STUDIES OF HYDROGEN ABSORBING REACTION FOR MH ALLOYS USING THE AC-IMPEDANCE METHOD

The change in the hydrogen absorbing reaction for various hydrogen abs orbing alloys at different charging depths has been investigated using the AC impedance method. The obtained Nyquist plots for LaNi5 showed two semicircles. The small semicircle in the high frequency region sli ghtly changed with increasing charging depth. However, the large semic ircle in the low frequency region decreased at the depth of around 60% . The Nyquist plots were analyzed using the equivalent circuits that a re based on the electrochemical reaction model, and then the component s of the circuits were studied. According to the curve fitting results , it was found that the hydrogen absorbing reaction of LaNi5 changes a t a depth of around 60% to the competition reaction of hydrogen absorb ing and hydrogen gas formation. The impedance of LaNi4.7Al0.3 and LaNi 4.7Co0.3 were also measured. Based on a comparison of these parameters , it was found that the hydrogen absorbing reaction was strongly affec ted by the Ni cluster and the diffusion of hydrogen atoms from the sur face to the inside of the alloy.