Electrochemical properties of Ti2Ni hydrogen storage alloy

Abstract

In this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti2Ni 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 Ti2Ni 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 capacity 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 Ti2Ni 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.