Liquid hydrogen (LH₂) is attractive for long-distance energy transport because of its high volumetric energy density. But even well-insulated tanks cannot completely prevent heat from entering. As the liquid warms, hydrogen evaporates and pressure builds, leading to boil-off losses during storage and transport.

A research team, led by Professor Hyunchul Oh of the Department of Chemistry at UNIST, together with Professor Hoi Ri Moon of Ewha Womans University, and researchers at the Technical University of Munich in Germany, has investigated whether porous materials could help limit these losses. The team used metal-organic frameworks (MOFs)—highly porous crystalline materials—to capture evaporating hydrogen and delay its release as heat enters the tank.

MOFs contain networks of nanoscale pores that can absorb hydrogen onto their internal surfaces. At cryogenic temperatures, interactions between hydrogen molecules and the pore walls help keep the gas confined, slowing pressure buildup. The approach complements conventional insulation—instead of focusing only on limiting heat entering the tank, it also changes how hydrogen responds once heat gets in.

The key question is whether that benefit comes at the expense of storage capacity. A porous material takes up space that would otherwise hold liquid hydrogen. The researchers therefore compared two MOFs with very different structures—IRMOF-20, a rigid framework with a large pore volume, and MIL-53(AI), a flexible framework whose pores expand and contract as hydrogen is adsorbed.

IRMOF-20 offers a particularly favorable balance. When the researchers accounted for the space occupied by the material, the system retained about 97% of the volumetric capacity of neat liquid hydrogen. This was possible because hydrogen confined within the pores packed densely enough to compensate for much of the space taken by the MOF.

The researchers then modeled how the materials would affect boil-off in a transport-scale liquid hydrogen tank. Under the mid-vacuum insulation conditions examine, neat liquid hydrogen was predicted to deplete after about 64 days. With IRMOF-20, that period increased to approximately 221 days—more than three times as long.

Experiments offered clues to why IRMOF-20 performed this way. Adsorption measurements indicated that hydrogen confined within its pores reached an effective density higher than that of bulk liquid hydrogen. Inelastic neutron scattering also showed restricted molecular rotation inside the pores, providing indirect evidence of strong interactions between hydrogen and the framework. Together, the results suggest that nanoscale confinement can both pack hydrogen dedensely and stabilizze it against release as temeprature rises.

MIL-53(AI) behaved differently. It retained hydrogen more strongly as temperature increased, but its volumetric capacity was only about 53% of that of liquid hydrogen. The contrast highlights a central design choice for porous materials in cryogenic hydrogen storage—larger pore volume favors capacity, while stronger confinement can improve thermal retention.

“By considering pore volume, hydrogen density, and desorption behavior together, we found that poros materials could reduce boil-off while preserving much of the storage capacity needed for liquid hydrogen transport,” said Professor Oh. “These calculations represent an idealized upper bound, so further work is needed to determine how closely this performance can be reproduced in practical tank systems.”

Jaewoo Park of UNIST served as first author, with contributions from Dr. Monica Jiménez-Ruiz of the Institut Laue-Langevin in France and Dr. Margarita Russina of Helmholtz-Zentrum Berlin fur Materialien und Energie in Germany, among others.

The research was supported by the National Research Lab (NRL 2.0) Program, including the Institute for Multiscale Matter and Systems (IMMS), and the BrainLink program of the National Research Foundation of Korea. The findings were published in Nature Communications on September 7, 2026.