8 July 2009

High capacity hydrogen storage in reverse

There is now a reversible route to generate aluminum hydride, a high capacity hydrogen storage material.

The development could accelerate the development of a whole class of storage materials, and it also has far reaching applications in areas spanning energy technology and synthetic chemistry.

“We believe our research has provided a feasible route to regenerate aluminum hydride, a high capacity hydrogen storage material,” said Dr. Ragaiy Zidan of the U.S. Department of Energy’s Savannah River National Laboratory (SRNL), lead researcher on the project.

The SRNL team developed a closed cycle for producing aluminum hydride, also known as alane, which potentially offers a cost-effective method of regenerating the hydrogen storing material in a way that allows it to repeatedly release and recharge its hydrogen.

In this process, researchers can make the hydride via an electrochemical method, and the starting material regenerates directly with hydrogen. In the past, researchers attempted to make alane electrochemically, however none were a success.

For years, a major obstacle in reaching the hydrogen economy has been hydrogen storage. Solid-state storage, using solid materials such as metals that absorb hydrogen and release it as needed, has safety and practicality advantages over storing hydrogen as a liquid or gas, and quite a few storage materials have undergone testing trying to meet DOE’s goals. Several materials have met or exceeded the DOE gravimetric and/or volumetric performance targets. Of those, however, the majority do not have the required thermodynamic and kinetic properties that allow them to release their hydrogen when needed. Also researchers can not efficiently and economically reload with hydrogen when spent.

Alane possesses the desired qualities, but there was a flaw. It seems the material required high pressures to combine hydrogen and aluminum to reform the hydride material. Alternate methods of production using chemical synthesis produced stable metal chloride byproducts that make it practically impossible to regenerate the alane. However, the electrochemical cycle demonstrated by Dr. Zidan and the SRNL team avoids both issues.

In addition, the SRNL team discovered novel ways to facilitate separation and formation of aluminum hydride that also apply to the formation of other complex metal hydrides and have the potential to cost-effectively regenerate other high capacity hydrogen storage materials. The SRNL results should accelerate the development of a whole class of similar materials needed for hydrogen, batteries, and other energy storage applications.

For related information, go to www.isa.org/manufacturing_automation.