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About the mechanism and the rate limiting step of the metalhydride electrode reaction

Journal of Alloys and Compounds
Publication Date
DOI: 10.1016/s0925-8388(99)00427-2
  • Metalhydride
  • Ab5
  • Kinetics
  • Electrochemistry
  • Reaction Resistance
  • Chemistry


Abstract LaNi 5 alloy powder samples absorb in the gas phase 80% of their maximum hydrogen capacity (H/M=6) in less than 30 seconds. In the electrochemical discharge process, the charge transfer at the surface of the negative electrode should be the rate determining step because an electrochemical discharge reaction is about an order of magnitude slower than a gas phase desorption process. In this study the alloy system Lm(Ni 3.6Co 0.7Al 0.3Mn 0.4) α with 0.96≤ α≤1.12 was examined as a model system. The reaction resistance of the electrodes was directly measured by means of impedance spectroscopy as a function of the hydrogen concentration in the metalhydride. The high rate dischargeability as well as the resistance are related to the surface composition and surface morphology. The surface composition of a metalhydride electrode not only varies with the cycle number but also changes within a single cycle.

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