Generating energy using human body temperature and motions

Professor Won-joon Choi’s research team has developed a next-generation 

hybrid energy-generating device. 

The paper has been selected for the cover of the world's leading energy journal, 

ACS Energy Letters.

▲ Researcher Byung-seok Seo (first author), Researcher Young-sun Cha (first author), Professor Won-joon Choi (corresponding author), and Researcher Sang-tae Kim from KIST (corresponding author)

Professor Won-joon Choi and his team at the School of Mechanical Engineering, College of Engineering, Korea University, in collaboration with Sang-tae Kim, a researcher at the Center for Electronic Materials, Korea Institute of Science and Technology (KIST), have developed a next-generation hybrid device that generates energy using human body temperature and motions.

* Article title: Rational Design for Optimizing Hybrid Thermo-triboelectric Generators Targeting Human Activities (This paper has been selected for the cover of the ACS Energy Letters, IF=16.331, offline publication of September issue.)

* Authors: Professor Won-joon Choi, School of Mechanical Engineering, College of Engineering, Korea University (corresponding author); Sang-tae Kim, Center for Electronic Materials, KIST (corresponding author); Byung-seok Seo (first author); and Young-sun Cha (first author)

The paper has been selected for the cover of the world's leading energy journal, ACS Energy Letters, September issue.

In energy harvesting technology, energy dissipated during our everyday lives such as solar heat or human movement is collected and converted into electric energy. Such energy is mainly used to supply power, especially as an auxiliary power source for mobile devices or in environments where battery replacement is not easy. In order to increase the power generation performance and efficiency of energy harvesting devices, researchers have focused on studying hybrid devices that apply different power generation mechanisms to a single device. However, it was not easy to guarantee the efficiency of energy generation for hybrid devices, because they generate electrical energy from different energy sources.

In particular, for thermoelectric power generation via temperature differences, and triboelectric power generation via mechanical friction of different materials, it is very difficult to achieve optimal energy generation efficiency for both mechanisms in terms of the frequency at which the energy source is supplied.

Thus, previous studies have faced limitations in achieving optimal energy generation because they were conducted by simply combining different mechanisms into a single device.

Accordingly, Professor Choi’s research team has designed a thermoelectric + electrostatic harvesting device that uses human skin (temperature + movement) as an energy source to simultaneously harvest thermal energy - the energy source of thermoelectric power, and mechanical friction - the energy source of electrostatic power generation. The team has also presented a design strategy to optimize the energy efficiency of the device depending on the external environment.

The device is based on bismuth telluride (Bi2Te3), which has excellent thermoelectric properties in the body temperature range, and polydimethylsiloxane (PDMS), which has excellent electrostatic properties when in contact with human skin.

When human skin contacts the surface of the device, thermoelectric power is generated, as the human body temperature supplies thermal energy, while electrostatic power is generated due to the large difference in electron affinity between human skin and the device.

For thermoelectric power generation, thermal saturation occurs within the device when the contact duration is extended, and induces multiple effects on the efficiency of energy generation. Thus, the frequency is very important because it directly determines the amount of energy generated based on contact duration. For electrostatic power generation, the amount of energy generation increases as the frequency increases.

The team has focused on the thermal insulation properties that block the heat transfer of PDMS when used as a material for electrostatic generation, and has established an optimized design strategy for thermoelectric and electrostatic generation by analyzing the heat and electron transfer properties at the interface between the Bi2Te3 and PDMS, and by controlling thermal propagation within the device.

Based on these findings, the team has presented an optimal design strategy for a device that can generate the most energy for a frequency range of 0.5 Hz to 2.5 Hz.

Such research on an optimal design for energy generation is expected to help harvesting devices serve as a power source for Internet of things (IoT) devices and mobile electronic devices that require high energy output under limited spatial conditions.

<Schematic diagram of thermoelectric and electrostatic hybrid harvesting device generating energy 

at different frequencies of finger touch>