Hydrogen storage potential in underground coal gasification cavities: a MD simulation of hydrogen adsorption and desorption behavior in coal nanopores

Underground hydrogen storage (UHS) in geological formations presents a viable option for long-term, large-scale H 2 storage. A physical coal model was constructed based on experimental tests and a MD simulation was used to investigate the potential of UHS in underground coal gasification (UCG) cavities. We investigated H 2 behavior under various conditions, including temperatures ranging from 278.15 to 348.15 K, pressures in the range of 5–20 MPa, pore sizes ranging from 1 to 20 nm, and varying water content. We also examined the competitive adsorption dynamics of H 2 in the presence of CH 4 and CO 2 . The findings indicate that the optimal UHS conditions for pure H 2 involve low temperatures and high pressures. We found that coal nanopores larger than 7.5 nm optimize H 2 diffusion. Additionally, higher water content creates barriers to hydrogen diffusion due to water molecule clusters on coal surfaces. The preferential adsorption of CO 2 and CH 4 over H 2 reduces H 2 -coal interactions. This work provides a significant understanding of the microscopic behaviors of hydrogen in coal nanopores at UCG cavity boundaries under various environmental factors. It also confirms the feasibility of underground hydrogen storage (UHS) in UCG cavities.