Promoting hydrogen storage under mild conditions by binary clathrate hydrates in porous activated carbon

Hydrogen (H 2 ) clathrate is an ideal solid-state medium for hydrogen storage, yet practical applications are hindered by high formation pressures or insufficient storage capacities with conventional promoters. To address these challenges, binary methane-hydrogen clathrates have emerged as a promising high-energy-density fuel capable of bridging existing natural gas infrastructure with future hydrogen-based energy systems. Using molecular dynamics simulations, this study investigates a two-tiered promotion strategy for effective hydrogen storage under milder conditions (e.g., 260 K and 100 bar), combining methane (CH 4 ) as a thermodynamic promoter and nanoporous activated carbon as a host material to leverage advantageous confinement effects. By analyzing formation and dissociation of clathrates under systematic variation of temperature and pressure, favorable conditions for H 2 enclathration in different cage configurations were identified, including H 2 -occupancy in 5 12 cages and CH 4 -presence in both 5 12 and 6 2 5 12 cages at 270 K. Clathrate dissociation temperatures varied by up to ∼ 30 K depending on local pore size and cage configuration. The results yield a predictive phase diagram for the formation of binary CH 4 –H 2 clathrates in porous media. Furthermore, critical pore sizes of 2.5 nm for stability and 4.7 nm for formation of the binary clathrates was established, informing future material synthesis and highlighting the metastability of gas clathrates. These insights into the relationship between clathrate structure, pore size, and gas storage mechanisms provide a molecular-level foundation for H 2 storage in porous materials, and support that a dual-storage mechanism combining micropore physisorption and meso-/macro-pore enclathration can be utilized to enhance storage efficiency. • Binary CH 4 –H 2 clathrates form in porous carbon under mild conditions. • Methane acts as a promoter enabling hydrogen enclathration. • Molecular simulations reveal phase diagram for nanoconfined binary clathrate. • Critical pore size identified for stable clathrate formation and dissociation. • Dual-storage mechanism via physisorption and enclathration enhances hydrogen storage.