Recyclable Dehydrogenation/Regeneration of Ammonia Borane Nanoconfined in Amino-Functionalized ZIF-8 with 3-Amino-1,2,4-triazole

Ammonia borane (AB, NH3BH3) is considered a promising hydrogen storage material due to its high hydrogen capacity of 19.6 wt %. However, AB thermolysis for complete dehydrogenation requires high temperature. Moreover, AB regeneration is challenging because of the strong B–N bonding in the spent fuel, which causes low regeneration yield. It has been reported that combined effects of size control and basic functionality effectively facilitate AB dehydrogenation and regeneration. In this study, we focused on nanoconfined AB in porous zeolitic imidazolate frameworks (ZIF-8). The ligands of 2-methylimidazole (2-mlm) in ZIF-8 were partially replaced with 3-amino-1,2,4-triazole (ATZ) in order to introduce amino functionalities. The AB@ZIF composites successfully showed 50 and 20 °C lower onset and apex dehydrogenation temperatures, respectively, than the neat AB case. Since the AB dehydrogenation temperature can be controlled by nanoconfinement size, the interaction between primary amines on ATZ and AB may forcibly limit AB molecules from aggregating near the ZIF aperture, forming small particles. For AB regeneration, the spent AB confined in ZIFs can be regenerated by reacting with only liquid ammonia but not N2H4. It is expected that nanoconfined AB results in a low degree of polymerization in the spent fuel rich in B–H species.