An electrochemical study of mono-substituted intermetallic hydrides

The electrochemical behaviour of LaNi2.5Co2.5, LaNi4.5 Mn-0.5 and LaNi4.5Al0.5 intermetallic compounds was investigated using chronopotentiometric and impedance measurements. Electrochemical isotherms have been found to be in good agreement with solid gas determinations. Kinetics data are drawn from impedance spectroscopy for the three compounds. Important changes in the magnitude of a low frequency semicircle in the impedance diagrams have been correlated to a corrosion layer effect which is strongly reduced from the first cycle and as cycling proceeds. A subsequent increase in the apparent hydrogen chemical diffusion coefficient Do is found from the first cycle, which is well correlated to the decrease of the diffusion length through the oxide layer as the thickness of the corrosion layer decreases. The apparent hydrogen chemical diffusion coefficient is found to be one order of magnitude larger in the a phase (10(-10) cm(2)/s) than in the beta phase. (C) 2003 Elsevier B.V. All rights reserved.