Hydrogen-sorption properties of Nb4M0.9Si1.1 (M = Co,Ni) hydrides

• Nb4M0.9Si1.1 (M = Co,Ni) synthesised via high temperature methods.
• Synthesis confirmed using phases analysis using the Rietveld method.
• PCT and TDS of Nb4M0.9Si-Hx shows low equilibrium pressure and slow kinetics.
• Hydrogen sorption properties depend on available sites for H-atoms.

Nb4M0.9Si1.1 (M = Co,Ni) is synthesised using high temperature techniques and its properties characterised using PXRD, PCI and TPD. It is shown that the hydrogen-sorption properties of Nb4M0.9Si1.1 (M = Co,Ni) are dominated by a low equilibrium pressure, low storage capacity and slow kinetics. These properties can in large part be explained by the crystal structure of the materials: kinetics are slow because of the arrangement of available H-sites (which are tetrahedral voids coordinated Nb-atoms) in 1d-“chains” possibly limiting diffusion in the two other dimensions; the high affinity for hydrogen of Nb and the large size of these voids explain the low equilibrium pressure; close proximity of most available H-sites to sites partially occupied by Si explains the low storage capacity.