(256f) Safe, Efficient Storage of Hydrogen in Liquid Ammonia and Ammonia-Based Solid Chemicals

Pure anhydrous ammonia (NH3) provides an excellent storage medium for hydrogen, and two known solid organic chemicals related to ammonia, urea and guanidine, are also good storage media. Anhydrous ammonia is about 18 percent hydrogen by weight percent and has all of the advantages associated with a liquid fuel?high volumetric density, easy to store, easy to pump, easy to transport, and easy to deliver. It also has an existing and proven distribution infrastructure and is one of the highest tonnage chemicals produced in the world. Furthermore, gaseous hydrogen can be readily produced (reformed) from anhydrous ammonia at the highest efficiency of any hydrogen-containing chemical. On the other hand, it is well known that ammonia is toxic which results in some handling/delivery safety concerns. We will discuss safe handling of anhydrous ammonia. It turns out as well that both urea and guanidine (solids at standard temperature and pressure) have essentially zero toxicity, are not explosive, and do not exhibit any other public or environmental hazard. Both are high in hydrogen content via their ammonia content, and both can be reacted with water under appropriate conditions to provide ammonia, which can then be reformed to hydrogen as necessary. We will discuss the features of these two chemicals and their potential applications as safe, energy-dense hydrogen energy carriers.