This artist's conception shows water molecules passing through the inside of a single-walled carbon nanotube. Carbon nanotubes have been used to create thermopower waves and electricity. Researchers at RMIT University in Melbourne have now improved upon this technology using different nanomaterials.
Credit: iStockphoto
SYDNEY: Using ceramic-based nanomaterials, such as aluminium oxide and terracotta, Australian researchers have converted heat from solid fuels into electrical energy via thermopower waves.
This new technology could enable microscopic power sources with unprecedented capacity, advancing visions of truly autonomous micro- and nanoelectronics, and enabling more sophisticated implantable bio-devices to aid in disease therapy.
"Tiny electronic devices powered by thermopower waves could apply large energies to targeted cancer cells inside the human body, enabling an exceptional level of precision in cancer treatment," said study supervisor Kourosh Kalantar-zadeh, an electrical engineer from RMIT University in Melbourne.
Building on carbon nanotubes
Exothermic chemical reactions from nitrocellulose - a highly flammable compound often used as a propellant - are coupled onto layers of thermoelectric materials to produce high intensity waves that sweep across the material, generating electricity.
Researchers at the Massachusetts Institute in Technology near Boston have previously demonstrated that chemically driven thermopower waves, guided through carbon nanotubes, are capable of producing specific power as large as seven kilowatts per kilogram.
"We identified certain limitation in this," said co-author of the study, Sumeet Walia, an electrical engineer at RMIT. "The voltage was quite low, and the nature of the voltage was not oscillating."
Higher voltage, alternating current
The key breakthrough in the Australian research, published in the journal Energy & Environmental Science, is the ability to produce an alternating current, something that has not yet been achieved with carbon nanotubes. Their method also increased the voltage output by nearly an order or magnitude.
"Our work demonstrates a new class of micro-power sources and shows it is possible to obtain alternating output signals with opposite polarities, which is crucial for developing alternating signal sources," said Walia.
Although there have been recent advances in lithium ion batteries, their specific power and energy densities are quite low, the researchers report.
Additionally, conventional batteries and fuel cells are only capable of producing direct current power, while alternating current sources are far more desirable for electronics.
"This is an important milestone towards making efficient thermopower wave systems for future industrial applications," said Walia.
Useful power
One future application is the development of a concept called 'smart dust' - micro-electromechanical systems that are networked wirelessly for sensing and receiving data, and could be used to for testing soil quality across large agricultural fields or water safety in reservoirs.
Moving away from the very small scale, the technology might also play a role in reducing battery sizes for things like cars and aeroplanes. These bulky batteries produce large power surges at ignition, but serve little purpose during the normal operation of the engine.
"We have developed a credit card sized battery in an effort to get rid of big batteries," said Walia. "It's also useful in energy storage applications because if you're discharging energy all the time it's a waste."
Improving stability
"If heat can propagate quickly from one end of a structure to another, like an explosion, it can sweep electrons and generate quick bursts of electricity," explained Kosta Ostrikov, a nanotechnologist with the CSIRO, Australia's national science organisation.
Ostrikov, who was not involved in the research, said the authors "found a simple combination of easy-to-make materials and substrates ... to show thermopower waves with alternating polarity and much higher output voltage than before".
Still, current stability in the system is quite poor, he said. "It still remains chaotic rather than nice sine-wave AC... [And] They require exothermic burning of chemicals, which makes it less environmentally benign than solar cells."
