Electrochemical Properties and Dissolution Mechanism of A2Ni7 Hydrides (A=Y, Gd, La–Sm)
Résumé
The electrochemical behavior of hydride-forming A2B7 alloys
(Y2Ni7, LaSmNi7, and Gd2Ni7) is investigated in KOH solution.
The evolution of the material performance is shown to strongly
depend on the A elements. Electrochemical impedance
spectroscopy (EIS), SEM observations, XRD, and Raman spectroscopy
showed that Y2Ni7 is mainly sensitive to calendar corrosion
and decrepitation, whereas LaSmNi7 and Gd2Ni7 are sensitive
to the concomitant effect of both cycling and calendar corrosion. It is also shown that the capacity loss of Gd2Ni7 can
be ascribed to amorphization on cycling, which is not the case
for Y2Ni7. The formation of both an thin oxide film (a few tens
of nanometers thick) at the material surface, measured by EIS,
and the dissolution products formed during long-term immersion,
analyzed by Raman spectroscopy, is in agreement with
the decrease in material activity evaluated by EIS during cycling
at different depths of charge.