Hydrogen is often presented as a clean fuel of the future, but its progress has been constrained by a familiar problem: storage. High-entropy alloys might be the solution.
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Compressing hydrogen demands high pressures; liquefying it requires extreme cooling. Both approaches carry energy penalties, safety considerations, and infrastructure costs that limit wider adoption.
An alternative is to store hydrogen within solid materials rather than in tanks. Metal hydrides have long offered this possibility, combining intrinsic safety with high volumetric density.
More recently, attention has turned to high-entropy alloys - materials built from multiple principal elements that form unusually stable solid solutions.1,2
Their chemical disorder, once seen as a drawback, may in fact be their advantage. For hydrogen storage, it shapes how hydrogen enters, moves through, and exits the lattice, as well as how the material endures repeated cycling.
This article explores how high-entropy alloys work, why they matter for hydrogen storage, and what remains to be solved before they can move beyond the laboratory.
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What Are High-Entropy Alloys?
High-entropy alloys differ from traditional alloys in that they must be composed of five or more principal elements, each typically present in concentrations ranging from five to 35 atomic percent.
The combination of multiple principal elements results in a high configurational entropy of mixing (ΔSmix), which favors the formation of simple solid-solution phases, such as body-centered cubic (BCC), face-centered cubic (FCC), or Laves structures, rather than complex and brittle intermetallic compounds.
While configurational entropy plays a key role, lattice strain, electronic effects, and enthalpy contributions also influence phase stability in practical HEA systems. The term “high-entropy alloy” originates from this exceptionally high configurational entropy, which is a measure of chemical disorder.3
This entropy-stabilized disorder produces a uniform yet flexible crystal lattice that can accommodate atoms with different sizes and bonding characteristics, thereby facilitating efficient hydrogen incorporation.
Collectively, these structural attributes give rise to the four fundamental effects that govern the distinctive hydrogen storage behavior of high-entropy alloys.3
Fundamental Features of HEAs for Hydrogen Storage
High-entropy alloys exhibit a combination of structural and kinetic characteristics that are well-suited to solid-state hydrogen storage. Together, these features help explain why HEAs often outperform more conventional alloys and metal hydrides.
Structural Stability Through High Entropy
The presence of multiple principal elements increases the configurational entropy of the system, stabilizing simple solid solution phases such as BCC or related lattices.
This stability suppresses the formation of brittle intermetallic compounds that can block hydrogen diffusion. A stable solid solution provides a larger number of accessible interstitial sites for hydrogen atoms to reside, improving hydrogen uptake without degrading the structure.
Lattice Distortion Enhances Hydrogen Accommodation
Because the constituent elements have different atomic sizes (for example, Ti, V, Zr, Nb, and Hf), the crystal lattice of high-entropy alloys becomes severely distorted.
This distortion expands and modifies the local interstitial potential landscape, making it easier for hydrogen atoms to enter the lattice at lower temperature and pressure compared to more ordered alloys.
The increase in available sites and reduced energy barriers directly contributes to improved hydrogen capacity and faster uptake.
Retained Microstructure Via Sluggish Diffusion
In high-entropy alloys, chemical complexity and diverse local atomic environments can suppress rapid diffusion and microstructural coarsening. This sluggish diffusion helps to preserve a fine and stable microstructure even after many hydrogen absorption and desorption cycles.
A stable microstructure with abundant grain boundaries enhances hydrogen transport and reduces degradation over time.
Synergistic “Cocktail” Effect
The individual characteristics of each element in a high-entropy alloy contribute to the overall behavior of the material.
For example, Zr and Ti contribute to high hydrogen capacity, V enhances hydrogen affinity, while Fe reduces overall cost. In combination, these elements can offer hydrogen storage performance that exceeds expectations based on the simple average of individual element properties.
Selecting the composition of HEAs for hydrogen storage requires balancing element size, electronegativity, valence electron concentration, and hydride-forming ability.
Traditionally, compositions were chosen through trial and error, but modern approaches, such as CALPHAD thermodynamic modeling, density-functional theory (DFT), and machine-learning-based predictive algorithms, now enable the rapid screening of multi-element combinations.
