Analysis of hydrogen storage in metal hydride tanks introducing an induced phase transformation Germain Gondor, Christian Lexcellent* Institut FEMTO-ST, De ´partement de Me ´canique Applique ´e (LMARC), Universite ´ de Franche-Comte ´, UMR CNRS 6174, 24 Chemin de l’Epitaphe, 25000 Besanc ¸on, France article info Article history: Received 10 March 2009 Received in revised form 8 May 2009 Accepted 9 May 2009 Available online 21 June 2009 Keywords: Hydrogen storage Phase transformation Kinetics Thermodynamics abstract Hydrogen absorption in a metal hydride tank is generally studied based on a heat and mass transfer analysis. The originality of this investigation is that the phase transformation from a solid (a phase) to hydride (b phase) solution is included in the hydrogen absorption mechanism. Toward this end, a modelling of the equilibrium pressure, composition (absorbed or desorbed hydrogen atoms per metal atoms), and isothermal curves of a LaNi 5 alloy is performed. Moreover, a kinetic model is developed taking into account the steps of hydrogen absorption and desorption (i.e., physisorption, chemisorption, surface penetra- tion, nucleation and growth of the hydride phase and diffusion). Simulations are then performed to show the impact of external conditions (hydrogen gas pressure and temperature) and parameter values (wall heat transfer, conductivities of gas and solid, viscosity, porosity, etc.) on refilling time. The physical nature of the phase transformation associated to the hydrogen storage remains an open problem. ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, a new challenge is to find and develop alternative energy sources to fossil fuels which are known to increase the global warming of the earth due to the emission of green- house-effect gases. One such alternative is hydrogen, which can be very attractive for use in electric vehicles [1]. However, the use of hydrogen as a fuel is currently limited due to storage and transportation problems. For this reason, metal hydride- based hydrogen storage systems are potentially interesting due to their high volumetric capacities, compactness, safety, etc. The knowledge of hydrogen absorption and desorption rates is a key point for technological applications of such systems and they depend completely on the heat and mass transfer characteristics of the hybrid bed [2]. Modelling proves to be very complicated because the molec- ular dissociative chemisorption of hydrogen on the sample surface depends on the atomic penetration of H from the surface to the bulk and the diffusion in the body [3–5]. Moreover inter- metallic compounds (Lanthanides, Alanates, Magnesium alloys, etc.) are the seat of a phase transformation during hydrogen absorption or desorption. In fact, with the increase of hydrogen content, the solid solution becomes a hydride phase with a latent heat associated to the phase transformation. The reverse phase transformation is observed during hydrogen desorption. The contribution of the ‘‘phase transformation’’ to the heat management problem in the hydride bed is of great importance. * Corresponding author. Tel.: þ33 381666052. E-mail address: christian.lexcellent@univ-fcomte.fr (C. Lexcellent). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.05.070 international journal of hydrogen energy 34 (2009) 5716–5725