Activation and de/ hydriding behavior in Ti23V40Mn37 alloy by Hf and Hf/Cr substitutions

To improve absorption/desoprtion rate and hydrogen desorption capacity of Ti–V–Mn alloy, Ti23V40Mn37 alloys by Hf and Hf/Cr substitutions were prepared, the activation and hydriding/dehydriding behaviors of the alloys are investigated. Results show that the lattice parameter of BCC phase increases and the ratio of C14 Laves phase also increases by the substitutions. Ti19Hf4V40Mn35Cr2 alloy exhibits the rapid absorption/desoprtion rate and the highest hydrogen desorption capacity of 1.58 wt% H2 at 293 K. The Hydrogenation kinetic mechanism of the alloys is transformed from nucleation-growth to diffusion, and the dehydrogenation kinetic mechanism is only nucleation-growth. The activation energy of Hf/Cr substituted alloy is lower than that of Hf-free alloy, with the values of 53.79 kJ mol−1 H2 and 90.13 kJ mol−1 H2 respectively, which is accounted for the easily absorption of hydrogen molecules on the particle surface and the rapid H diffusion of the interior of alloy, thus the substituted alloys have rapid absorption/desoprtion rate.