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

Abstract

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 the dehydrogenation of the AB–Mg or AB–MgH2 sample should likely involve a three-step mechanism, with the formation of a metastable or even unstable magnesium amidoborane phase being a central event.

Solid-Phase Hydrogen Storage Based on NH3BH3-SiO2 Nanocomposite for Thermolysis

“…Although hydrolytic dehydrogenation of chemical hydrides occurs at temperatures lower than 80°C, the requirement of expensive catalysts for hydrolysis, the production of ammonia as a byproduct, and the low H 2 yield are practically incompatible with aerial vehicles [2][3][4][5][6][7][8]. Thermolysis of the chemical hydride does not require a noble metal catalyst and is relatively free of ammonia poisoning [9][10][11]. The H 2 yield through thermolysis of AB, which is a frequently employed hydride compound belonging to the chemical hydride group, can be increased up to 13 wt% [9].…”