In situ neutron diffraction study of the kinetics of metallic hydride electrodes

Using a new design of electrochemical cell for in situ neutron powder diffraction of electrode material in alkaline media, and taking advantage of the D20 diffractometer at the Laue Langevin Institute (high flux and large position sensitive detector), we were able to follow the structural evolution of LaNi5-type metal hydride electrodes at high charge/discharge rates on surface-treated material characterised by transmission electron microscopy. From the evolution of the relative amounts and the unit cell volumes of the alpha and beta phases at transients, we show that for surface-treated and activated materials, the main rate limitation is the kinetics of the alphadouble left right arrowbeta phase trans formation, i.e. the mobility of the phase interface and not the diffusion coefficient of the hydrogen in the phases (here deuterium, for neutron diffraction reasons). (C) 2002 Elsevier Science B.V. All rights reserved.