Hydrogen Diffusion in Slit Pores: Role of Temperature, Pressure, Confinement, and Roughness

Diffusion of hydrogen (H2) is important to understand the leakage risk and transport behavior for H2 geologic storage. We applied molecular dynamics simulations to investigate the influencing factors of H2 diffusion in the slit pores of calcite, hematite, and quartz, owing to their abundance. It is revealed that the H2 self-diffusion coefficient increases with the temperature, regardless of the type of pore minerals. The diffusion of H2 in the 20 nm slit pores falls into the bulk diffusion regime when the pressure is 10 MPa. The self-diffusion of H2 decreases with pressure in all three types of slit pores, following a power law model with the exponents ranging from −0.825 to −0.964. Furthermore, the impact of confinement on H2 diffusion is more pronounced for the slit pores with stronger interactions with H2-like calcite. The role of surface roughness in H2 diffusion depends on the slit aperture. The rough surface enhances H2 diffusion in the larger slit pores due to the enlarged effective pore space, whereas it weakens H2 diffusion in the small slit pores due to stronger adsorption. These findings will fill the knowledge gap on the coupling effect of different factors influencing H2 diffusion.