Hydrogenation thermokinetics and activation behavior of non-stoichiometric Zr-based Laves alloys with enhanced hydrogen storage capacity

Zr0.9−xTi0.4+xV1.7 (x = 0, 0.1) non-stoichiometric alloys are designed and expected to show improved hydrogen storage capacities of Zr-based Laves phase alloys. The samples are synthesized by arc melting followed by two different processing techniques: annealing and melt-spinning. Phase constituent and microstructure investigations reveal the multiphase structures containing C15-Laves type ZrV2, V- and Zr-based solid solutions for the annealed alloys and melt-spun ribbons. The content of ZrV2 decreases but the unit cell volume of ZrV2 increases with increasing Ti content. Activation behavior and hydrogenation kinetics at different temperatures of the annealed and melt-spun samples were studied. At 25 °C, the hydrogen absorption capacity of Zr0.8Ti0.5V1.7 reaches 2.83 wt% H. The apparent activation energies of the fast hydrogen absorption stage (α, α+β regions) are calculated to be 2-5 kJ/mol. Melt-spun ribbons exhibit higher hydrogen absorption rate and smaller hydrogen storage capacities than the annealed alloys in the initial cycle. The surface and sub-surface chemical compositions are analyzed by XPS to illustrate the influence of composition of the alloys on activation behavior. Hydrogen absorption/desorption PCT curves of the annealed samples between 400 and 550 °C were measured and allowed to derive corresponding thermodynamics parameters. The higher hydride stability of the Zr0.8Ti0.5V1.7 based hydride is related to its larger unit cell volume and higher α-Zr content as compared to Zr0.9Ti0.4V1.7.