Packing a liquid-hydrogen tank with IRMOF-20 more than triples its modeled holding time

In the model, 221 days against 64 is a factor of about 3.45 ^[1], or roughly 157 extra days before the tank runs dry ^[2]. The comparison already charges the framework for the room it occupies. A tank packed with IRMOF-20 starts with about 3 percent less hydrogen by volume than a tank of neat liquid ^[3], and it still lasts longer.

Heat gets into even well-insulated tanks. As the liquid warms, hydrogen evaporates and the pressure climbs ^[1]. A metal-organic framework is a crystal full of nanoscale pores that adsorb hydrogen onto their inner surfaces ^[4]. At cryogenic temperatures, the pull of the pore walls keeps the gas confined and slows the pressure rise ^[4].

The small capacity loss comes down to density. Adsorption measurements found hydrogen inside IRMOF-20's pores at an effective density higher than bulk liquid hydrogen ^[11]. That dense packing makes up for much of the volume the solid takes from the tank ^[6].

Park, of TUM, said neutrons suit the problem because "hydrogen has a large neutron-scattering cross section, and inelastic neutron scattering directly probes molecular motion without the optical selection rules that constrain infrared and Raman spectroscopy" ^[13]. The reference is solid parahydrogen, whose rotational spectrum has one sharp line at 14.7 meV. Where that line moves when hydrogen meets a host material tells the experimenters about the forces between them ^[14].

Oh set his own limit on the day counts. "By considering pore volume, hydrogen density, and desorption behavior together, we found that porous materials could reduce boil-off while preserving much of the storage capacity needed for liquid hydrogen transport. 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," he said ^[15].

I think the capacity result is the firmer half of the paper. It rests on adsorption measurements ^[11], while the 221 days comes from a modeled tank under mid-vacuum insulation ^[8]. The thing this doesn't tell you is how a real tank packed with the framework compares with the modeled one. The published account does not give the materials' mass or cost, or say how they hold up over repeated filling and emptying.