First principles study to identify the reversible reaction step of a multinary hydrogen storage “LieMgeBeNeH” system Pabitra Choudhury a,b , Venkat R. Bhethanabotla a,b, *, Elias Stefanakos b a Sensors Research Laboratory, Department of Chemical and Biomedical Engineering, University of South Florida, 4202 E Fowler Ave., ENB 118, Tampa, FL 33620, USA b Clean Energy Research Center, College of Engineering, University of South Florida, 4202 E Fowler Ave., ENB 118, Tampa, FL 33620, USA article info Article history: Received 10 February 2010 Received in revised form 15 May 2010 Accepted 24 May 2010 Keywords: Hydrogen storage Complex hydrides Density functional theory Lattice dynamics Thermodynamics abstract A density functional theory study with the generalized gradient approximation (GGA) and projected augmented wave (PAW) method is performed for the hydrogen storage proper- ties of the complex multinary storage LieMgeBeNeH system. Using ab initio methods, stability of the structures at finite temperatures is confirmed via. phonon spectrum calculations. Thermodynamic properties such as heat of reaction, and Gibbs energy for each reactant and product in the reaction steps in different temperature zones are calculated. It is found that reversibility occurs in the temperature range of 160e225  C with approximately 4.38 wt % hydrogen storage capacity. The enthalpy of reversible re-/de- hydrogenation is found to be 55.17 kJ/mol H 2 , which is supported by experimental data. The total hydrogen storage capacity of this material is calculated to be 8.76 wt% from the desorption behavior observed at different temperatures up to 350  C. These theoretically established reactions are validated with the suggested mechanism from experimental observations for the dehydrogenation reaction of this LieMgeBeNeH multinary system. These efforts are expected to contribute toward identification of suitable hydrogen storage materials. ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction Metal/complex hydrides as hydrogen storage material have gained importance in the past few years due to rising fuel costs and ease of on-board storage. The individual storage properties of metal/complex hydrides were found to improve in their combinations [1,2]. The undesired properties of these hydrides like ammonia liberation [3] or diborane liberation [4,5], poor kinetics and irreversibility were overcome by their binary systems [6]. Many experimental and theoretical studies have been carried out to find materials with reversible prop- erties, low desorption temperatures, accelerated kinetics and optimum hydrogen storage capacity (at 298 K, the US revised DOE system target for gravimetric hydrogen storage capacity is 5.5 wt % by 2015) [7e15]. Experiments suggest that complex hydrides of Li, Na, Mg, B, Al and N have such properties [6]. It is well known that individual hydride such as LiBH 4 , LiNH 2 and MgH 2 starts dehydrogenation at very high temperature but the combination of these hydrides system starts releasing hydrogen at much lower temperature. Solid-state synthesis pertaining to destabilization of LiBH 4 [16], LiNH 2 [17] and LiBH 4 /LiNH 2 [18] with MgH 2 has been found to enhance the reversible hydrogen storage characteristics. The LiBH 4 eLiNH 2 system fails to re-hydride due to its relatively small dehy- driding enthalpy, and suggests that hydrogen release from the system is a kinetically e rather than thermodynamically e * Corresponding author. Sensors Research Laboratory, Department of Chemical and Biomedical Engineering, University of South Florida, 4202 E Fowler Ave., ENB 118, Tampa, FL 33620, USA. Tel.: þ1 813 974 2116; fax: þ1 813 974 3651. E-mail address: venkat@eng.usf.edu (V.R. Bhethanabotla). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 35 (2010) 9002 e9011 0360-3199/$ e see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.05.097