Researchers from the University of Massachusetts, Amherst, have developed a new method of harvesting electricity from body heat to power wearable devices. “The new, wearable thermoelectric generator is also sourced from non-toxic and non-allergenic substances, making it a viable candidate for wearable technology,” reports IEEE Spectrum. Furthermore, “the substrate on which the generator is built is plain old cotton fabric.” From the report: More precisely, it’s a vapor-deposited strip of cotton fabric — coated with a material called, brace yourself, “persistently p-doped poly(3,4-ethylenedioxythiophene)” a.k.a. PEDOT-Cl. One end of the fabric touches a person’s skin and is thus at a person’s body temperature. The other end, ideally, is exposed to the open air. The greater the difference in temperature between the two ends, the greater the electrical output. […] The innovation here was to vapor deposit their polymer only onto the surface of the cotton fibers — and not soak the entire cloth in the polymer.
By keeping the semiconducting material on the surface, they could allow for charge to flow through the material while still thermally insulating one end of the generator from the other. This stems from the competing demands of a good thermoelectric conductor. The ideal material must somehow keep one side hot and the other side cold — in other words, the material must be thermally insulating. However, it must at the same time conduct electrons. Electrical current needs to flow, or it’s not a very good generator. With this vapor deposition trick, she says, “The polymer can be really, really electrically conductive.” And PEDOT-Cl fills that bill. However, because the polymer is only coated on the outer surface of the cotton fibers, the bulk of the material (i.e. the cotton) is still able to perform its thermally insulating role. The research has been published in the journal Advanced Materials Technologies.
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