Quartz-Fluid Interfacial Tension of Hydrogenated and De-Hydrogenated Organic Hydrogen Carriers: Implications for Hydrogen Geological Storage

Abstract A hydrogen-based economy necessitates effective hydrogen storage, and Organic Hydrogen Carriers (OHCs) represent a promising solution to this challenge. OHCs offer a practical, safe, and efficient means for handling, distributing, and storing hydrogen, particularly in geological formations. Their performance in subsurface environments, however, depends significantly on interfacial properties at the pore scale—especially the equilibrium contact angle (θE) and interfacial tensions between solid-brine (γSL) and solid-OHC (γSOHC) interfaces. These parameters influence how OHCs interact with the rock matrix and determine their storage capacity and confinement stability. Due to the technical difficulty of direct measurement, these interfacial properties are often calculated using theoretical models such as Young’s and Neumann’s equations. In this study, interfacial parameters were theoretically determined for a quartz substrate in contact with brine and two OHC phases: toluene (de-hydrogenated form) and methylcyclohexane, MCH (hydrogenated form). The analysis was conducted across reservoir-relevant conditions (temperatures of 298–343 K, pressures of 1–20 MPa, and 1 M NaCl salinity), using observed advancing and receding contact angles and fluid-fluid interfacial tension (IFT) as input. Results revealed that with increasing pressure, the contact angle θE increases while γSOHC decreases, indicating enhanced wettability and reduced IFT due to stronger interactions between OHC molecules and quartz surfaces. Conversely, γSL remains largely unaffected by pressure changes due to the minor density variation of brine. As temperature rises, both θE and γSL increase, while γSOHC decreases. These temperature and pressure trends influence how efficiently OHCs can be confined and distributed within reservoir pores. Additionally, toluene demonstrated higher θE and lower γSL and γSOHC values than MCH under similar conditions, attributable to its higher density. For instance, at 343 K and 5 MPa, toluene has a density of 0.82478 g/ml compared to 0.73623 g/ml for MCH. These findings highlight the potential of quartz-rich sandstone formations for secure and efficient OHC-based hydrogen storage. Optimizing interfacial interactions between OHCs and geological substrates is crucial for advancing hydrogen geo-storage technologies and supporting the transition to sustainable energy systems.