Hydrogen release from solid-state ammonia borane (AB, NH3BH3) exhibits a long induction period and requires a relatively high temperature. In the present work, D-mannitol (DM, C6H8(OH)(6)) was used as an additive to enhance the hydrogen release properties of AB. At proton exchange membrane (PEM) fuel cell operating temperatures, the influence of various operating process parameters (temperature and heating rate) and AB-DM ratio has been investigated. In addition, the composition of gaseous products was analyzed to identify the reaction mechanism using mass spectrometry. In particular, the formation of ammonia, which poisons PEM fuel cells, was quantitatively analyzed. Using solid-state nuclear magnetic resonance, solid products were characterized to better understand the mechanism of AB thermolysis. In the presence of DM, the onset reaction temperature decreased to 80 degrees C, whereas dehydrogenation kinetics were significantly improved. With DM as an additive, we obtained a high hydrogen yield of 9.1 wt % (1.75 H-2 equivalent) at the PEM fuel cell operating temperature (90 degrees C).