Mail Online reports that a team led by Jun Zhou at Huazhong University of Science and Technology (Wuhan, China) has introduced a flexible, wearable thermocell based on two different gel electrolytes, based on their research that shows if two electrodes in contact with an electrolyte solution—or an electrolyte gel—are kept at different temperatures, a potential difference is generated.
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.
Dr. Jun Zhou deputy director of Wuhan National Laboratory for Optoelectronics at Huazhong University of Science and Technology in China who led the research, said: 'This technology could have an application in the future as a generator that uses body heat for powering functional electronics.' It could mean that wearable technology like smartwatches and fitness monitors could charge up while on your wrist by incorporating the gel into the straps.
The researchers arranged many of these two types of cells into a checkerboard pattern. The cells were connected to each other by metal plates alternating above and below, to link them into a series. They then integrated this "checkerboard" into a glove. When the glove is worn, the desired temperature difference results between the upper and lower plates. This produces a voltage between neighboring cells, and the voltage adds up. This makes it possible to generate current to power a device or charge a battery.
In an environment at 5 °C, it was possible to produce 0.7 volts and about 0.3 µW. By optimizing this system, it should be possible to improve the power, even with smaller temperature gradients.