Electrochemical hydrogenation of the R₂Zn_17-xMn_x phases (R = Y, La, Gd, Tb)

Chem. Met. Alloys 13 (2020) 78-84

https://doi.org/10.30970/cma13.0409

Nataliya Chorna, Vasyl KORDAN, Vitalii Nytka, Oksana Zelinska, Ivan TARASIUK, Anatoliy Zelinskiy, Volodymyr PAVLYUK

The electrochemical hydrogenation of the solid solutions R₂Zn_17-xMn_x, x = 0.5-0.9 (R = Y, La, Gd, Tb) was studied in Ni-MH battery prototypes for the first time. Phase analysis of the electrode materials on the basis of these compounds was carried out before and after hydrogenation by X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy. All the majority phases crystallize in the hexagonal Th₂Ni₁₇-type structure. As electrodes the alloys showed similar electrochemical behavior and the amount of deintercalated hydrogen increased in the order La < Y < Gd < Tb. The largest degree of amorphization and formation of oxides, such as ZnO and R₂O₃, were observed for the Y- and La-containing alloys after 50 cycles of hydrogenation/dehydrogenation. The geometrically most advantageous sites are octahedral voids in Wyckoff position 6h of the initial structures with a coordination polyhedron [HR₂(Zn,Mn)₄] for the H-atom.

Selected discharge curves for the battery prototypes based on R₂Zn_17-xMn_x.

Keywords

Solid solution / Th₂Ni₁₇-type structure / Electrochemical hydrogenation / Ni-MH battery