Surface modification of mesostructured cellular foam to enhance hydrogen storage in binary THF/H2 clathrate hydrate

Abstract

This study introduces solid-state tuning of a mesostructured cellular foam (MCF) to enhance hydrogen (H₂) storage in clathrate hydrates. Grafting of promoter-like molecules (e.g., tetrahydrofuran) at the internal surface of the MCF resulted in a substantial improvement in the kinetics of formation of binary H₂-THF clathrate hydrate. Identification of the confined hydrate as sII clathrate hydrate and enclathration of H₂ in its small cages was performed using XRD and high-pressure ¹H NMR spectroscopy respectively. Experimental findings show that modified MCF materials exhibit a ∼1.3 times higher H₂ storage capacity as compared to non-modified MCF under the same conditions (7 MPa, 265 K, 100% pore volume saturation with a 5.56 mol% THF solution). The enhancement in H₂ storage is attributed to the hydrophobicity originating from grafting organic molecules onto pristine MCF, thereby influencing water interactions and fostering an environment conducive to H₂ enclathration. Gas uptake curves indicate an optimal tuning point for higher H₂ storage, favoring a lower density of carbon per nm². Furthermore, a direct correlation emerges between higher driving forces and increased H₂ storage capacity, culminating at 0.52 wt% (46.77 mmoles of H₂ per mole of H₂O and 39.78% water-to-hydrate conversions) at 262 K for the modified MCF material with fewer carbons per nm². Notably, the substantial H₂ storage capacity achieved without energy-intensive processes underscores solid-state tuning's potential for H₂ storage in the synthesized hydrates. This study evaluated two distinct kinetic models to describe hydrate growth in MCF. The multistage kinetic model showed better predictive capabilities for experimental data and maintained a low average absolute deviation. This research provides valuable insights into augmenting H₂ storage capabilities and holds promising implications for future advancements.