Electrochemical properties of Ti2Ni hydrogen storage alloy

Abstract

International audienceIn this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti2Nialloy used as negative electrode in nickel-metal hydride batteries have been studied bydifferent electrochemical techniques. Several methods, such as, galvanostatic charge anddischarge, the constant potential discharge and the potentiodynamic polarization areapplied to characterize electrochemically the studied alloy. The studied electrodes areobserved before and after electrochemical tests at different temperatures by scanningelectron microscopy.The amorphous Ti2Ni is activated after five cycles and the achieved maximumdischarge capacity is about 67 mAh g_1 at ambient temperature. Despite the low values ofthe maximum discharge capacity and the cycling stability (17%) and the steep decrease ofthe discharge capacity after activation, this alloy conserves a good stability lifetime duringa long cycling. A good correlation is observed between the evolution of the discharge capacityand those of the redox parameters during a long cycling.The enthalpy change, the entropy change and the activation energy of the formationreaction of the Ti2Ni metal hydride are evaluated electrochemically. The found values ofthe 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