Modification of BCC phase and the enhanced reversible hydrogen storage properties of Ti-V-Fe-Mn alloys with varied V/Fe ratios

Ti-V-based alloys are proved of huge potential in storing hydrogen, but the incomplete reversible hydrogen storage capacity caused by overstability of V hydride has limited the large-scale application. In this study, Ti32V40+xFe23-xMn5 (x=0, 4, 8, 12, at.%) alloys were designed, and the effects of V/Fe ratio on phase constitution and hydrogen storage properties were investigated. The main phase of the alloys is body-centered cubic (BCC) phase, and the lattice constants of the BCC phase decrease with the decrease of V/Fe ratio. Moreover, C14 Laves phase exists in alloys with a Fe content of 19at.% to 23at.%. For hydrogenation, the C14 Laves phase can accelerate the hydrogen absorption rate, but the hydrogen absorption capacity is reduced. With the decrease of V/Fe ratio, the hydride gradually destabilizes. Owing to its large lattice constant and high hydrogen absorption phase content, the Ti32V52Fe11Mn5 alloy shows the most enhanced hydrogen storage properties with hydrogenation and dehydrogenation capacities of 3.588wt.% at 298 K and 1.688wt.% at 343 K, respectively. The hydrogen absorption capacity of this alloy can be reserved to 3.574wt.% after 20 cycles of hydrogen absorption and desorption.