Influence of the alloy morphology on the kinetics of AB(5)-type metal hydride electrodes

Three different cast LmNi(3.6)Co(0.7)Al(0.3)Mn(0.4) alloys (Lm=Lanthanum ri ch mischmetal) were used for the investigation. One alloy was rapidly coole d, 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 al loys, measured by means of Electrochemical Impedance Spectroscopy (EIS) and electrochemical charge discharge experiments. The rapidly cooled alloy sam ple showed better fast discharge behavior and smaller reaction resistance c ompared to annealed samples. In combination with X-ray diffraction (XRD) an d Scanning Electron Microscopy (SEM) a possible explanation on the improved kinetics of the rapidly cooled electrode can be given: The smaller grain s ize and the high amount of grain boundary in the alloy leads to a faster ac tivation and therefore to an enhanced alloy surface. This results in a smal ler reaction resistance and an improved fast discharge behavior. (C) 1999 E lsevier Science S.A. All rights reserved.