H. Mathlouthi

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review

This paper reviews the present performances of intermetallic compound families as materials for negative electrodes of rechargeable Ni/MH batteries. The performance of the metal-hydride electrode is determined by both the kinetics of the processes occurring at the metal/solution interface and the rate of hydrogen diffusion within the bulk of the alloy. Thermodynamic and electrochemical properties for each hydride compound family will be reported. The steps of hydrogen absorption/desorption such as charge-transfer and hydrogen diffusion for evaluating the electrochemical properties of hydrogen storage alloys are discussed. Exchange current density (I0) and hydrogen diffusion coefficient (DH) are the two most important parameters for evaluating the electrochemical properties of metal hydride electrode. The values of the two parameters for a number of hydrogen storage alloys are compared. The relationship between alloy composition and electrochemical properties is noted and evaluated.

Effect of partial substitution of co with Fe on the properties of LaNi3.55Mn0.4Al0.3Co0.75-xFex (x=0, 0.15, 0.55) alloys electrodes

Abstract The effect of iron substitution on the electrochemical behaviour of LaNi3.55Mn0.4Al0.3Co0.75−xFex compounds (x=0, 0.15, 0.55) has been studied by chronopotentiometry and cyclic voltammetry techniques. The maximum capacity decreases linearly from 308 to 239 mAhg−1 when the iron content increases from 0 to 7.3 wt.% (x=0.55). This decrease can be explained by the corrosion of the alloy in the aqueous KOH electrolyte. In spite of this decrease and of the long time needed for the activation, a good stability of discharge capacity was observed in LaNi3.55Mn0.4Al0.3Co0.75−xFex compounds. The reversibility of the electrochemical redox reaction of LaNi3.55Mn0.4Al0.3Co0.75−xFex alloy electrodes has been observed in the alloys least rich in iron. The hydrogen diffusivity in LaNi3.55Mn0.4Al0.3Co0.75−xFex alloy electrodes decreases when increasing the iron content. The obtained values of the hydrogen diffusion coefficient DH, varies between 2.1×10−7 and 8.2×10−9 cm2 s−1 depending on the iron content of the electrode.

Electrochemical properties of the LaY 2 Ni 9 hydrogen storage alloy

The electrochemical properties of LaY2Ni9 hydrogen storage alloy have been studied through chronopotentiometric, chronoamperometric and cyclic voltammetry measurements. At the C/5 rate the maximum capacity is obtained after 5 cycles of activation and reached 224 mAh g-1, the discharge capacity loss (ratio of the discharge capacity at a given cycle n by the maximum discharge capacity) tends to 46% after 100 cycles. The value of the hydrogen diffusion coefficient obtained through chronoamperometric technic, after a long cycling, is 1.3 10-7 cm2.s-1. The corrosion paramètres, such as the corrosion potential and the corrosion current density, are determined by cyclic voltammetry with a potential scanning rate of 1mVs-1. The evolution of the corrosion potential and the corrosion current density after a long cycling stabilize around an oscillating value of 1020 mV and 1.54 mA.cm-2, respectively.