Relation between Hydrogen Storage Properties and Structure of Nd–Co–B Amorphous Alloys

Abstract

Hydrogen storage properties of Nd x Co 85-x B 15 (x=5-30) amorphous alloys produced by melt-spinning, such as hydrogen absorbing rates, storage capacities and desorption spectra, have been measured and compared with their structural features such as radial distribution functions and coordination numbers obtained by X-ray diffraction analyses. The storage capacity under I MPa H 2 at 423 K increases nearly quadratically with Nd concentration as H/M≅0.001x 2 (M=Nd+Co+B). The absorbed hydrogen is desorbed upon heating in stages around 350-600 K and at higher temperatures. The first stage is desorption from the amorphous phase, and most of the hydrogen is desorbed at this stage in the alloys with x ≤ 20. Hydrogen atoms are accommodated in tetrahedral sites of Nd 2 Co 2 and Nd 3 Co 1 configurations separated from trigonal prisms composed of Co and B atoms, and extend the Nd-Nd pair distance by 9% and Nd-Co by less than 3% but not influencing the Co-Co distance at all. The coordination numbers about Nd and Co atoms are preserved before and after hydrogenation, indicating that the medium- as well as long-range atomic distribution is not modified by hydrogen absorption in these amorphous alloys.