(330d) High Hydrogen Yield From Ammonia Borane Hydrothermolysis for Fuel Cell Based Vehicles

The widespread use of PEM fuel cells is hindered by the absence of a practical, high density hydrogen fuel source. Among various alternatives, chemical methods of hydrogen storage provide high specific energy at relatively easy storage conditions. Ammonia borane (AB) is a promising hydrogen storage material as it contains 19.6 wt% hydrogen. To release hydrogen from AB, thermolysis and catalytic hydrolysis are usually employed, but these methods require either high temperatures or expensive catalysts. Hydrothermolysis of AB [1], investigated in the present work, allows for hydrogen generation (from both AB and water) at moderate temperatures and without the use of catalyst. This method involves external heating of aqueous AB solutions to temperatures 70-85 °C, under argon pressure (~ 10 bar). To clarify the reaction mechanism, D₂O was used instead of H₂O in certain experiments. It was shown that with increasing AB concentration, the H₂ yield increased, while HD yield decreased. Thus the role of thermolysis (H₂ yield), as compared to hydrolysis (HD yield), increases with AB concentration. This approach provides maximum hydrogen storage capacity of 11 wt%. To our knowledge, the AB hydrothermolysis process is the first one to provide such high hydrogen yield values at T<85 °C. The results indicate that the proposed method is promising for hydrogen storage, and could be used in fuel cell based vehicles.

References:

[1] Diwan, M., Diakov, V., Shafirovich, E., Varma, A., ?Noncatalytic Hydrothermolysis of Ammonia Borane?, International Journal of Hydrogen Energy, Vol. 33, 2008, pp 1135-1141.