Hydrogen and Cushion Gas Adsorption–Desorption Dynamics on Clay Minerals

Transitioning toward a hydrogen (H₂)-centric energy paradigm necessitates understanding the adsorption properties of clay minerals, essential constituents of reservoirs and caprocks, for efficient geological H₂ storage. This study examines the adsorption characteristics of H₂ on various clay minerals (montmorillonite, illite, chlorite, kaolinite, and sepiolite) at different temperatures and the adsorption of cushion gases (N₂, CH₄, and CO₂) under reservoir conditions (313.15 K, up to 10 MPa). The results indicate that sepiolite demonstrates superior adsorption capacity under all tested conditions, surpassing montmorillonite by over 12 times at 313.15 K for H₂. Illite, chlorite, and kaolinite exhibit negligible H₂ adsorption. Thermodynamic analysis reveals that H₂ adsorption on clay minerals is a nonspontaneous and exothermic physisorption process. H₂ loss due to adsorption hysteresis in montmorillonite and sepiolite is 42.19 and 3.56%, respectively. Sepiolite may exhibit more predictable and stable sorption properties under repeated pressure variations. The H₂ adsorption capacity of montmorillonite and sepiolite is merely 0.4 and 4.5% of that of CO₂, respectively. This study provides valuable insights for selecting clay minerals and cushion gases for efficient geological H₂ storage and natural hydrogen exploration.