Carbon nanotubes fuel thermowave power

Massachusetts Institute of Technology (MIT) researchers are utilizing fuel-coated carbon nanotubes as "fuses" for thermowave electrical power sources, which store energy like a battery but promise an unlimited shelf life. Thermowave power ignites its fuel to produce electricity through a newly discovered technique that combines nanotechnology with combustion waves, a phenomenon discovered more than a century ago.

"Unlike a battery or super capacitor, there is zero self-discharge with this approach, plus it works well for powering small things, since the power density is very large," said MIT professor Michael Strano. "Disposable medical diagnostics, transponders, beacons and signals, rockets and projectiles, and low-current-draw applications, which would normally require a small battery, could benefit from such devices."

"Its power density is very high"—potentially 100x greater than that of Li-ion batteries," said Strano, who performed the work with MIT doctoral candidate Wonjoon Choi.

In a process much like lighting a dynamite fuse, igniting one end of a fuel-coated nanotube causes a burn down its length that simultaneously produces enough electrical current to be used as power.

Combustion waves have been a theoretical curiosity for more than a hundred years, but Strano claims to be the first researcher to recognize that they also produce electrical current. He also claims to be the first to demonstrate that carbon nanotubes can be used to guide the combustion wave down the path of a conductor, thereby pushing an electrical current along with it.

Normal themoelectric theory cannot be used to model the phenomenon, according to Strano. He coined the term electron entrainment and produced a set of equations to describe the effect, in which current is proportional to the thermal wave velocity.

For the future, Strano is experimenting with different fuels, such as ethanol, in hopes of producing a more efficient fuel cell with a higher power density. He is also experimenting with using alternating bands of different types of reactants in hopes of learning how to directly produce alternating current using the technique.

"With additional engineering, you could see new types of fuel cells and electronic power supplies that use this thermopower wave concept," said Strano.

The Air Force Office of Scientific Research and the National Science Foundation provided funding for the project.

- R. Colin Johnson
EE Times