High Pressure Hydrogen Storage in Carbon Nanotubes
Hydrogen storage for transportation is one of the most important problems faced in implementing a “hydrogen economy”. Hydrogen can be produced in many ways, but then must be stored for use by fuel cells. The U.S. Department of Energy’s Hydrogen, Fuel Cells & Infrastructure Technologies Program has set hydrogen storage goals to be achieved by 2015. New technologies and storage materials are required to meet these goals if a hydrogen economy is to be realized. The gravimetric capacity goal for hydrogen storage materials is set at nine weight percent hydrogen (net useful energy/max system mass). Experiments using carbon nanotubes, and other materials such as metal hydrides, metal organic frameworks and other carbon nanostructures have shown promise as hydrogen storage material, but not to the level required to meet DOE’s goals.
LLNL has developed an apparatus and method for high pressure hydrogen storage within multi-walled carbon nanotubes (MWCNT) exposed to ambient air pressure that promises to meet these goals.Description
The innovation exploits the inherent high elasticity and mechanical strength of single walled carbon nanotubes and the thick walled geometry of MWCNTs to absorb hydrogen at large weight percents required for long distance travel powered by fuel cells.
Hydrogen storage is accomplished by capping the ends of the MWCNTs—one end with a hydrogen permeable material and the other impermeable to hydrogen. The hydrogen permeable cap allows hydrogen to be charged thermally or using an electrolytic cell. Hydrogen release occurs through the same permeable cap by applying resistive heating.Benefits
The LLNL method of hydrogen storage in carbon nanotubes shows promise of 1 GPa storage pressure. This would provide approximately a factor of 2 increase in weight percent over current methods.More Information
A U.S. patent application has been filed for the method and apparatus.Technology Status
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