Effect of MWCNTs on hydrogen storage properties of a Zr-based Laves phase alloy

In this work, Zr(V_0.95Ni_0.05)₂/MWCNTs composites were prepared by high energy ball-milling under the protection of Ar atmosphere starting with homogeneously annealed Zr(V_0.95Ni_0.05)₂ alloy and MWCNTs. The results show that the as-milled Zr(V_0.95Ni_0.05)₂ alloys with different concentration MWCNTs preserve a ZrV₂ phase with C15 type structure and the lattice parameter of ZrV₂ phase increases with increase of the MWCNTs concentration. During the hydrogenation process, it takes 35, 10, 14, 10 s to reach the 90% of their maximum hydrogen storage capacity at 773 K for the MWCNTs concentration is 1, 2, 5 and 10 wt.%, respectively. It is believed the addition of MWCNTs increase the hydrogenation kinetics in the way of the remarkably increased diffusion rate of H-atoms originating from MWCNTs with hollow structure. In addition, the activation property of Zr(V_0.95Ni_0.05)₂ alloy is not affected significantly by the addition of MWCNTs. The slope of plateau decreases and the width of plateau increases with increasing MWCNTs concentration, which accounts for the increase of the reversible hydrogen storage capacity. In addition, the equilibrium pressure of Zr(V_0.95Ni_0.05)₂ increases with the increase of MWCNTs concentration. The absolute value of enthalpy and entropy decrease as the MWCNTs concentration increase from 1 to 10 wt.%, indicating that the addition of MWCNTs dramatically decreases the stability of Zr(V_0.95Ni_0.05)₂.