Automotive storage of hydrogen in alane

Although alane (AlH3) has many interesting properties as a hydrogen storage material, it cannot be regenerated on-board a vehicle. One way of overcoming this limitation is to formulate an alane slurry that can be easily loaded into a fuel tank and removed for off-board regeneration. In this paper, we analyze the performance of an on-board hydrogen storage system that uses alane slurry as the hydrogen carrier. A model for the on-board storage system was developed to analyze the AlH3 decomposition kinetics, heat transfer requirements, stability, startup energy and time, H2 buffer requirements, storage efficiency, and hydrogen storage capacities. The results from the model indicate that reactor temperatures higher than 200 °C are needed to decompose alane at reasonable liquid hourly space velocities, i.e., > 60 h−1. At the system level, a gravimetric capacity of 4.2 wt% usable hydrogen and a volumetric capacity of 50 g H2/L may be achievable with a 70% solids slurry. Under optimum conditions, ∼80% of the H2 stored in the slurry may be available for the fuel cell engine. The model indicates that H2 loss is limited by the decomposition kinetics rather than by the rate of heat transfer from the ambient to the slurry tank.