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

Abstract 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 3 STP cm −3 and a working capacity of 291 cm 3 STP cm −3 at 273 K and 100 bar, exceeding the U.S. Department of Energy (DOE) target of 263 cm 3 STP cm −3 . These findings lay a foundation for developing advanced flexible porous adsorbents for practical ANG applications.