Reduction in reversible hydrogen
storage capacity with increasing
hydrogenation and dehydrogenation cycle number is observed in numerous
hydrogen storage materials, but the mechanism behind this unfavorable
change has not been elucidated yet. In this study, we have investigated
the development of structural defects or disorders in V1–x
Ti
x
H2, x = 0, 0.2, and 0.5, during the first 15 hydrogen absorption
and desorption cycles using the atomic pair distribution function
(PDF) analysis of synchrotron X-ray total scattering data to find
out the possible structural origin of the poor cyclic stability of
V1–x
Ti
x
alloys. While pure vanadium shows no significant change in the PDF,
alloy samples subject to several hydrogenation and dehydrogenation
cycles display fast decaying of the PDF profile due to a progressive
increase in the PDF peak width with increasing r.
This r-dependent PDF peak broadening effect becomes
stronger with cycle number. Molecular dynamics (MD) simulations demonstrated
that dislocation defects explain characteristic features in our experimental
PDFs very well and suggested that a large number of dislocations are
formed during hydrogen cycling. We found there is a close relation
between the reduced amount of the reversible hydrogen content of V0.8Ti0.2 and the amount of generated dislocations.
On the basis of the PDF analysis results, a possible mechanism behind
degradation in the reversible hydrogen storage capacity of V1–x
Ti
x
is discussed.