Polyol-Assisted Dehydrogenation and Regeneration of Ammonia Borane: A Step toward the Identification of a Sustainable Hydrogen Storage Material

Hydrogen is a promising fuel for future energy systems, but problems are associated with its storage and transportation because of its low density and high diffusivity. Chemical hydrogen storage has shown highly promising properties, such as boron-containing compounds, which are typical examples. Boron-containing compounds have exceptional properties for chemical hydrogen storage, and in recent years, their hydrolytic and thermolytic dehydrogenation has drawn significant attention. Ammonia borane (NH3BH3, AB), among them, has a high hydrogen storage capacity. However, thermal decomposition of ammonia borane also involves the release of ammonia diborane and borazine as harmful byproducts. Additionally, the postheated product of AB thermolysis, a stable BN compound, is challenging to regenerate directly. Digestion of the BN compound to BO-based compounds leads to a lower yield of ammonia borane when regenerated. Therefore, controlled thermolysis turns out to be a satisfactory combination of dehydrogenation and regeneration of ammonia borane. In this work, the experiment of ammonia borane with ethylene glycol, glycerol, and triethanolamine at 100 °C was performed with successive additions of ammonia borane. NMR and mass spectrometry analysis have been studied to observe the suppression of byproduct gases and increased hydrogen generation. Our work reveals that the strong intermolecular hydrogen bonding of polyols diminishes uncontrolled dehydrogenation of the ammonia borane–polyol mixture, which can be activated by a nominal increase in temperature. The regeneration of ammonia borane from the postdehydrogenated or remaining compounds after dehydrogenation, in the presence of lithium aluminum hydride, was carried, which resulted in ammonia borane with a purity of 83%.