Rapidly Releasing over 9 wt % of H2 from NH3BH3–Mg or NH3BH3–MgH2 Composites around 85 °C

It is ideal that the hydrogen storage materials for vehicular applications can desorb substantial amounts of hydrogen below 85 °C, the operating temperature of polymer electrolyte membrane (PEM) fuel cells. Ammonia borane (NH3BH3, AB for short), because of its intriguingly high hydrogen density (i.e., 19.6 wt %) and moderate thermal stability, is widely regarded as a promising on-board hydrogen storage medium. However, at this temperature, both its dehydrogenation kinetics and deliverable H-capacity are far from meeting the requirements for practical applications. Here, we report that the Mg- or MgH2-modified AB can deliver over 9 wt % of H2 within 1.5 h at approximately 85 °C. Such pronounced dehydrogenation properties are found to be enabled by the combination of three factors, including partial phase transition of normal AB to its mobile phase AB* in the starting material, adequate sample thermal conductivity, and sufficiently intensive external energy input. A further mechanistic study indicates that ...