These tools help to identify stable solid-solution regions, predict H-solubility and lattice distortion, and significantly reduce experimental time, cost, and material waste.
Scientific Highlights
Scientific studies highlight several high-entropy alloys with promising hydrogen storage capabilities.
A BCC HEA with elements V-Nb-Cr-Mo-Mn was found to store 2.83 wt.% H2 at room temperature and ambient pressure. This is higher than benchmark metal hydrides such as LaNi5H6 (1.38 wt.%) and TiFeH2 (1.91 wt.%).4
High-entropy alloy Ti-V-Zr-Cr-Mn-Fe-Ni, with its dual BCC + Laves structure, shows ~1.6 wt.% hydrogen uptake with full reversibility and easy activation.
These results reveal that selected HEAs can achieve higher hydrogen storage capacities compared with benchmark intermetallic hydrides while offering improved structural stability and compositional flexibility.
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Current Challenges
High-entropy alloys such as Ti-V-Zr-Nb-Hf, Ti-V-Nb-Cr, and Ti-V-Zr-Nb show promising hydrogen uptake but face practical limitations. Ti-V-Zr-Nb-Hf stores about 1-2 wt.% hydrogen, limiting energy density for mobile applications, while Ti-V-Nb-Cr releases hydrogen only at high temperature, slowing system response.
Alloys containing Zr or Hf often develop lattice strain and elemental segregation after repeated cycling, reducing long-term stability. Several V-rich alloys require extended high-temperature activation to reach full capacity, increasing energy cost.
Production is also challenging and expensive due to the use of refractory metals and complex melting processes.
Together, these limitations point to the need for better control over composition, activation, and long-term cycling before high-entropy alloys can be considered for practical hydrogen storage.
What Needs to Be Done for HEAs to Make a Real Impact
To move HEA-based hydrogen storage from lab-scale curiosity to practical systems, the following directions are critical:
Optimization via Design Tools: Use computational methods (CALPHAD, machine learning) to narrow down promising compositions. This approach reduces trial-and-error synthesis, focusing experimental work on high-potential candidates.
Improving Kinetics and Reversibility at Ambient Conditions: Develop HEAs that can absorb/desorb hydrogen near room temperature and ambient pressure, with fast kinetics and minimal activation requirements.
Recent AB-type HEAs showing reversible hydrogen storage of ~1.6 wt.% at room temperature demonstrate encouraging progress.
Lightweight & Cost-Effective Compositions: A shift toward lighter element combinations (e.g., including Al and light transition metals) will improve gravimetric density, lower costs, and make production more feasible.
System-Level Integration and Engineering: Beyond materials development, integration of HEAs into practical storage systems like tanks, hydride beds, and heat management must be addressed.
Engineering studies, life-cycle assessments, and safety evaluations will also be essential.
Long-Term Cycling & Degradation Studies: Perform extended cycling tests under realistic conditions to evaluate mechanical stability, hydrogen capacity retention, and safety over hundreds to thousands of cycles.
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Time Will Tell for High-Entropy Alloys
High-entropy alloys are unlikely to offer a simple or immediate answer to hydrogen storage, but they have already shifted how the problem is being approached.
By expanding the design space beyond conventional alloys, they invite new ways of thinking about stability, reversibility, and performance.
Whether this promise translates into practical systems will depend on their careful design, engineering, and long-term validation.
References and Further Reading
- Schlapbach, L. and A. Züttel, Hydrogen-storage materials for mobile applications. Nature, 2001. 414(6861): p. 353-358.
- 2. Marques, F., et al., Review and outlook on high-entropy alloys for hydrogen storage. Energy & Environmental Science, 2021. 14(10): p. 5191-5227.
- Sahlberg, M., et al., Superior hydrogen storage in high entropy alloys. Scientific Reports, 2016. 6(1): p. 36770.
- Qiu, G., et al., High entropy powering green energy: hydrogen, batteries, electronics, and catalysis. npj Computational Materials, 2025. 11(1): p. 145.
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