20 K H₂ Physisorption on Metal-Organic Frameworks with Enhanced Dormancy Compared to Liquid Hydrogen Storage

Liquid hydrogen (LH₂) is the best way of transporting hydrogen, as its high volumetric energy density translates into a significant reduction in hydrogen transportation and refueling operations expenses. However, the phase transformation from liquid to gaseous hydrogen, due to heat leakage of the LH₂ vessel, causes a considerable volume change, results in boil-off losses, and makes long-term storage/transportation problematic. These boil-off losses are a severe drawback for continental transportation through truck tube trailers having evaporative losses of about 3-15% per day (depending on the volume). Herein, hydrogen storage by cryo-adsorption using metal-organic frameworks (MOFs) is proposed as an alternative to reduce boil-off losses and enhance dormancy during continental transportation. The stronger van der Waals interaction operating between adsorbate and adsorbent leads to superdense H₂ adsorption, which compensates for the space occupied by the adsorbent skeleton and results in a volumetric storage capacity comparable to that of LH₂ tanks (∼96%). Depending on the textural properties of MOFs, H₂ desorption can start from 45 K, resulting in an extended dormancy time of the tank system. In addition, the observation of hindered rotational transition (J: 0 → 1) signal in neutron scattering analysis indicates that H₂ are firmly attached and highly immobile on the adsorption sites. The hindered rotation by adsorption at 20 K on MOFs also suggests that the intermolecular separation is less than the bulk liquid (even solid) phase.