Facet-Dependent Water Clustering in ZIF-8 Enables High-Efficiency Methane Storage

Achieving high volumetric capacity for solid-state methane (CH₄) storage under mild conditions remains a challenge for vehicular applications. While metal-organic frameworks (MOFs) demonstrate excellent CH₄ physisorption kinetics, most fail to meet the U.S. Department of Energy (DOE)'s target of 263 v/v at pressures below 6.5 MPa. Here, we propose a strategy that engineers the exposed crystal facet of MOF to promote the clathrate formation on the surface, achieving an efficient combination of MOF adsorption and clathrate CH₄ storage. We find that the exposed {100} facets of cubic ZIF-8 can induce polar water molecules to assemble into structured clusters and further encapsulate CH₄ molecules, attributed to electrostatic interactions and the van der Waals effect. Finally, the cubic ZIF-8 boosts the massive generation of CH₄ clathrate on the exposed facets and maintains the physical adsorption capacity for CH₄ within the pores. In the fixed-bed system, pre-wetted cubic ZIF-8 can efficiently store CH₄ with a recorded capacity of 343 v/v at 5 MPa, surpassing the DOE's target.