Chokri Khaldi

Electrochemical study of cobalt-free AB5-type hydrogen storage alloys

Abstract Cobalt-free AB5-type hydrogen storage alloys have been examined for the purpose of lowering MH raw material costs. The electrochemical measurements showed that the cobalt-containing LaNi3.55Mn0.4Al0.3Co0.75 alloy had a maximum capacity of 300 mA h/g at a rate of C/6. The capacity decrease was calculated by 5% after 20 cycles at C/6 rate with 100% depth of discharge (DOD). The cobalt-free LaNi3.55Mn0.4Al0.3Fe0.75 alloy showed a very good cycling stability, although the initial capacity ( 250 mA h/g at C/6 rate) was lower than that of the cobalt containing alloy. The capacity decrease of the cobalt-free alloy amounted to 1% after 20 cycles under the same rate and DOD. The mechanism of hydriding/dehydriding reaction on the alloy electrodes was also investigated using a constant potential discharge (CPD) and cyclic voltammetry (CV) techniques. The obtained values of the hydrogen diffusion coefficient DH, were, 2×10−8 and 1.1×10 −10 cm 2 s −1 for LaNi3.55Mn0.4Al0.3Co0.75 and 8×10−9 and 1.0×10 −10 cm 2 s −1 for LaNi3.55Mn0.4Al0.3Fe0.75, by CV and by CPD, respectively.

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.

The electrochemical performance of AB3-type hydrogen storage alloy as anode material for the nickel metal hydride accumulators

For the purpose of lowering the cost of metal hydride electrode, the La of LaY2Ni9 electrode was replaced by Ce. The electrochemical performances of the CeY2Ni9 negative electrode, at a room and different temperatures, were compared with the parent alloy LaY2Ni9. At room temperature during a long cycling, the evolution of the electrochemical capacity—the diffusivity indicator (DHa2

Electrochemical Study of the Cobalt-Containing and Non-Cobalt-Containing AB5 Alloys Used as Negative Electrodes in Nickel–Metal Hydride Batteries

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Preparation and characterization of zinc sulfide thin films through the sulfuration of sprayed zinc oxide thin films

)—the exchange current density, and the equilibrium potential were determined. At different temperatures, the electrochemical characterization of this alloy allowed the estimation of the enthalpy, the entropy, and the activation energy of the hydride formation. The evolution of the high-rate dischargeability was also evaluated at different temperatures. Compared with the parent LaY2Ni9 alloy, CeY2Ni9 exhibits an easy activation and good reaction reversibility. This alloy also conserves a good lifetime during a long-term cycling. A lower activation energy determined for this alloy corresponds to an easy absorption of hydrogen into this new alloy.

Doped zinc oxide thin films for photodetectors devices

In this work, we studied the hydrogen storage properties of the LaGaO3 perovskite-type oxide used as negative electrode in nickel-metal hydride batteries. The LaGaO3 perovskite-type oxide is synthesized by conventional sol-gel method and their phase structure and electrochemical properties are investigated systematically. X-ray diffraction (XRD) analysis shows that LaGaO3 perovskite-type oxide consist of single phase and crystallizes in the orthorhombic space group Pnma. The electrochemical properties of the LaGaO3 electrode are studied at 55°C using different electrochemical techniques (chronopotentiometry, chronoamperometry, voltamétrie cyclique). The corrosion properties of the LaGaO3 electrode also are evaluated at different state of charge at 55°C.

AC Impedance Behavior of LaNi3.55Mn0.4Al0.3Co0.6Fe0.15 Hydrogen-Storage Alloy: Effect of Surface Area

The thermodynamic parameters of LaNi3.55Mn0.4Al0.3Co0.75 and LaNi3.55Mn0.4Al0.3Fe0.75 alloys have been evaluated from the electrochemical isotherms determined by OCV method. A comparative study has been done between the parameter values deduced from the electrochemical OCV method and the solid–gas method. It was found that the difference can be explained by the electrochemical corrosion of these alloys in aqueous KOH electrolyte. The corrosion behavior of the LaNi3.55Mn0.4Al0.3Co0.75 and LaNi3.55Mn0.4Al0.3Fe0.75 electrodes after activation was investigated using the method of the potentiodynamic polarization. The evolution of corrosion current density and potential values as function of the state of charge (SOC), show that the total substitution of cobalt by iron leads to accentuate the corrosion process.