Hydrogen for Vehicle Applications from Hydrothermolysis of Ammonia Borane: Hydrogen Yield, Thermal Characteristics, and Ammonia Formation

Among chemical hydrides, ammonia borane (AB) is of interest as a hydrogen storage material due to its high hydrogen capacity (19.6 wt %). In this paper, our recently developed hydrothermolysis process was investigated over a wide range of AB weight percentages (wt %) in water, pressures, and heating rates. It was found that hydrogen yield and thermal characteristics were influenced by these operating conditions. Ammonia generation was also observed during AB hydrothermolysis, where 14−53% of AB was converted to NH3 depending on the reaction conditions. It is remarkable that some AB (2−4%) was converted to NH3, which must be removed for use in proton exchange membrane (PEM) fuel cells, even by neat thermolysis. It was also found that during the hydrothermolysis reaction at Treactor of 85 °C, the Tsample can exceed 500 °C, where AB can be completely decomposed to boron nitride (BN). The 11B NMR characterization of hydrothermolysis products showed compounds with B−O and B−N bonds. This paper suggests directions for future research to identify optimal conditions, where the hydrothermolysis process provides the best balance between H2 yield and undesirable products, for PEM fuel cell vehicle applications.