High-Capacity Volumetric Methane Storage in Hyper-Cross-Linked Porous Polymers via Flexibility Engineering of Building Units.

Adsorbed natural gas (ANG) storage is emerging as a promising alternative to traditional compressed and liquefied storage methods. However, its onboard application is restricted by low volumetric methane storage capacity. Flexible porous adsorbents offer a potential solution, as their dense structures and unique gate-opening effects are well-suited to enhance volumetric capacity under high pressures. This study developes a series of hyper-cross-linked polymers (HCPs) with tunable flexibility by modifying the aliphatic chain length in double-benzene-ring building blocks, employing a cost-effective external crosslinking approach. The resulting flexible polymer, HCP-DPP, exhibits pore expansion under specific methane pressures, producing a high-pressure adsorption isotherm with gate-opening behavior. Combined with its intrinsic dense skeleton, this feature leads to superior volumetric methane storage performance over rigid counterparts. Notably, HCP-DPP achieves a record-high volumetric total uptake of 333 cm STP cm and a working capacity of 291 cm STP cm at 273 K and 100 bar, exceeding the U.S. Department of Energy (DOE) target of 263 cm STP cm. These findings lay a foundation for developing advanced flexible porous adsorbents for practical ANG applications.