Body Heat as a Source of Power For Wearable Electronics

body heat

Textiles integrated with electronics have become extremely popular providing sleeves enhanced with smartphone displays or sensors built into athletic wear. There has been a problem with these items, however, since the power sources that go along with them aren’t exactly comfortable. Chinese scientists have found a solution to this problem in the form of 2 gel electrolytes that use body heat as the source of energy.

Our bodies are able to make constant heat due to our metabolisms and our activity levels. Some of this heat from the skin is released into the environment but since there is only a small difference in temperature between skin and the temperature found in our surroundings, it’s not exactly easy to make body heat work for us effectively. In the past, thermal electric generators weren’t able to produce enough energy, were too brittle to act as a wearable system and were quite expensive. As well, electrolyte solutions such as thermocells cannot easily be integrated into wearable systems. Fortunately, a solution has been found by Huazhong University of Science and Technology‘s Jun Zhou, who led a team of researchers towards thermocells with electrolytes that are gel-based.

The researchers have been working with 2 electrodes that make contact with electrolyte gel or an electrolyte solution. They both remain at a different temperature in order to generate a potential difference. The electrolyte contains a redox pair with ions that can switch rapidly between 2 various charging states, releasing or accepting the electrons or the electrodes at a different temperature. The current was produced by the researchers using two cell types with different pairs of redox in them.

body heat power source
Body heat used as a power source. (Image credits : Wiley Online)

There are two small metal plates inside each cell and between them is an electrolyte gel. The redox pair Fe2+/Fe3+ lives inside the first type of cell while [Fe(CN)6]3-/[Fe(CN)6]4- ions can be found in the second cell type. The cool end in the first cell provides a negative potential while the cool end in the second cell offers a positive potential.

Many of the 2 cell types were placed in a checkerboard pattern with the cells interconnected by metal plates running below and above them in alternating sequence so they could be linked as a series. This checkerboard pattern was then integrated into a glove and when worn this glove produces a temperature difference between the lower and upper plates. A voltage is created between the neighboring cells, which adds up and can generate the current necessary to charge a battery or to give a device power.

In a 5°C environment approximately 0.3 μW and .7 volts were produced. It’s only a matter now of optimizing this cell system to generate more power using smaller gradients of temperature.

The full study was published in the journal Angewandte Chemie.