Carbon nanotubes, pictured here as hollow tubes made of carbon atoms in a chicken wire-like lattice, can generate energy when coated in fuel and lit like a fuse.
SYDNEY: Carbon nanotubes can generate energy when coated in fuel and lit like a fuse, and could potentially power a range of nanodevices from 'smart dust' to medical nanorobots.
By coating carbon nanotubes, which are hollow tubes made of carbon atoms in a lattice arrangement similar to chicken wire, in a highly flammable compound called nitrocelluose, a team of researchers were able to generate power three to four times greater than the best lithium-ion batteries, relative to the energy source size.
Nanodevices such as cardioverter-defibrillators the size of apple seeds or nanoscale systems that target cancer cells could potentially be powered by the new energy source. Microsensors known as 'smart dust' could be powered by carbon nanotubes to float in the air, collecting information about temperature, airborne pollutants and other characteristics.
"By coating a nanotube in fuel and igniting one end, we set off a combustion wave along it and learned that a nanotube is an excellent conductor of the heat from the burning fuel. Even better, the combustion wave creates a strong electric current," said co-authors Kourosh Kalantar-zadeh from the Royal Melbourne Institute of Technology (RMIT) and Michael Strano from the Massachusetts Institute of Technology in the U.S. of a report published in a recent issue of the Institute of Electrical and Electronics Engineers' Spectrum Magazine.
Carbon nanotube fuse
Creating a battery small enough to power nanodevices has posed a challenge to scientists for years. Thermopower waves appear to be the most probable way to produce such a battery, because a current is generated as a pulse (or wave) that is typically several milliseconds long.
The researchers were able to create a thermopower wave by burning one end of the carbon nanotube. This forged a high-speed heat wave which pushed electrons along the tube creating an electrical current.
There are some crucial properties needed for such a wave of electricity. The first is a large thermoelectric coefficient. The thermoelectric effect says that a material generates an electrical potential if there is a temperature difference between the two ends. If a material, such as carbon nanotubes, has a thermoelectric coefficient of one degree per volt, that means that there needs to be one degree of temperature difference between the two ends of the tube to produce one volt of electricity.
Electrical conductivity of carbon nanotubes allows the electrons to flow easily from one side to another without any resistance. The thermal conductivity of the material is also very important for a fuse, as a material with high thermal conductivity allows a flame to burn from one side to another without interference.
Kalantar-zadeh said that carbon nanotubes are the best material for this type of application. "Carbon nanotubes have a coefficient of 80-90 microvolts per degree and is also one of the most conductive material we can find. Also thermoconductivity is very high and it's the combination of the three," he said.
A wave of power
The combustion wave set off by the burning fuse travelled thousands of times faster along the nanotube than the fuel would whilst burning in open air. The researchers recorded a wave speed from 0.01 to 2 m per second. They've called it 'nanodynamite'.
"The funniest thing is the carbon nanotube remains intact," said Kalantar-zadeh. The nanodynamite is rechargeable, as the nanotubes are not destroyed during the reaction since the fuel is the only component being burned. The fuel-covered nanotubes are also very stable, and can be stored indefinitely, while conventional batteries may leak or erode over time.
A nanodevice needs a nanobattery
The researchers said that the fuel reaction needs to generate localised temperatures around 1,000 degrees Celsius to start a reaction that's fast enough to kick off the thermal wave. While this temperature seems extreme, they're confident that the nanotubes will be perfectly safe in almost any device, as heat is highly localised around the nanotubes, and contained within an area smaller than a cell.
The carbon nanotube fuel could reach commercial production within five years if the technology is picked up, the researchers added.
Materials chemist and device engineer Andrew Minett from the University of Sydney said the research is "an interesting approach" to the challenges of creating small-scale power sources. However, he highlighted that the challenge with carbon nanotube production is in creating a homogenous material, as nanotubes contain mixtures of both metallic and semi-conducting nanotubes. "So for every device the researchers make, potentially, one third of them will not propagate thermopower waves," he said.
Fonte: Cosmos
