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

Zr_0.9−xTi_0.4+xV_1.7(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 ZrV₂decreases but the unit cell volume of ZrV₂increases 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 Zr_0.8Ti_0.5V_1.7reaches 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 Zr_0.8Ti_0.5V_1.7based hydride is related to its larger unit cell volume and higher α-Zr content as compared to Zr_0.9Ti_0.4V_1.7.