High-entropy hydrides (HEHs) represent a paradigm shift in hydrogen storage materials, leveraging the unique properties of multi-principal element systems. Recent studies on (TiZrHfNbV)H2 have demonstrated exceptional hydrogen storage capacities, achieving up to 2.5 wt% at ambient temperatures and pressures as low as 10 bar. This performance is attributed to the synergistic effects of multiple metal elements, which create a complex lattice structure with numerous interstitial sites for hydrogen absorption. Density functional theory (DFT) calculations reveal that the configurational entropy stabilizes the hydride phase, reducing the enthalpy of formation to -45 kJ/mol H2, significantly lower than conventional binary hydrides like MgH2 (-75 kJ/mol H2). The high entropy also mitigates phase segregation, ensuring uniform hydrogen distribution and enhanced cycling stability over 1,000 cycles with less than 5% capacity loss.
The kinetics of hydrogen absorption and desorption in (TiZrHfNbV)H2 are remarkably fast due to the presence of multiple diffusion pathways facilitated by the disordered lattice structure. Experimental data show that at 100°C, the material achieves 90% of its maximum hydrogen capacity within 5 minutes, with a desorption rate of 0.8 wt%/min under vacuum conditions. This is a tenfold improvement compared to traditional hydrides such as LaNi5H6, which typically require over an hour for similar uptake. The activation energy for hydrogen diffusion in HEHs is measured at 0.3 eV, significantly lower than the 0.6 eV observed in binary hydrides. These properties make HEHs ideal for rapid refueling applications in hydrogen-powered vehicles and portable energy systems.
The mechanical properties of high-entropy hydrides further enhance their suitability for practical applications. Nanoindentation tests on (TiZrHfNbV)H2 reveal a hardness of 8 GPa and a Young’s modulus of 180 GPa, comparable to high-strength steels but with superior resistance to embrittlement during repeated hydrogen cycling. This is attributed to the inherent lattice distortion and stress accommodation mechanisms in HEHs, which prevent crack propagation even under extreme pressure conditions (>100 bar). Additionally, thermal expansion measurements indicate a coefficient of thermal expansion (CTE) of 12 ppm/K, ensuring dimensional stability across a wide temperature range (-50°C to 200°C). These mechanical characteristics make HEHs robust candidates for integration into high-pressure storage tanks and fuel cell systems.
The scalability and cost-effectiveness of synthesizing high-entropy hydrides have been validated through advanced manufacturing techniques such as mechanochemical alloying and spark plasma sintering (SPS). Large-scale production trials have achieved yields exceeding 95% with minimal energy consumption (~500 kWh/ton), making HEHs economically competitive with existing storage materials like metal-organic frameworks (MOFs) and complex hydrides. Life cycle assessments indicate that HEHs reduce carbon emissions by up to 30% compared to conventional storage systems due to their lower processing temperatures (<600°C) and reduced reliance on rare earth elements. These advancements position HEHs as a sustainable solution for large-scale hydrogen infrastructure development.
Finally, the tunability of high-entropy hydrides opens new avenues for optimizing performance through compositional engineering. Recent studies have demonstrated that substituting Nb with Ta in (TiZrHfNbV)H2 increases the hydrogen storage capacity to 3 wt% while maintaining excellent kinetics and mechanical properties. Machine learning models trained on experimental datasets predict that further optimization could yield capacities exceeding 4 wt% by fine-tuning elemental ratios and processing parameters. This adaptability allows HEHs to be tailored for specific applications, from grid-scale energy storage to aerospace propulsion systems.
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