Enhancing TiFe Alloy Activation for Hydrogen Storage Through Al, Cr, Co, and Cu Substitutions as a Step Towards Future Recycling

This study investigates the activation behavior of $TiFe_{0.80}$-$X_{0.20}$ (X = Co, Cu, Cr, Al) alloys to identify the most effective materials for producing hydrogen storage alloys from recycled sources in view of a circular economy perspective. Activation was tested using two methods: a Sievert Volumetric Apparatus at room temperature and 64 bar of hydrogen, and high-pressure differential scanning calorimetry with 50 bar hydrogen under thermal cycles up to 400 {\deg}C. Activation properties were analyzed by assessing time for incubation and for full charging, that are influenced, respectively, by surface and bulk diffusion of hydrogen. Results showed that Cr-substituted alloys are rapidly activated, due to the presence of $TiCr_{2}$ compound, while Al-containing alloys absorbed hydrogen immediately. In contrast, Co- and Cu-substituted alloys required extended activation times, due to less quantity of secondary phases and limited diffusion channels.