Impact of Perchloric Acid on the Thermodynamic Stability of THF, CH4/THF, and H2/THF Hydrates and Hydrogen Incorporation into H2/THF Hydrates

Abstract

Hydrate-based hydrogen storage (HBHS) has emerged as a promising alternative for safe and reversible H2 storage under milder conditions than conventional high-pressure or cryogenic approaches. However, the storage capacity of mixed H2/THF hydrates remains limited by slow H2 diffusion and low cage occupancy. In this work, the influence of perchloric acid (HClO4) on the thermodynamic stability and H2 incorporation of THF-based hydrates was investigated under coformation conditions relevant to HBHS. A combined calorimetric and spectroscopic approach was employed. Differential scanning calorimetry was first used to investigate the thermodynamic stability of pure THF hydrates and mixed CH4/THF hydrates as reference systems, allowing the effect of HClO4 on the hydrate host lattice to be isolated independently of H2. The stability of mixed H2/THF hydrates was then examined by the establishment of the phase equilibrium diagram in the presence of HClO4, while in situ Raman microspectroscopy was used to probe the incorporation of H2 within hydrate cages. Calorimetric results show that HClO4 slightly lowers the dissociation temperatures of THF-based hydrates, indicating a moderate destabilization of the host lattice. In contrast, Raman spectroscopy reveals a strong enhancement of H2 incorporation, with the normalized intensity of encapsulated H2 increasing by a factor of 5–6. This behavior provides a favorable compromise between hydrate stability and H2 incorporation, highlighting controlled chemical modification of the hydrate lattice as a promising strategy for improving HBHS.