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.