Electrochemical hydrogenation of Tb₂Ni_17-xM_x (M = Mg, Sn) phases

Chem. Met. Alloys 9 (2016) 153-157

https://doi.org/10.30970/cma9.0346

Vasyl KORDAN, Oksana ZELINSKA, Volodymyr PAVLYUK, Vitaliy NYTKA, Roman SERKIZ

The electrochemical hydrogenation of Tb₂Ni_17-xM_x phases (M = Mg, Sn) was studied for the first time. Both compounds have the hexagonal Th₂Ni₁₇-type structure and small homogeneity ranges, x = 0-1 for TbNi_17-xSn_x and x = 0-1.5 for TbNi_17-xMg_x. Under the conditions of the experiment pure Tb₂Ni₁₇ absorbed approximately 0.55 H/f.u. The Mg-containing phase absorbed approximately 1.14 H/f.u. and the Sn-containing phase ~0.63 H/f.u. In all cases intercalation of hydrogen occurred in octahedral voids 6h of the initial structures, so the coordination polyhedron of the H-atom is an octahedron [HTb₂M₄]. The Tb₂Ni_17-xMg_x phase absorbed the largest amount of hydrogen because magnesium, like rare-earth and transition metals, is able to absorb hydrogen and a combination of these elements leads to better hydrogen absorption. Electron microprobe analysis showed that the electrodes on the basis of Tb₂Ni_17-xM_x were stable in the electrolyte during the electrochemical processes, i.e. the qualitative and quantitative composition of the observed phases remained unchanged.

Unit cell of Tb₂Ni_17-xM_xH_y (y < 3) hydrides and coordination polyhedron of the H-atom.

Keywords

Intermetallic compound / Ni-MH battery / Electrochemical hydrogenation