New material systems with greater hydrogen storage capacity are needed for both transportation and stationary applications. Sandia researchers are studying several materials with the potential to meet this need, including:

• Alanates (AAlH4 where A = Li, Na, K)
• Metal hydrides
• Metal amides (M(NR2)x)

While some of these materials are commercially available, they are generally of low phase purity, consisting of powders with large particle sizes and correspondingly low surface areas. These physical properties can introduce mass-transfer limitations and reduce the kinetics of hydrogen uptake and release.

Our objective is to generate high-quality, high surface-area materials for hydrogen storage on a scale large enough to study not only material properties but also system development. We are developing several chemical solution routes to produce the materials listed above. For the M(NH₂)x system in particular, we are reacting a variety of alkali precursors with ammonia to form the desired amide,

MR + (xs) NH₃ (g) M(NH₂)_x + HR
M° + (xs) NH₃ (l) M(NH₂)_x

We are investigating the high purity synthesis of NaAlH4 and the various congener derivatives through the simple solution route,

AH + AlX₃ AAlH₄

The synthesized alanates are solubilized and then precipitated through solvent manipulation, ligation, and other process variables. We are developing continuous precipitation schemes to produce powders with controlled, reproducible properties in quantities sufficient to meet the needs of the project.

Contacts:
Tim Boyle
tjboyle@sandia.gov
(505) 272-7625

Jim Voigt
javoigt@sandia.gov
(505) 845-9044