Metal hybrides composites
Why we do this
Some metal alloys, often referred to as metal hydrides, will reversibly absorb and desorb H2. As such they are often considered for H2 storage and compression applications. This often requires the hydride to be contained within a pressure vessel. As the metal alloys absorb hydrogen they expand. This places an upper limit on the safe filling capacity of hydride containing vessels. As these vessels are filled and emptied, the hydride will break down into a fine powder. Thus, as the vessel is cycled over its lifetime, performance often drops, both as a result of deterioration of the hydride, but also deterioration of hydride distribution within the vessel, reducing heat transfer efficiency.
Absorption of hydrogen is an exothermic process. In order to fill a hydride vessel in realistic timeframes, heat must be removed from the system (and reverse for discharge of H2). Heat transfer through the vessel into or from the hydride material is often a limiting factor for these systems.
Various modifications have been suggested to hydride vessels (metal fins etc…) to improve heat transfer characteristics. These modifications however can significantly increase the cost and complexity of hydride storage vessels. Cheaper alternatives involve mixing the hydride with conductive materials. To improve the handling capability of the hydride and contain its expansion, mixtures with polymers have also been suggested.
At CSIRO we are progressing a collaborative project exploring three pathways for improving heat transfer in metal hydride containing vessels by fabricating the hydride into a composite
- Polymer based composites
These composites combine the metal alloys with polymeric materials. These can be fabricated into various shapes and sizes. The polymer can absorb the expansion of the alloys as they absorb H2
- Graphite based composites
These composites combine the metal alloys into compressed discs with thermally conductive materials such as expanded natural graphite
- Carbon fiber-based monoliths
CSIRO has patented a technology for forming carbon materials into porous monolithic type structures. This project explores the possibility of adapting this technology to H2 compression and storage applications
For more information contact Dr Ashleigh Cousins