Activation-Free Hydrogen Storage in a Nanostructured TiVCrMn Medium-Entropy Alloy Processed by High-Pressure Torsion

High and medium-entropy alloys are promising candidates for solid-state hydrogen storage; however, their practical implementation remains constrained by demanding activation procedures, limited understanding of long-term cyclic stability, and the necessity for precise microstructural optimization to ensure favorable hydrogen sorption kinetics and reversible storage performance. This study evaluates the effect of microstructure on the hydrogen storage performance of a quaternary, medium-entropy TiVCrMn alloy under moderate pressure and temperature conditions.

Calphad simulations predict a dual-phase BCC + C14 Laves phase microstructure for TiVCrMn below 800 °C. The alloy was produced by arc-melting and characterized by XRD, SEM-EDS, and STEM-EDS, confirming the predicted phase constitution. Disks cut from the as-cast ingot were processed by high-pressure torsion, HPT (5 GPa, 1 rpm, 10 turns), leading to ultrafine microstructures with crystallite sizes of 20-50 nm.

Hydrogenation experiments demonstrated that the HPT process improved the resistance to deactivation. The HPT-processed medium-entropy alloy absorbed 1.6 wt.% hydrogen at 45 °C without requiring any prior activation treatment, exhibiting rapid kinetics (~50 min to reach saturation) and full reversibility in two stages: one at room temperature and the other at 300 °C.

The results indicate that hydrogen absorption occurs predominantly in the BCC phase and that nanostructuring via severe plastic deformation enhances hydrogen uptake and stability against deactivation, highlighting its potential to tailor medium-entropy alloys for hydrogen storage applications.