As body-worn and implanted medical devices are continuing to proliferate, the need to utilize power from something other than batteries increases. Researchers from Huazhong University of Science and Technology developed a wearable flexible device that can produce electricity from body heat.
The device relies on two gel electrolytes, allowing the final device to be flexible and produce as much as 0.7 volts and 0.3 µW. Since the system works using the thermogalvanic effect, the higher the difference between the body temperature and the environment, the greater the voltage. While above numbers are pretty impressive and sufficient to power a lot of potential devices, they were produced when the environment was only five degrees above freezing, way too cold for most applications.
From the announcement by Wiley:
The ions of a redox pair in the electrolyte can rapidly switch between two different charge states, accepting or releasing electrons at electrodes with different temperature. In order to use this to produce a current, the scientists combined two types of cells containing two different redox pairs. Each cell consists of two tiny metal plates that act as electrodes, with an electrolyte gel in between. The first cell type contains the Fe2+/Fe3+ redox pair. The second type of cell contains the complex ions [Fe(CN)6]3−/[Fe(CN)6]4−. Because of the choice of these redox pairs, in cell type 1, the cold end gives a negative potential, while in type 2, the cold end gives a positive potential.