Electrochemical Properties and Dissolution Mechanism of A2Ni7 Hydrides (A=Y, Gd, La–Sm)

Abstract The electrochemical behavior of hydride‐forming A 2 B 7 alloys (Y 2 Ni 7 , LaSmNi 7 , and Gd 2 Ni 7 ) 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 Y 2 Ni 7 is mainly sensitive to calendar corrosion and decrepitation, whereas LaSmNi 7 and Gd 2 Ni 7 are sensitive to the concomitant effect of both cycling and calendar corrosion. It is also shown that the capacity loss of Gd 2 Ni 7 can be ascribed to amorphization on cycling, which is not the case for Y 2 Ni 7 . 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.