Noncatalytic hydrothermolysis of ammonia borane

Hydrolysis of ammonia borane (AB) is attractive as a chemical method for hydrogen storage. The use of catalysts is, however, usually required. In the present paper, two new methods for releasing hydrogen from AB and water are investigated which do not involve any catalyst. One method is based on combustion of AB mixtures with nanoscale aluminum powder and gelled water. It is shown experimentally that these mixtures, upon ignition, exhibit self-sustained combustion with hydrogen release from both AB and water. The other method involves external heating of aqueous AB solutions to temperatures 120 °C or higher, under argon pressure to avoid water boiling. To clarify the reaction mechanism, isotopic experiments using D2O instead of H2O were conducted. It is shown that heating AB/D2O solution to temperatures 117–170 °C releases 3 equiv. of hydrogen per mole AB, where 2–2.1 equiv. originate from AB and 0.9–1 equiv. from water. The prospects of both methods for hydrogen storage are discussed.