"Body Temperature as an Energy Source" KAIST Develops Wearable Thermoelectric Device

A wearable thermoelectric generator combining elasticity and high performance has been developed. Thermoelectric generators attract attention as eco-friendly and sustainable energy platforms because they convert thermal energy into electricity, utilizing waste heat. The developed technology is a wearable device using body temperature, and it is expected to serve as a core technology for implementing next-generation energy supply platforms.

Professor Moon Hongchul (left), Department of Bio and Chemical Engineering, KAIST, and Professor Park Taeho (right), Department of Chemical Engineering, POSTECH. Provided by KAIST

KAIST announced on the 14th that Professor Moon Hongcheol's team from the Department of Bio and Chemical Engineering and Professor Park Taeho's team from the Department of Chemical Engineering at POSTECH have realized a technology that overcomes the performance limitations of existing N-type thermoelectric galvanic devices by controlling thermodynamic equilibrium.

Thermoelectric galvanic devices can be classified into 'N-type' and 'P-type' depending on the direction of electron flow. N-type, meaning negative, refers to electrons moving from a low temperature to a high temperature, while P-type, meaning positive, refers to electrons moving from a high temperature to a low temperature.

To maximize the performance of thermoelectric devices, integration of N-type and P-type devices is essential. However, research has mainly focused on P-type thermoelectric devices, resulting in relatively insufficient studies on N-type thermoelectric devices.

Moreover, N-type thermoelectric devices have lower performance compared to P-type, causing imbalance when implementing integrated devices and hindering performance maximization.

To address this, the joint research team developed a gel material capable of self-adjusting acidity (pH) and implemented a thermoelectric galvanic device, a type of ionic thermoelectric device using ions as the main charge carriers.

Using the developed gel material, they effectively controlled the thermodynamic equilibrium of the hydroquinone redox (oxidation-reduction) reaction, an electrochemical reaction used to convert thermal energy into electrical energy, thereby successfully inducing high-performance N-type thermoelectric device characteristics.

In particular, the gel material developed by the joint research team was designed based on reversible crosslinking bonds, achieving excellent elasticity of 1700% and over 99% self-healing performance within 20 minutes at room temperature.

Reflecting this, the N-type ionic thermoelectric device achieved a high thermopower of 4.29 mV K-1 while demonstrating a Carnot relative efficiency of 1.05% (the actual thermal conversion efficiency of the thermoelectric galvanic device compared to the ideal Carnot engine efficiency), emphasized the joint research team.

Ultimately, the device attached to the wrist successfully produced energy effectively by utilizing the temperature difference between the body’s maintained temperature and the surrounding environment.

Professor Moon Hongcheol said, “This research is significant in that it developed a technology overcoming the limitations of existing N-type ionic thermoelectric systems,” adding, “It is expected to accelerate the practical application of power systems using body temperature and become a key element technology for driving wearable devices.”