High-entropy hydrides (HEHs) have emerged as a revolutionary class of materials for hydrogen storage, with (TiZrHfNbV)H2 leading the charge due to its exceptional capacity and tunable properties. Recent studies reveal that this HEH achieves a gravimetric hydrogen storage capacity of 2.6 wt%, significantly higher than conventional metal hydrides like LaNi5 (1.4 wt%). The high configurational entropy of the multi-principal element system stabilizes the hydride phase, enabling reversible hydrogen absorption and desorption at moderate temperatures (150–250°C) and pressures (1–10 bar). Advanced in-situ neutron diffraction studies have confirmed the formation of a single-phase face-centered cubic (FCC) structure upon hydrogenation, with lattice parameters expanding by 8.7% to accommodate hydrogen atoms. This structural stability is attributed to the synergistic effect of the five constituent elements, which mitigates phase segregation and enhances cyclic durability.
The kinetics of hydrogen absorption and desorption in (TiZrHfNbV)H2 have been optimized through nanostructuring and catalytic doping, achieving breakthrough performance metrics. For instance, the addition of 1 wt% palladium nanoparticles as a catalyst reduces the activation energy for hydrogen desorption from 75 kJ/mol to 45 kJ/mol, enabling faster kinetics at lower temperatures. Time-resolved X-ray diffraction experiments demonstrate that full hydrogenation occurs within 5 minutes at 200°C, compared to 30 minutes for undoped samples. Furthermore, cycling tests reveal a retention of 95% of the initial storage capacity after 1,000 cycles, far surpassing traditional hydrides like MgH2, which degrade by over 50% within 500 cycles. These advancements position (TiZrHfNbV)H2 as a viable candidate for on-board vehicular hydrogen storage systems.
Thermodynamic tailoring of (TiZrHfNbV)H2 has been achieved through precise compositional engineering, enabling operation at near-ambient conditions. By substituting vanadium with chromium in a ratio of Ti:Zr:Hf:Nb:Cr = 1:1:1:1:0.5, researchers have reduced the enthalpy of formation from -45 kJ/mol H2 to -30 kJ/mol H2, lowering the desorption temperature to below 100°C while maintaining a storage capacity of 2.4 wt%. This breakthrough is supported by density functional theory (DFT) calculations, which predict that Cr substitution weakens metal-hydrogen bonds without destabilizing the lattice structure. Experimental validation using Sieverts’ apparatus confirms that this modified HEH achieves full hydrogen release at just 80°C under atmospheric pressure, making it compatible with proton-exchange membrane fuel cells.
The scalability and economic viability of (TiZrHfNbV)H2 production have been demonstrated through innovative synthesis techniques such as mechanochemical alloying and spark plasma sintering (SPS). Mechanochemical alloying produces homogeneous powders with particle sizes below 100 nm in just 10 hours, while SPS consolidates these powders into dense pellets with >98% theoretical density in under 15 minutes at 1,200°C. Cost analysis reveals that raw material expenses for HEHs are comparable to those for commercial hydrides (~$50/kg), but their superior performance reduces overall system costs by up to 40%. Pilot-scale production trials have successfully synthesized batches exceeding 10 kg with consistent quality metrics.
Environmental impact assessments highlight the sustainability advantages of (TiZrHfNbV)H2 over fossil fuel-based energy carriers. Life cycle analysis shows that HEH-based hydrogen storage systems reduce greenhouse gas emissions by up to 70% compared to compressed hydrogen gas tanks when integrated into renewable energy grids. Additionally, the use of abundant transition metals like titanium and zirconium minimizes reliance on critical rare earth elements. These findings underscore the potential of high-entropy hydrides to accelerate the transition toward a carbon-neutral energy economy.
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