Liquid hydrogen extended dormancy using MOFs and MOF/carbon hybrids

Abstract

Liquid hydrogen (LH2) systems are highly susceptible to boil-off (BO) losses due to their extreme cryogenic operating conditions, with temperatures below 20K. This study examines the potential use of metal organic frameworks (MOFs), both in their pristine form and as hybrids with carbon-based materials, as cryo-adsorbents to mitigate BO. MOFs combined with graphene oxide (GO), exfoliated graphite (EG), and carbon quantum dots (QDOTs) are assessed with respect to their capacity to enhance LH2 retention within their pore networks and thereby extend the dormancy period. To the best of current knowledge, this is the first systematic assessment of these MOF‑carbon hybrids for BO mitigation. The studied materials allowed an increase in the BO temperature at 1bar, rising from 20K for the empty tank to 64K for the material providing the longest dormancy under pore-saturation conditions. In particular, the MIL-101(Cr)/GO hybrid exhibited a pronounced effect compared to the pure MOF, MIL-101(Cr), as the development of microporosity increased the BO temperature from 31 to 44K. Microporosity was identified as a key factor governing dormancy extension, with a linear relationship between their average pore diameter and the corresponding increase in the BO temperature. These results provide key insights for the design of cryo-adsorption systems, underscoring the essential interplay between porosity and tank-volume constraints in the optimization of H2 storage materials. Keywords: Metal-organic frameworks (MOFs); Boil-off hydrogen; Adsorption; Liquid hydrogen; MOF hybrids