Enhancing Volumetric Hydrogen Storage Capacity through Bimodal Packing of MOF Particles

Packing density critically influences the practical hydrogen storage capacity of metal-organic frameworks (MOFs), yet it is often overlooked in volumetric performance evaluations. In this study, we demonstrate that bimodal particle packing provides an effective route to enhance system-level volumetric hydrogen storage by reducing interparticle voids. A V₃(PET) MOF was synthesized in two distinct sizes (∼9 μm and ∼300 nm) to construct a bimodal particle system. Discrete element method (DEM) simulations were used to establish particle-packing design rules and to identify the optimal mixing composition for maximizing packing density. These simulation-guided predictions were then experimentally validated through tapping density measurements and high-pressure H₂ adsorption isotherms. The optimized bimodal mixture achieved a packing fraction of 0.56, compared to 0.42 for unimodal packing, leading to a 33-38% increase in volumetric excess hydrogen uptake at 77 K. Moreover, the bimodal system exhibited an enhanced working capacity of up to 37.7 g/L under pressure-temperature swing adsorption (PTSA) condition (160 K 5 bar to 77 K 100 bar). These results demonstrate particle-level packing engineering as a broadly applicable and experimentally accessible strategy for bridging intrinsic MOF properties with realistic, system-level hydrogen storage performance.