"Is My Body a Battery Now?"... UNIST Develops Film Generator That Lights LED Using Body Heat

Sungyeon Jang’s Team Presents Universal Design Principles for High-Performance Ionic Thermoelectric Materials
Commercial LED Powered by Tiny Temperature Differences... Published in Adv. Funct. Mater.

A film-type generator capable of lighting up an LED bulb using a temperature difference of just 1.5°C between human body temperature and the surrounding air has been developed.

The research team led by Professor Sungyeon Jang from the Department of Energy and Chemical Engineering at UNIST has simultaneously developed the world’s highest-performing flexible p-type and n-type ionic thermoelectric materials.

Research team, (from left) Professor Sungyeon Jang, Researcher Donghu Kim (first author). Provided by UNIST

Thermoelectric materials are a type of material that can generate electricity from temperature differences inside and outside the material, functioning much like a generator. Among these, “ionic” thermoelectric materials generate electricity through the movement of ions. In p-type materials, cations move, while in n-type materials, anions are responsible for the movement. When a temperature difference occurs, ions migrate toward the cooler side, creating a voltage and allowing current to flow.

The thermoelectric performance index (ZTi) of the newly developed materials is 49.5 for the p-type and 32.2 for the n-type, marking the highest values ever reported for ionic thermoelectric materials. This represents a 70% improvement over the previous record. The higher the thermoelectric performance index, the more efficiently electricity can be generated even with small temperature differences.

The p-type material is based on a conductive polymer composite of PEDOT:PSS, while the n-type material is formed by adding copper chloride (CuCl₂) to the p-type material. In the p-type material, hydrogen ions (cations) move to generate electricity, whereas in the n-type material, chloride ions (anions) are responsible for the movement.

Both materials are lightweight and flexible due to their polymer-based nature, allowing generators to be fabricated in a film form.

In practice, a film-type generator module was created by connecting 10 pairs of the p-type and n-type materials in series. This module generated a high voltage of 1.03V for every 1°C temperature difference, and was able to light up an LED bulb with only a 1.5°C temperature difference. Additionally, it maintained over 95% of its performance for more than two months in indoor environments, demonstrating excellent long-term stability.

Film-type thermoelectric modules (top) fabricated using the developed thermoelectric materials and their actual operation (bottom).

The research team explained that they were able to develop these materials by utilizing a thermodynamic design approach to find the balance point between the concentration of ions and the ion diffusion coefficient within the material. While higher ion concentration and faster ion mobility increase the power generation efficiency of thermoelectric materials, an excessive number of ions can actually hinder the flow. The team systematically analyzed factors such as the concentration of additives (like copper chloride) that determine ion concentration, and the internal structure of the material (such as polymer aggregation) that affects the diffusion coefficient, ultimately identifying the point where the overall power density is maximized.

Donghu Kim, the first author of the study, explained, “Ionic thermoelectric materials have so far lacked systematic design guidelines, making it difficult to fully realize their potential performance. This study presents a design principle for these materials.”

Professor Sungyeon Jang stated, “The developed materials are thin and flexible, allowing them to easily adhere to the body or curved surfaces. They can be applied to the development of wearable smartwatches that charge without batteries, or self-powered sensors that operate in environments where the temperature difference between the inside and outside is only a few degrees to several tens of degrees Celsius.”

The research results were published online in the international journal Advanced Functional Materials on October 4. The research was supported by the National Research Foundation of Korea (NRF) under the Ministry of Science and ICT, and the InnoCORE project.

This content was produced with the assistance of AI translation services.