Rapid hydrogen enclathration and unprecedented tuning phenomenon within superabsorbent polymers

Clathrate hydrate has emerged as a potentially viable storage medium for efficient hydrogen storage, owing to its eco-friendly characteristics and high hydrogen storage capacity. However, it is essential for its practical application to address the challenges posed by harsh thermodynamic formation conditions and slow formation kinetics for hydrogen hydrate. Here, we introduce the utilization of superabsorbent polymers (SAPs) as a dispersion matrix for tetrahydrofuran (THF) solutions to develop a method for rapid hydrogen enclathration. We investigated two distinct synthetic pathways, solution-borne and hydrate-borne routes. We also explored the relationship between hydrogen uptake/storage capacity, varying THF solution concentration within SAPs, and synthetic pathways for binary THF–hydrogen hydrates. The hydrogen storage capacity after 200 min enclathration reaction was relatively low for 1.0 mol% THF cases but significant for 5.56 mol% THF cases in hydrate-borne route (around 20 mmol H₂/mol water), highlighting its potential for hydrogen storage material. The spectroscopic analysis revealed that the tuning phenomenon in THF 1.0 mol% hydrate was only observed in the solution-borne route, which facilitated hydrogen enclathration in partially vacant large cages of sII hydrates. It was striking that the tuning phenomenon was also observed in THF 5.56 mol% hydrate synthesized in both solution-borne and hydrate-borne pathways. Through phase equilibria measurements, we confirmed that less than 5.56 mol% of THF participated in forming binary hydrates. The different water and THF absorbability of SAPs resulted in a non-uniform distribution of THF solution within SAPs, causing the unprecedented tuning phenomenon. These findings provide valuable insights into the potential of SAPs for rapid hydrogen enclathration media, emphasizing the importance of understanding synthetic pathways and solution absorption properties for optimized hydrogen storage.