General Relationship between Hydrogen Adsorption Capacities at 77 and 298 K and Pore Characteristics of the Porous Adsorbents

The hydrogen adsorption isotherms of six metal–organic frameworks (MOFs) and three microporous carbons, measured at 77 K (up to 1 bar) and 298 K (up to 100 bar), have been systematically examined for correlations with their pore characteristics. From the obtained correlations, H2 adsorption was found to occur preferentially in ultrafine pores at both 77 K (≤1 bar) and 298 K (100 bar), irrespective of the adsorbent. This represents the first experimental evidence that ultrafine pores in MOFs improve the efficiency of H2 adsorption at 298 K and at high pressures, indicating that that the low H2 storage capacities of reported ultrahigh microporous MOFs at 298 K result from the prominence of micropores with diameters 1–2 nm, which are inadequate at 298 K and high pressures. Furthermore, these correlations suggest strong links between the H2 storage capacities at 77 and 298 K, which offer an easy method for predicting H2 adsorption capacities under unapproachable conditions. This study provides guidance in the development of new MOFs or other adsorbents with an optimized H2 storage capacity at near-ambient temperatures and a swift screening method of newly synthesized porous adsorbents.