Journal of Alloys and Compounds 497 (2010) L17–L20 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Letter High capacity hydrogen generation on-demand from (NH 3 + LiAlH 4 ) Weifang Luo ∗ , Donald Cowgill, Ken Stewart, Vitalie Stavila Sandia National Laboratories, Livermore, CA 94551, USA article info Article history: Received 21 October 2009 Received in revised form 1 March 2010 Accepted 2 March 2010 Available online 9 March 2010 Keywords: Hydrogen generation Ammonia Metal hydrides Exothermic reaction abstract Hydrogen storage materials with high capacity are highly desirable. Currently none of the existing storage materials can meet the requirement of motor vehicle applications. We report a new hydrogen storage generation system, LiAlH 4 + NH 3 . The two components are stored in separate containers when there is no demand for hydrogen, while the two components mix, hydrogen can be generated, up to 13 wt.% H 2 at ambient temperature, on-demand. The H 2 formation is exothermic with a high rate, suggesting that this is unlikely to be a reversible hydrogen storage material. More investigation is needed to improve or to maximize the degree of conversion. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Currently existing reversible hydrogen storage materials can deliver hydrogen not more than 5 wt.%, which is below the require- ment for vehicular applications. Some other materials are able to deliver larger amounts of hydrogen, but they cannot be recharged on-board. For example, AlH 3 can deliver about 10 wt.% of H 2 at around 373 K [1,2], which is suitable for vehicular application. This type of materials deserves more attention. A hydrogen generation system has been reported using the NH 3 + LiAlH 4 reaction at ambient temperature to provide H 2 to feed a fuel cell [3,4]. The electric power output from the fuel cell was reported to be as much as 483 Wh/kg. In this device H 2 was gen- erated by passing NH 3 , stored in one container, through the LiAlH 4 in a separate container. A check valve between the two containers shut the NH 3 flow off when the pressure in the LiAlH 4 -container exceeded a preset value. This clever design enables H 2 release on- demand. The following reaction was used by Sifer and Gardner [4] to describe hydrogen formation: 4NH 3 + 3LiAlH 4 = Li 3 N + 3AlN + 12H 2 (1) In this reaction all of the hydrogen contained in these two com- pounds is converted to H 2 , giving a theoretical capacity of 13.2 wt.%. Since the authors’ main focus was on the hydrogen generation device design and its power output efficiency determination, they ∗ Corresponding author at: Sandia National Laboratories, Analytical Materials Sci- ence, 7011 East Ave., MS9403, Livermore, CA 94551, USA. Tel.: +1 925 294 3729; fax: +1 925 294 3410. E-mail address: wluo@sandia.gov (W. Luo). did not provide experimental proof for the reaction (1). Their paper is the sole report currently in the literature that uses this reaction for H 2 generation. The two-component system, LiAlH 4 + NH 3 , is a good candidate system for hydrogen generation since the two components are sta- ble enough to meet the safe-storage requirement when there is no demand for power, but can also deliver H 2 on-demand at ambient temperature by mixing the two active components. Both LiAlH 4 and NH 3 contain high weight percentages of hydrogen, 11 wt.% and 17 wt.%, respectively. The fluid component, anhydrous ammo- nia, permits both the mixing and the flow-control straightforward. Ammonia has a boiling temperature of 239 K and a vapor pressure of 50 × 10 5 Pa at 298 K and, therefore, it can be readily liquefied to attain a high volumetric density. This allows easy rapid re-fill with high volumetric density, avoiding the need for high pressure. The metal hydride, LiAlH 4 , is selected as the other component because of its reactivity. The cost of NH 3 is low as its mass production tech- nology is mature. LiAlH 4 contains only elements that are abundant and the cost could be low when the manufacture technology is developed and the market need emerges. Other two-component systems, such as (NaBH 4 +H 2 O) [5,6] and (LiH + NH 3 ) [7] have been intensively reported in the literature while the (LiAlH 4 + NH 3 ) system still remains under-investigated. The current research effort focuses on identifying all possible reactions and products as well as the reaction conditions for the (LiAlH 4 + NH 3 ) system. We also will discuss the reaction rate and efficiency limitations for applications of interest. 2. Experimental NH3 (Matheson, 99.999%) and powdered LiAlH4 (Alfa Aesar, >95%) were used without pretreatment. Co(NO3)2·6H2O (Alfa Aesar, >95%) was used as NH3-filtering 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.03.040