Structural Properties of (Ti, Zr)(Mn, Cr)2M0.1 (M = None, Fe, Co, Ni, and Cu) Hydrogen Storage Alloys: Composition Distribution and Occupied Site of Doped Element

CO2 tolerance of hydrogen storage alloys of AB(2)-type (C14 Laves phase) Ti0.515Zr0.485Mn1.2Cr0.8M0.1 (AB(2)-M, M = none, Fe, Co, Ni, and Cu) depends on dopant M. Since our goal is to clarify this mechanism, we determined the elemental analysis using X-ray absorption spectroscopy (XAS), scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and neutron powder diffraction (NPD) with Rietveld refinement in this study. As a result of XAS analysis, a strong evidence of all doped elements occupying B site in AB(2) was obtained. SEM-EDX showed inhomogeneous composition with vacancy in B site and linear correlation of Ti/Zr and Mn/Cr ratio. The peak width in XRD patterns of AB(2)-M depends on the magnitude of homogeneity, therefore the Rietveld analysis using NPD patterns could not be well refined. Thus, homogeneity is not important but element of B site would be important for CO2 tolerance as well as AB(5) type alloys.

Automated summary

This study used multiple analytical methods to reveal the relationship between CO2 tolerance of AB(2)-type hydrogen storage alloys and dopant M, with a focus on the importance of B site elements.