Hydrogen and Cushion Gas Adsorption-Desorption Dynamics on Clay Minerals

Transitioning toward a hydrogen (H-2)-centric energy paradigm necessitates understanding the adsorption properties of clay minerals, essential constituents of reservoirs and caprocks, for efficient geological H-2 storage. This study examines the adsorption characteristics of H-2 on various clay minerals (montmorillonite, illite, chlorite, kaolinite, and sepiolite) at different temperatures and the adsorption of cushion gases (N-2, 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 H-2. Illite, chlorite, and kaolinite exhibit negligible H-2 adsorption. Thermodynamic analysis reveals that H-2 adsorption on clay minerals is a nonspontaneous and exothermic physisorption process. H-2 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 H-2 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 H-2 storage and natural hydrogen exploration.