| AB5-type hydrogen storage alloys have been widely used as active material of the negative electrode in Ni-MH battery because of their excellent performance and relatively low cost. Although many improvements have been obtained for the property of this type of alloys, much more is still needed. In the present paper, electrochemical behavior of AB5-type hydrogen storage alloys has been systematically studied from both fundamental and application aspects.Based on intensive understanding underlying principles of various electrochemical techniques reported in literatures for determination of hydrogen diffusion coefficient in hydrogen storage alloys, these methods have been compared and discussed in theory and practicality, through determining hydrogen diffusion coefficient in the hydrogen storage alloy MlNi3.75Co0.65,Mn0.4A.l0.2 with them. In this study, it was found that, the method proposed by professor White and Dr. Haran (University of South Carolina, USA) for determining hydrogen diffusion coefficient in hydrogen storage alloys, that is based on the transition region of diffusion impedance in Nyquist plot, was seriously imperfect, many values of hydrogen diffusion coefficient differing from each other by 2~5 orders could be obtained with it from a single electrochemical impedance spectroscopy. Then, this technique was modified in this paper and was proved to be correct and applicable.Electrochemical charge transfer and hydrogen transport kinetic performance of hydrogen storage alloy MlNij^jCoo^Mn^Alo^ have been systematically studied in the temperature range from -20癈 to 85 癈. The results showed that the electrode reaction becomes more reversible and gets faster with increase of temperature, and hydrogen diffuses faster at higher temperatures. The activation energy for charge-transfer and for hydrogen diffusion in the alloy with 50%DOD were calculated to be 28.1kJ -mol"1 and in the range of 19.87~20.59kJ ?mol'1 respectively.Effects of particle size in the range from 25.5um to 154.7um on theStudy on electrochemical behavior of AB5-type hydrogen storage alloys for Ni-MH batteryelectrochemical performance of hydrogen storage alloy MlNi3 75Co0 ^Mn,, 4A10 2 have been systematically investigated. It showed that, the smaller is the particle size, the larger is the first discharge capacity and the earlier the saturation capacity is reached. However, the saturation capacity increases with the increase in particle size. The higher is the discharge current, the more obviously the particle size affects the property of the alloy. The effect of particle size on the performance of the alloy changes with the change of measuring temperature. The more uniform is the alloy particle size, the higher is the discharge capacity. The alloy obtained by mixing large particles and small particles has a smaller discharge capacity than that of the large particles, which increases with the content of large particles. However, the relationship between the discharge capacity of the mixture and that of the small particles is much more complicated. The discharge capacity of the mixture decays faster than that of the large particles and that of the small particles.The effects of rare earth composition on the microstructure, thermodynamic performance, electrochemical and kinetic property of AB5-type hydrogen storage alloys Laog(1.x)Ceogx(PrNd)02B5 (B5= Ni355Co075Mn04Al03) have been systematically studied. XRD patterns showed that, though cell parameters and cell volume of the alloy change slightly with the change in the value of x, the microstructure of all the alloys always showed a single phase of CaCu5. With the increase of Ce content in the alloy, equilibrium pressure of hydrogen absorption or desorption increases obviously, hydrogen absorption capacity decreases, and the hydride of the alloy gets unstable. Ce content does not affect activation of the alloy. Discharge capacity of the alloy decreases with the increase in Ce content, however, its charge-discharge voltage plateau becomes higher and i...
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