Influence of the alloy morphology on the kinetics of AB5-type metal hydride electrodes

Three different cast LmNi(3.6)Co(0.7)Al(0.3)Mn(0.4) alloys (Lm=Lanthanum rich mischmetal) were used for the investigation. One alloy was rapidly cooled, a second was rapidly cooled and annealed and the third one was cast in a conventional way. Our main interest are the kinetic properties of these alloys, measured by means of Electrochemical Impedance Spectroscopy (EIS) and electrochemical charge discharge experiments. The rapidly cooled alloy sample showed better fast discharge behavior and smaller reaction resistance compared to annealed samples. In combination with X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) a possible explanation on the improved kinetics of the rapidly cooled electrode can be given: The smaller grain size and the high amount of grain boundary in the alloy leads to a faster activation and therefore to an enhanced alloy surface. This results in a smaller reaction resistance and an improved fast discharge behavior. (C) 1999 Elsevier Science S.A. All rights reserved.