Safe Packaging of Ammonia for Compact Hydrogen Sources

The U.S. Army has funded development of compact hydrogen generators that extract hydrogen from anhydrous ammonia. However, use of these ammonia-based hydrogen generators will likely be restricted unless the ammonia can be stored such that the potentialfor a dangerous ammonia release is minimal.We have studied a variety of approaches for safe storage of ammonia and reached the conclusion that monolithic, closed-cell foam materials offer the desired characteristics of compact and lightweight ammonia storage with relatively little safety risk.Lightweight, closed-cell foam materials will be used to fill the ammonia-storage tank and thereby reduce the rate of ammonia release in the event of tank failure. Scoping tests demonstrate that closed-cell foam materials offer a promising method forimproving the safety of ammonia storage.We propose development of an ammonia-storage tank filled with closed-cell foam monolith. Based on scoping tests, we predict our storage tank will have an ammonia capacity of 500 g (1.5 kWhe), an overall volume of 1.2 liters, and a total mass of less than950 g (including 500 g ammonia). The maximum ammonia release rate will be low enough to minimize safety concerns yet high enough to supply the ammonia-based hydrogen generators. Development of a compact, lightweight, and safe means for storing anhydrous ammonia will eliminate the principal drawback of ammonia-based hydrogen sources for fuel-cell-based power supplies. Once an appropriate ammonia-storage system is available, theexisting ammonia-based hydrogen generators can rapidly move toward deployment in the U.S. Military for compact power supplies. Many commercial, compact-power applications will also become feasible once safe ammonia storage is available. In addition,these ammonia-storage foams may find application for safe storage of other toxic and flammable chemicals, such as propane.