In this study, we investigate the effect of small amounts of zirconium alloying the medium-entropy alloy (TiVNb)₈₅Cr₁₅, a promising material for hydrogen storage. Alloys with 1, 4, and 7 at.% of Zr were prepared by arc melting and found to be multiphase, comprising at least three phases, indicating that Zr addition does not stabilize a single-phase solid solution. The dominant BCC phase (HEA₁) is the primary hydrogen absorber, while the minor phases HEA₂ and HEA₃ play a crucial role in hydrogen absorption/desorption. Among the studied alloys, Zr4 (TiVNb)₈₁Cr₁₅Zr₄ shows the highest hydrogen storage capacity, ease of activation, and reversibly retrievable hydrogen. This alloy can absorb hydrogen at room temperature without additional processing, with a reversible capacity of up to 0.74 wt.%, corresponding to hydrogen-to-metal ratio H/M = 0.46. The study emphasizes the significant role of minor elemental additions in alloy properties, stressing the importance of tailored compositions for hydrogen storage applications. It suggests a direction for further research in metal hydride alloys for effective and safe hydrogen storage.

TiVNbZrCr high-entropy intermetallic alloy was investigated as a deuterium storage material using gravimetric sorption measurements, thermogravimetric analysis, and temperature-resolved synchrotron X-ray diffraction during deuterium desorption. The as-prepared alloy had an experimentally determined composition of Ti₁₇V₁₉Zr₁₉Nb₂₂Cr₂₃ and a density of 6.59 g·cm⁻³. Empirical alloy-design parameters indicate that the alloy is not a single-phase bcc solid solution, but rather a compositionally complex intermetallic alloy. The calculated hydrogen-affinity descriptors suggest a strong thermodynamic driving force for deuteride formation. Under 5 MPa D₂, the alloy absorbed 3.28 wt.% D, corresponding to D/M = 1.1. After ex situ deuteration, additional diffraction reflections were indexed using tetragonal deuteride reference structures corresponding to ZrV₂D_2.35 and TiD₂, while the Cr-rich bcc phase remained comparatively stable. Thermal desorption released 2.28 wt.% D up to 600 °C in three partially overlapping steps. These results demonstrate that deuterium storage in TiVNbZrCr is governed by phase-selective deuteride formation and decomposition rather than by homogeneous bcc lattice expansion.

Medium-entropy alloys (MEAs) represent a promising class of materials for solid-state hydrogen storage due to their high hydrogen affinity, structural stability, and tunable properties. In this work, a compositional series of (TiZrNbTa)_{100−x}Al_x (x = 0–10 at. %) MEAs were prepared and systematically investigated to clarify the influence of aluminum addition on microstructure, mechanical response, and hydrogen sorption behavior. The alloys were synthesized by arc melting, homogenized by annealing, and characterized using microscopy, X-ray diffraction, density measurements, microhardness testing, nanoindentation, and hydrogen absorption/desorption experiments. Hydrogen sorption was evaluated by isobaric absorption measurements at 2 MPa H₂ over two consecutive cycles, complemented by thermogravimetric desorption analysis of hydrogenated samples. The results show that aluminum addition significantly affects activation behavior, hydrogen uptake, and residual hydrogen retention, while simultaneously increasing hardness and elastic modulus in a non-linear manner. The alloy containing 5 at. % Al exhibits the most balanced performance, combining reduced activation temperature in the second absorption cycle, relatively high hydrogen capacity, and moderate mechanical stiffness. These findings demonstrate that controlled aluminum alloying is an effective strategy for tailoring hydrogen–metal interactions and optimizing the performance of TiZrNbTa-based MEAs for solid-state hydrogen storage applications.