Electrochemical hydrogenation of solid solutions based on the intermetallic compound SmNi5

 

Chem. Met. Alloys 12 (2019) 77-87

https://doi.org/10.30970/cma12.0396

 

Vasyl KORDAN, Ivan TARASIUK, Iryna STETSKIV, Roman SERKIZ, Volodymyr PAVLYUK

 

The electrochemical hydrogenation of SmNi5-xMx phases (M = In; In+Sn) and the binary compound SmNi5 has been studied for the first time by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy. All these phases crystallize in hexagonal CaCu5-type structures. The solubility of In or In+Sn in the binary compound SmNi5 is not higher than 5.0-5.5 at.%, which can be explained by the large difference between the atomic radii of the doping components (In, Sn) and nickel. At charging to the 3 H/f.u. level (current density 1.0 mA/cm2) the electrodes based on the binary, ternary and quaternary phases demonstrated maxima of 2.41, 2.52, and 2.72 H/f.u., respectively. The most geometrically advantageous sites in the initial structures are octahedral voids (Wyckoff position 3f), where the coordination polyhedron of the H-atom is an octahedron of composition [HSm2M4]. The results of the spectral analysis showed that the In-doped electrode lost In in specific interactions of the surface with the electrolyte during the electrochemical process, in contrast to the other electrodes, which are stable (the qualitative and quantitative compositions of the observed phases remained unchanged).

 

 

Unit cell of RM5 hydrides and coordination polyhedra of the H-atoms.

 

Keywords

X-ray diffraction / Electron microscopy / Solid solutions / CaCu5-type structure / Ni-MH battery / Electrochemical hydrogenation