|Amminex Handheld Hydrogen (H2) tablets|
Researchers at the Technical University of Denmark (DTU) have developed an ammonia-based solid-state hydrogen storage solution: a tablet that can be held in your hand.
The tablet is a metal ammine complex that stores 9.1% hydrogen by weight in the form of ammonia absorbed efficiently in magnesium chloride: Mg(NH3)6Cl2. The storage is completely reversible, and by adding an ammonia decomposition catalyst, hydrogen can be delivered at temperatures below 347º C (656º F). The tablets can be recharged with additional ammonia.
Other metal ammines are possible as well, such as Ca(NH3)8Cl2, although the team spent most of its investigation with the magnesium chloride complex.
Jens Nørskov, Claus Hviid Christensen, Tue Johannessen, Ulrich Quaade and Rasmus Zink Sørensen are the five researchers behind the invention. Together with DTU and SeeD Capital Denmark, they have founded a company—Amminex A/S—which will focus on the further development and commercialization of the technology.
The technology is a step towards making the society independent of fossil fuels. We have a new solution to one of the major obstacles to the use of hydrogen as a fuel. And we need new energy technologies—oil and gas will not last, and without energy, there is no modern society.—Professor Jens Nørskov, director of the Nanotechnology Center at DTU
Ammonia has been explored as a potential hydrogen storage medium since the 1970s. Due to the toxicity of ammonia in its liquid form, most recent work on ammonia as a hydrogen storage solution has focused on solids such as ammonia borane. Researchers at PNNL, for example, are investigating ammonia borane and polyammonia borane. This family of molecules demonstrates hydrogen capacities of > 12 wt%. (Earlier post.)
Metal ammine complexes have been known for more than a century. The DTU team is finding that the kinetics of ammonia adsorption and desorption with the metal ammine complexes are reversible and fast, and that the complex is simple to manufacture and easy to handle.
For use in a PEM fuel cell, the ammonia released from the tablet would then need to be decomposed to hydrogen, and the resulting gas cleansed of any remaining ammonia (probably by passing it over a small amount of unsaturated MgCl2).
|Metal Ammine Complexes as Hydrogen Storage|
|Gravitmetric H2 density|
(wt % H2)
|Volumetric H2 density|
|US DOE Goal 2015||9.0||0.081||9.72|
Should you drive a car 600 km using gaseous hydrogen at normal pressure, it would require a fuel tank with a size of nine cars. With our technology, the same amount of hydrogen can be stored in a normal gasoline tank.—Professor Claus Hviid Christensen, Department of Chemistry at DTU
The DTU research team has just published its first paper on the storage method in the Journal of Materials Chemistry.
(A hat-tip to Distantbody!)
“Metal Ammine Complexes for Hydrogen Storage”, Journal of Materials Chemistry, 2005, (Advance Article), DOI: 10.1039/b511589b
“Hydrogen from Ammonia and Ammonia-Borane Complex for Fuel Cell Applications”, T-Raissi, Ali; Proceedings of the 2002 US DOE Hydrogen Program Review