Body heat as a power source

1 min read

Chinese scientists from Huazhong University of Science and Technology have created a flexible, wearable thermocell based on two different gel electrolytes which can harness the energy from body heat to power wearable electronics. In an environment at 5°C, it was possible to produce 0.7V and 0.3mW.

According to the researchers, because of the small temperature difference between skin (approximately 32°C) and the temperature of our surroundings, it is difficult to make use of body heat. Previous thermoelectric generators, such as those based on semiconductors, produce too little energy, are costly, or are too brittle for use in wearable systems. Thermocells with electrolyte solutions are difficult to integrate into extensive wearable electronics.

The team found a solution to this problem by using thermocells with gel-based electrolytes.

The scientists combined two types of cells containing two different redox pairs. Each cell consists of two 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-. In cell type 1, the cold end gives a negative potential, while in type 2, the cold end gives a positive potential.

The researchers arranged these two types of cells into a checkerboard pattern. The cells were connected to each other by a series of metal plates alternating above and below. 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 neighbouring cells, which makes it possible to generate current to power a device or charge a battery.