Researchers at the Ulsan National Institute of Science and Technology (UNIST) have developed a technique to curb liquid hydrogen boil-off losses by filling storage tanks with metal-organic frameworks (MOFs). Published on the 29th in Nature Communications, the study shows this method extends storage duration more than threefold while maintaining near-full capacity.
The Challenge of Hydrogen Evaporation
Converting hydrogen into a cryogenic liquid at minus 253 degrees Celsius is essential for mass transport, as it dramatically reduces volume. However, the process faces a persistent hurdle: heat seepage. As outside heat penetrates storage tanks, liquid hydrogen vaporizes, causing internal pressure to rise. To prevent tank failure, this vapor must be vented, leading to significant product loss during long-term storage and transit.
Previous attempts to mitigate this by inserting porous materials into tanks were largely unsuccessful because the materials occupied valuable space, forcing a trade-off between storage duration and total capacity.
Performance of IRMOF-20 and MIL-53 Materials
The team, led by Professor Oh Hyunchul of UNIST in collaboration with Ewha Womans University and the Technical University of Munich, evaluated two distinct MOF types.
- IRMOF-20: Featuring a large pore volume and a rigid structure, this material enabled a virtual tank to maintain approximately 96.6% of its storage capacity.
- MIL-53: This material, which flexes upon hydrogen adsorption, saw storage capacity drop to roughly 52.8% but demonstrated superior stability at higher temperatures.
The researchers found that IRMOF-20 allows hydrogen to pack more densely inside the pores—estimated at 82 grams per liter—than in its standard liquid state, which offsets the space occupied by the material itself. Neutron scattering experiments confirmed that the rotational motion of hydrogen molecules within these pores is restricted, indicating a tightly packed state.
Tripling Storage Duration in Transport Tanks
The most significant outcome of the study involves the extended lifespan of hydrogen shipments. For a vacuum-insulated transport tank of approximately 56.6 cubic meters, the team reported that the time required for complete depletion increased from 64 days to 221 days. Even under low-vacuum conditions, where insulation performance is typically weaker, the duration stretched from seven days to 22 days.
This improvement is driven by a buffering effect. As hydrogen detaches from the pore walls, it absorbs heat entering from outside the tank, which delays the rise in both temperature and internal pressure.
“When you consider pore volume, the ability to pack hydrogen densely and the way adsorbed hydrogen is released together, we showed that inserting a porous material can cut evaporative losses during transport while keeping storage capacity almost intact.”
Oh Hyunchul, Professor at Ulsan National Institute of Science and Technology
Validation Requirements for Real-World Implementation
Despite the positive simulation data, the researchers emphasized that the technology is not yet ready for immediate industrial application. The team noted that the current findings rely on the theoretical maximum performance of the MOF materials. Further experimental testing is required to determine if these effects remain consistent within actual, physical tanks rather than virtual models.
As Professor Oh noted, further verification is needed to see whether the same effect appears in actual tanks.
The project, which involved contributors from the Institut Laue-Langevin and the Helmholtz-Zentrum Berlin, was supported by South Korea’s Ministry of Science and ICT, the Ministry of Education, and the National Research Foundation of Korea’s BrainLink program.