Molecular simulations of hydrogen diffusion in underground porous media: Implications for storage under varying pressure, confinement, and surface chemistry conditions

• Published in: International journal of hydrogen energy Vol. 65; no. C; pp. 540 - 547
• Main Authors: Oliver, Madeleine C., Zheng, Ruyi, Huang, Liangliang, Mehana, Mohamed
• Format: Journal Article
• Language: English
• Published: United Kingdom Elsevier Ltd 02.05.2024; Elsevier
• Subjects: Adsorption behavior; Hydrogen underground storage; Molecular dynamics simulation; Nanoporous media; Self-diffusion; Surface composition; Adsorption behavior; Molecular dynamics simulation; Surface composition; Nanoporous media; Hydrogen underground storage; Self-diffusion
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2024.04.068

Assessing the feasibility of porous formations for hydrogen geo-storage demands a comprehensive understanding of hydrogen (H2) transport behavior in porous media at subsurface conditions. In this study, we employ molecular dynamics simulations to evaluate the effects of pressure (20–500 atm), pore size (2–20 nm), and surface composition on H2 diffusion and interactions within organic and inorganic slit pores. Our analysis of H2 density profiles and interaction energies reveals a distinct preference for H2 molecules to adsorb more readily onto graphene surfaces than kaolinite surfaces. However, self-diffusion results demonstrate that H2 molecules interact relatively weakly with both substrate types. Further insights are provided by velocity autocorrelation functions, emphasizing the occurrence of wall-mediated collisions as H2 molecules diffuse along the pore surfaces, particularly within kaolinite. This highlights the significance of surface roughness in mitigating H2 loss via diffusion in subsurface nanopores, given the small molecular size of H2 and its limited interactions with both organic and inorganic materials. Furthermore, the results demonstrate that self-diffusion coefficients in both pore types increase with pore size and decrease with pressure. Notably, surface composition plays a critical role in low-pressure environments, with self-diffusion coefficients beginning to converge beyond a pressure of 100 atm. Self-diffusion coefficients also become less sensitive to slit aperture beyond a pressure of 50 atm. In high-pressure environments, hydrogen transport is governed by thermal collisions between gas molecules, leading to negligible property variations between pore types. These findings hold significance in the investigation of efficient H2 storage within porous media and caprock formations. •H2 molecules adsorb more readily onto graphene surfaces than kaolinite surfaces.•H2 molecules interact relatively weakly with both graphene and kaolinite.•Surface roughness is a fundamental property governing potential H2 loss.•H2 self-diffusion generally increases with pore size and decreases with pressure.•Surface composition plays a critical role in H2 transport at lower pressures.