Electrochemical properties of Ti 2 Ni hydrogen storage alloy Bilel Hosni a,b,c,* , Chokri Khaldi a , Omar ElKedim c , Nouredine Fenineche b , Jilani Lamloumi a a Equipe des Hydrures Metalliques, Laboratoire de Mecanique, Materiaux et Procedes, Ecole Nationale Superieure d'Ingenieurs de Tunis (ENSIT), Universite de Tunis, 5 Avenue Taha Hussein, 1008 Tunis, Tunisia b IRTES-LERMPS/FR FCLAB, UTBM, Site de Sevenans, 90010 Belfort Cedex, France c FEMTO-ST, MN2S, UTBM, Site de Sevenans, 90010 Belfort Cedex, France article info Article history: Received 18 February 2016 Accepted 5 April 2016 Available online xxx Keywords: A long cycling Enthalpy and entropy changes Activation energy Redox parameters Electrochemical techniques Nickel-metal hydride batteries abstract In this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti 2 Ni alloy used as negative electrode in nickel-metal hydride batteries have been studied by different electrochemical techniques. Several methods, such as, galvanostatic charge and discharge, the constant potential discharge and the potentiodynamic polarization are applied to characterize electrochemically the studied alloy. The studied electrodes are observed before and after electrochemical tests at different temperatures by scanning electron microscopy. The amorphous Ti 2 Ni is activated after five cycles and the achieved maximum discharge capacity is about 67 mAh g 1 at ambient temperature. Despite the low values of the maximum discharge capacity and the cycling stability (17%) and the steep decrease of the discharge capacity after activation, this alloy conserves a good stability lifetime during a long cycling. A good correlation is observed between the evolution of the discharge ca- pacity and those of the redox parameters during a long cycling. The enthalpy change, the entropy change and the activation energy of the formation reaction of the Ti 2 Ni metal hydride are evaluated electrochemically. The found values of the enthalpy change, the entropy change and the activation energy are about 43.3 kJ mol 1 , 51.7 J K 1 mol 1 and 34.9 kJ mol 1 , respectively. Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Hydrogen may constitute the main energy vector in the future [1]. The key to using it effectively and safely is the research and development of novel storage systems. One of the best solutions is to store it at the solid state in the form of metal hydride, it is the main materials in the negative electrodes of nickel-metal hydride (Ni-MH) secondary batteries [2]. Addi- tionally, the Ni-MH batteries have attracted much attention due to their high energy density, good discharge ability at low temperature, long cycle life, no memory effect and environ- ment cleanness [3e8]. * Corresponding author. FCLAB Research Federation (FR CNRS 3539), 90010 Belfort Cedex, France. E-mail address: bilel.hosni@utbm.fr (B. Hosni). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2016) 1 e9 http://dx.doi.org/10.1016/j.ijhydene.2016.04.032 0360-3199/Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Hosni B, et al., Electrochemical properties of Ti 2 Ni hydrogen storage alloy, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.04.032