In this time-lapse series of photos, progressing from top to bottom, a coating of sucrose (ordinary sugar) over a wire made of carbon nanotubes is lit at the left end, and burns from one end to the other. As it heats the wire, it drives a wave of electrons along with it, thus converting the heat into electricity. Credit: Courtesy of the researchers
The batteries that power smartphones,computers and electric cars, are mostly made of toxic materials such as lithium that can be difficult to dispose of and have limited global supplies. Now, researchers have come up with an alternative system for generating electricity, which harnesses heat and uses no metals or toxic materials.
The new approach is based on a discovery in 2010 by Prof Michael Strano in Chemical Engineering, MIT. A wire made from carbon nanotubes can produce an electrical current when it is progressively heated from one end to the other, for example by coating it with a combustible material and then lighting one end to let it burn like a fuse. Strano and his team have increased the efficiency of the process >1000X and have produced devices that can put out power that is, pound for pound, in the same ballpark as what is produced by today’s best batteries but it could take several years to develop it into a commercializable product.
MOA: A pulse of heat pushes electrons through the bundle of CNTs, carrying the electrons with it like a bunch of surfers riding a wave. Sometimes the wave of heat produces a single voltage, but sometimes it produces 2 different voltage regions at the same time. “Our mathematical model can describe why that occurs,” Strano says, whereas alternative theories cannot account for this. According to the team’s theory, the thermopower wave “divides into 2 different components,” which sometimes reinforce one another and sometimes counter each other.
The new work uses sucrose ie table sugar. But the team believes that other combustion materials have the potential to generate even higher efficiencies. Unlike other technologies, the CNT-based power system works just on heat, so as better heat sources are developed they could simply be swapped into a system to improve its performance.
Already it can power an LED light. And unlike batteries that can gradually lose power if they are stored for long periods, the new system should have a virtually indefinite shelf life. That could make it suitable for uses such as a deep-space probe that remains dormant for many years as it travels to a distant planet and then needs a quick burst of power to send back data when it reaches its destination. It is also very scalable for use in the increasingly tiny wearable devices. Batteries and fuel cells have limitations that make it difficult to shrink them to tiny sizes, Mahajan says, whereas this system “can scale down to very small limits.” http://news.mit.edu/2016/mit-develops-nontoxic-way-generating-portable-power
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