Electrochemical properties of the LaNi4Fe compound elaborated by mechanical alloying

Abstract

In this paper, we have studied the electrochemical properties of the LaNi4Fe compound obtained by mechanical alloying (MA) for two durations 5 and 10 h. The properties of hydrogen absorption/desorption in the material are studied by using several characterization methods namely: The cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The values of the hydrogen diffusion coefficients obtained by cyclic voltammetry for the two alloying durations 5 and 10 h are equal to 2.7 10-9 cm2 S-1 and 5.7 10-9 cm2 S-1 respectively. The chronoamperomety show that the radius “a” of the particles which participate in the electrochemical reaction of the LaNi4Fe compound for the two grinding times 5 and 10 h are respectively estimated at 8 and 11 µm. Impedance spectra from experiments was used to describe the electrochemical processes that occur at the electrode-electrolyte interface. The electrochemical mechanism at the electrode interface of a NiMH battery has been modelled using a Ni-MH battery electrode. The proposed circuit characterizes the processes occurring at the hydride electrode interface. For both grinding times, the values of the diffusion coefficients of hydrogen in α phase (10% state of charge) are greater than those found in β phase (100% state of charge). A few possible causes could be lower number of vacant sites available for hydrogen absorption in beta than in alpha phase as well as more significant H-H repulsion, increasing potential barriers or making some diffusion paths improbable.