Corresponding author. Tel.: +91 5422368468; fax: +91 5422369889. E-mail address: hepons@yahoo.com (O.N. Srivastava). 0360-3199/$ - see front matter  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.07.068 liberate hydrogen at reasonable temperatures and pressures with the presence of suitable catalyst [1–6]. Presently these are being investigated widely for mobile applications. The interest for extensive research on alanates was triggered through the pioneering work of Bogdanovic and Schwickardi [3], which demonstrated fast desorption and reversibility of NaAlH 4 through doping of NaAlH 4 by Ti bearing compounds. Since then research is being conducted on many other complex light weight alkali metal alanates such as LiAlH 4 , Ca(AlH 4 ) 2 , Mg(AlH 4 ) 2 , LiMg(AlH 4 ) 3 and borohydrides like NaBH 4 , LiBH 4 , Zn(BH 4 ) 2 , etc. [3–12]. Among the various alanates, Mg(AlH 4 ) 2 has drawn significant attention in the recent time due to its high theoretical hydrogen capacity of 9.3 wt%. It was first synthesized by Wiberg and Bauer in 1950 using solvent mediated metathesis reaction [13]. Recently, Fichtner et al. have replicated the same technique for the synthesis of Mg(AlH 4 ) 2 and investigated for hydrogen storage applications [11,12]. An alternative method, mechanochemically activated metathesis reaction has been attempted by Mamatha et al. and synthesized successfully solvent free Mg(AlH 4 ) 2 [9]. One of the recent studies on Mg(AlH 4 ) 2 is that of Varin et al. [14], who have reported the reason for failure in the formation of