Influence of pore size and isosteric heat of adsorption of some metal-organic frameworks on the volumetric and gravimetric adsorption capacities of hydrogen at room temperature

Metal-organic frameworks (MOFs) are presented as potential candidates to meet the challenge of storing hydrogen at room temperature. However, few hydrogen adsorbents balance high volumetric and gravimetric capacities. In this work, a series of ten MOFs of different topologies were selected to determine on the one hand the characteristics of MOFs capable of balancing the volumetric and gravimetric adsorption capacities of hydrogen at room temperature and on the other hand a correlation between the adsorption properties and the structure of MOF. The influence of characteristics such as free volume, pore diameter, and isosteric heat of adsorption on optimal adsorption at room temperature was evaluated. The results showed that the absolute gravimetric absorption capacity is well correlated with the free volume of the pores. The gravimetric and volumetric capacities of hydrogen absorbents can be balanced and increased by using materials that provide high isosteric heat of absorption. Small pore materials provide high isosteric adsorption heat but adsorb less due to the low free volume.