# Designing TiZrNbTa-Al Medium-Entropy Alloy for Next-Generation Hydrogen Storage

## TL;DR

This paper explores how adding aluminum to a specific metal alloy improves hydrogen storage performance by balancing hydrogen uptake and mechanical properties.

## Contribution

The study introduces a new TiZrNbTa-Al medium-entropy alloy optimized for hydrogen storage through controlled aluminum alloying.

## Key findings

- Aluminum addition reduces activation temperature and increases hydrogen capacity in TiZrNbTa-based alloys.
- 5 at. % Al content provides the best balance of hydrogen storage performance and mechanical stiffness.
- Aluminum alloying enhances hardness and elastic modulus in a non-linear manner.

## Abstract

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}Alx (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.