Invention makes it possible to charge electronics in clothing via body heat

A team of Chinese researchers has devised a way to generate energy by taking advantage of the difference in temperature between the surface of the body and the outside air using gel-shaped electrolytes.

For example, portable electronics can be supplied with energy with the energy obtained from the body heat converted into electricity. The Chinese used two types of thermogalvanic gel electrolytes, one positive and one negative, which were placed between two flexible substrates. Thus, a gel-based thermocell could be made.

The use of gel electrolytes makes the Chinese technology for wearables more interesting than previous residual heat generators, which work with liquid electrolytes or salts as the electrolyte. The system functions by means of the thermogalvanic effect, where two electrodes are placed in a conductive liquid or electrolyte. Often an electrolyte consists of a liquid, but that is not useful in connection with leaks. That’s why the Chinese used a gel.

The gels are placed in separate cells, where the cell with Fe2+ and Fe3+ on the cold side of the cell has a negative potential and cell type two with [Fe(CN)6]3- and [Fe(CN)6]4- a positive charge on the cold side.

The cells are then arranged in a checkerboard pattern and connected alternately above and below with metal plates, so that the cells are in series. As a prototype, the researchers developed a glove that could produce 0.7V at 0.3μW in an environment of 5°C, which is very little. The expected return on these types of systems is also very small, but may not be very relevant depending on the type of application. The researchers’ first goal is in any case to obtain more energy from smaller temperature differences. The average temperature of the skin is about 32°C.

The article in Angewandte Chemie can be found at Wiley.