Structural and textural control of high-pressure hydrogen adsorption on expandable and non-expandable clay minerals in geologic conditions

Both natural and anthropogenically-generated hydrogen gas occurs in sedimentary rocks and geotechnical barriers. Due to high-pressure conditions, a significant portion of H₂ can be physisorbed in available micropores of clay minerals, which have been proven to control the gas adsorption properties of rocks. This study investigates H₂ adsorption on clay minerals naturally occurring in rocks, by combining the high-pressure H₂ experiments with sample characterization analyzed using low-pressure adsorption of N₂ and CO₂, and structural analysis using X-ray diffraction. We found that H₂ adsorption depends strongly on the mineral texture, which is not related directly to its structure. Most of H₂ is adsorbed in the micropores accessible to CO₂. H₂ intercalates in the smectitic interlayers with a basal spacing larger than 10.8 Å. The density of adsorbed H₂ is about double that of free H₂ gas under given pressure and temperature, effectively increasing the gas storage capacity of rocks.