H2 storage
What is
H2 storage
and why it is important
Hydrogen is an ideal clean energy source because its sole product after combustion is H2O and no greenhouse gases or environmentally harmful compounds are released. H2 is of particular interests in automotive applications because it is a zero-emission fuel, abundantly available, and, when liquefied, has triple the energy density of gasoline. A full system based on H2 involves its production, delivery, and storage, as well as the fuel cell technology. Among them, H2 storage play a key role in this development.

The inherent volatility of H2 at ambient conditions poses significant challenges for its physical storage in pressurized tanks, which typically offer only modest volumetric energy densities. To enhance the practicality of H2 as a fuel for daily use, there is a pressing need for the development of low-cost, lightweight materials that are capable of reversible hydrogen uptake and storage densities greater than that of liquid hydrogen.
Technologies to store H2
  • Cryogenic
    Storage
    H2 can be liquified at low temperature and high pressure. Liquid hydrogen has been used by NASA to propel space shuttles into orbit and today some vehicles have been running on pressurized hydrogen. However, cryogenic storage of H2 is accompanied by high operational costs and an increased weight of the cryogenic tanks.
  • Chemical Storage Materials
    Chemical storage materials could form chemical bonds with hydrogen, and thus H2 can be stored in a chemical way. Metal hydrides, boranes, or imidazolium ionic liquids have been extensively studied for this purpose. However, since chemical bond association and dissociation are involved in the adsorption and desorption process, this technology usually suffers from slow kinetics. Possible contaminations in H2 would also quickly deactivate the materials, affecting its cyclability.
  • Physical Storage Materials
    Without chemical bond formation, physical storage materials that can effectively adsorb hydrogen at relatively low pressures and under non-extreme temperature conditions. Metal-organic frameworks (MOFs) combine high surface areas, low densities, and facile functionalization, thus allowing for the development of storage materials with high gravimetric and volumetric H2 uptake. However, its storage capacity still needs further improvement.
Future Directions
The US Department of Energy (DOE) 2025 targets for hydrogen storage systems are a gravimetric uptake of 0.055 kg(H2) kg−1 and a volumetric capacity of 0.04 kg(H2) L−1, while retaining short refueling times and high cycling stability at operating temperatures between -40 and 60°C. Scientists are still working on different schemes to meet this target.
With the help of Artificial intelligence, MOF materials with higher H2 adsorption capacity are strong candidates to meet this 2025 target and the long term goal (a gravimetric uptake of 0.065 kg(H2) kg−1 and a volumetric capacity of 0.05 kg(H2) L−1).
What can AI offer:
  • Systematically calculation on the heat of H2 adsorption for MOF materials as a strong indicator for MOF–H2 interaction.
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  • Pore engineering (size, shape, connectivity, and metal sequence and distribution) of the materials for enhanced H2 gravimetric and volumetric density.
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  • Find the best building units and the consequent synthetic route of the new material.
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  • Management of the whole research scheme.
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