Hydrogen pellets

As a potential energy carrier, molecular hydrogen can power fuel cells and heat engines, and has only water as its byproduct. But before hydrogen can replace fossil fuels, several technical challenges need to be met. (See the article in Physics Today, December 2004, page 39 .) The challenge of storing hydrogen in a safe, high-density form is being approached in different ways; now, another possible solution has been found. Researchers at the Technical University of Denmark in Lyngby have infused ammonia, NH₃, into a metallic salt that can then be compacted into pellets, as shown here. This solid form of hydrogen storage is completely reversible: The ammonia is released and decomposed with the help of a catalyst, and the porous salt can then easily absorb a fresh supply of ammonia—more than 50% of its weight, or 9% hydrogen by weight. Although the pellets desorb ammonia so slowly that you can carry them in your pocket, free ammonia is a strong irritant and its release from the solid must be safely contained. The scientists point out, however, that the only byproduct of their process is molecular nitrogen. In addition, ammonia is easier to decompose into CO _x -free hydrogen than either hydrocarbons like gasoline and diesel, or alcohols like methanol. (C. H. Christensen et al., J. Mat. Chem., in press.)