Electrochemical hydrogenation of Tb2Ni17-xMx (M = Mg, Sn) phases

The electrochemical hydrogenation of Tb2Ni17-xMx 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 TbNi17-xSnx and x = 0-1.5 for TbNi17-xMgx. 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 Tb2Ni17-xMgx 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 Tb2Ni17-xMx were stable in the electrolyte during the electrochemical processes, i.e. the qualitative and quantitative composition of the observed phases remained unchanged.