Clay minerals and hydrogen: Insights into reactivity, pore structure, and chemical stability

With the increasing global focus on hydrogen as a clean energy source, subsurface hydrogen storage is an important key factor in implementing a full hydrogen economy. Clay minerals are essential for preserving caprock integrity during storage, yet their interactions with hydrogen under high-pressure and high-temperature conditions are not well understood. This study aims to bridge this knowledge gap by examining the geochemical reactivity and structural stability of kaolinite, illite, and bentonite under high-pressure (1450 psi) and high-temperature (75 °C) hydrogen exposure for 90 days. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and low-pressure N₂ adsorption isotherms were employed to assess structural and chemical changes before and after treatment. The results show that kaolinite maintained its structural and chemical stability after hydrogen treatment, with no significant changes in mineral composition or pore structure. Illite shows minimal reactivity with hydrogen, evidenced by slight changes in specific surface area, indicating its suitability for low-risk storage conditions. Bentonite, known for its sensitivity to water and gas, exhibits only minor changes in specific surface area and pore structure. Importantly, no secondary mineral phases or major pore network changes are observed in any of the samples. These findings underscore the resilience of kaolinite and illite under hydrogen-rich conditions, marking them as reliable components for maintaining caprock integrity. Bentonite's slight structural changes suggest it may also perform well under controlled conditions, but further studies under varying gas compositions and extended durations are needed. This study highlights the limited but crucial role of clay-hydrogen interactions in ensuring the safety, efficiency, and long-term viability of geological hydrogen storage systems, laying the groundwork for future research on optimizing storage strategies in diverse geological settings.