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

• Published in: ChemElectroChem Vol. 2; no. 9; pp. 1321 - 1330
• Main Authors: Puga, Beatriz, Joiret, Suzanne, Vivier, Vincent, Charbonnier, Véronique, Guerrouj, Habiba, Zhang, Junxian, Monnier, Judith, Fariaut‐Georges, Cécile, Latroche, Michel, Goubault, Lionel, Bernard, Patrick
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 01.09.2015; John Wiley & Sons, Inc
• Subjects: alloys; batteries; Dissolution; electrochemical impedance spectroscopy; hydrides; rare earth metals; Spectrum analysis
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.201500163

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. Corrosion calendar: The electrochemical behavior of hydride‐forming A2B7 alloys such as Y2Ni7 is investigated in KOH solution by using electrochemical impedance spectroscopy, SEM, XRD, and Raman spectroscopy. This showed that Y2Ni7 undergoes calendar corrosion and decrepitation with formation of needle‐shaped corrosion products and grain cracking (see picture).