Hydrogen Generation from Noncatalytic Hydrothermolysis of Ammonia Borane for Vehicle Applications

Ammonia borane (AB) is a promising hydrogen storage material as it contains 19.6 wt% hydrogen. To release hydrogen from AB, current methods require either high temperatures or expensive catalysts. We recently proposed and demonstrated a new method involving noncatalytic hydrothermolysis of AB solutions, where heating lean solutions of AB in water at ~135 °C under moderate argon pressure (~10 atm) generates 1 equivalent of H₂ by thermolysis and 2 equivalent by hydrolysis. In this paper, the hydrothermolysis approach is studied over a wide range of AB concentrations (6-88 wt%), at pressure 14.7 and 200 psia, and temperature 80-135 ^oC. It is shown that with increasing AB concentration, the H₂ yield increases, while HD yield decreases, so that the role of thermolysis, as compared to hydrolysis, increases. This approach provides the maximum hydrogen storage capacity up to 10.5 and 11.9 wt%, along with rapid kinetics, at T_reactor ~ 85 ^oC and at pressure 14.7 and 200 psia, respectively. To our knowledge, on a material basis, the AB hydrothermolysis process is the first one to provide such high hydrogen yield values at below PEM fuel cell operating temperatures. The results indicate that the proposed method is promising for hydrogen storage, and could be used in fuel cell based vehicle applications.