M. Tliha

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.

Electrochemical properties of the LaGaO3 perovskite-type oxide used as negative electrode in Ni/MH accumulators

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

Abstract The decrease of Cobalt content in alloy is very beneficial to reduce the production cost of the alloy, whereas the effect of Co on cycle life of the AB5-type hydrogen-storage alloys is extremely important. Therefore, it is interesting to investigate low-Co and/or Co-free AB5-type alloys in which Co was substituted by other elements. Iron is a key element in the development of low-Co AB5-type alloys. The aim of this work is to systematically investigate the effect of the real surface area on the all kinetic properties of a low-Co LaNi3.55Mn0.4Al0.3Co0.6Fe0.15 alloy under cycling using electrochemical impedance spectroscopy (EIS) technique. All kinetic properties of the electrode, such as exchange density, limiting current density, high-rate charge/discharge ability, cycle life time, electrocatalytic activity, and diffusion rate are related to the real surface area. During the EIS analysis, interestingly, we found that with increasing number of charge/discharge cycles, the metal hydride alloy powders undergo micro-cracking into smaller particles, and thus the real surface area of the alloy increases, which then influences the kinetic properties of the electrode reactions.

Electrochemical hydrogen storage properties of Ti 2 Ni alloy prepared by mechanical alloying

The nominal composition of the Ti2Ni alloy was synthesized, under argon atmosphere and at room temperature, using a planetary high-energy ball mill. The effect of the temperature on the hydrogen storage properties of this alloy was studied using different electrochemical techniques. The electrochemical cycling results show that the maximum discharge capacity was obtained after only one cycle independently of the temperature. The loss of the capacity became more important with temperature. The activation energy of Ti2Ni alloy, prepared by mechanical alloying for a milling time of 60h, is estimated to be equal to 8 kJ mol-1. This obtained value is slightly less than that found for the same alloy prepared by magnetic induction melting.