Room-temperature hydrogen release from activated carbon-confined ammonia borane

In chemical hydrogen storage, nanoconfinement (or nanoscaffolding) is an efficient approach to reduce the size of the particles of boron hydrides such as ammonia borane (AB, NH₃BH₃) at nanoscale while destabilizing its molecular network. It involves the dehydrogenation of AB at temperatures lower than 100 °C and hinders the formation of undesired gaseous by-products such as borazine. Herein, commercial activated carbon (AC) with a specific surface area of 716 m² g⁻¹ and a porous volume of 0.36 cm³ g⁻¹ was used as host material for AB nanoconfinement. A composite activated carbon-ammonia borane (AC@AB) was successfully prepared by infiltration in cold conditions (0 °C). Its dehydrogenation was followed by volumetric method, FTIR, XRD, TGA, DSC, GC–MS and ¹¹B MAS NMR. The most striking result is that the nanoconfined AB, being highly destabilized, dehydrogenates in ambient conditions, even at 3–4 °C. It is demonstrated that dihydrogen is formed according to two pathways that simultaneously take place. The first one is the dehydrogenation through inter- and/or intra-molecular reactions between protonic H and hydridic H of AB, and the second one is the acid-base reaction between protonic H of COO−H groups present on the AC surface and hydridic H of AB.