Integrating Organic Hydrogen Carriers into Reservoir–Caprock Systems: A Promising Subsurface Hydrogen Storage Strategy

Efficient and secure storage solutions are essential for the long-term viability of the hydrogen (H2) industry. The reversible hydrogenation–dehydrogenation activity and liquid-phase handling benefits of organic hydrogen carriers (OHCs) have made them an attractive method for large-scale hydrogen storage and transfer. As a new approach to increased subsurface hydrogen storage capacity, this study examines the interfacial tension (IFT) and wettability (advancing and receding contact angles) of a hydrogenated OHC (methylcyclohexane, MCH) and a dehydrogenated OHC (toluene) on mica as a proxy caprock in the presence of 1 M NaCl brine at reservoir-relevant temperatures (298–343 K) and pressures (1–20 MPa). The interfacial exchanges and physico-thermal variations are evaluated via total organic carbon (TOC) assessment, atomic force microscopy (AFM), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). The results highlight the importance of caprock-fluid interactions in controlling the structural trapping and sealing integrity in OHC-based hydrogen storage. At higher temperatures, the effects of increased pressure on the nonwetting behavior and sealing integrity are weaker, which makes leaks more likely. Structural trapping and secure long-term hydrogen containment are made possible by regulated OHC-caprock interactions and interfacial forces, with toluene providing a better candidate than MCH due to its lower IFT and greater nonwetting characteristics. This study provides a deepened knowledge of the interfacial mechanisms governing containment and storage stability, and conclusively demonstrates that integrating OHCs into geological formations with a caprock is an effective and reliable means for storing hydrogen underground in a sustainable manner.