Screening of Metal-Organic Frameworks for Dihydrogen Adsorption and Separation

This work investigates the hydrogen isotopologue separation performance of metal-organic frameworks (MOFs) focusing on the roles of open metal sites (OMS), pore structure, and cryogenic flexibility. Stronger interactions with hydrogen proven possible by mixed metal MOFs result in higher isosteric heat of adsorption (Qads) and enhanced selectivity, particularly higher than cryogenic boiling temperatures of dihydrogen isotoplogues (~ 77 K). Ultramicroporous MOFs also show increased Qads but reduced uptake, suggesting that selectivity and uptake are traded off. Interestingly, experiments using thermal desorption spectroscopy (TDS) show that MOFs exhibit temperature-dependent cryogenic flexibility, with pore opening at 77 K and pore closing at 30 K resulting in a significant change in adsorption behavior. These insights into rational MOF design strategies for efficient isotopologue separation could have important potential applications ranging from hydrogen purification to fusion energy and quantum sieving material development.