3D printable thermoelectric ink turns car exhaust pipes into power generators

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A research team from the Ulsan National Institute of Science and Technology (UNIST) in Korea has developed a thermoelectric ink capable of producing power-generating tubes using 3D printing.

Made up of lead (Pb) and tellurium (Te), the power-generating tubes could form the basis of high-performance thermoelectric generators capable of generating electricity from waste heat from industrial or car exhaust gases.

The researchers believe their development offers a promising means of enhancing fuel energy efficiencies, and leveraged 3D printing as a means of overcoming the challenges associated with conventional methods of manufacturing thermoelectric materials, such as limited design flexibility.

"Through this research, we will be able to effectively convert heat generated by factory chimneys, the most common type of waste heat source, into electricity," said Professor Jae Sung Son of UNIST's Department of Materials Science and Engineering.

The rise of thermoelectric technologies

Global energy demand has increased significantly in recent times due to an increased global population and the improvement in living standards in developing countries. According to the research paper, more than 80 percent of the current global energy consumption is enabled by fossil fuel sources, while over half of the heat energy generated by nature and human-made settings is simply dissipated into the surrounding environment.

To address this, thermoelectric power generation could provide a reliable and more environmentally-friendly method for waste heat recovery. Thermoelectric modules should, the researchers say, be designed specifically for individual systems for efficient heat transfer, while having a simple system and low processing cost. However, typical manufacturing processes to produce such modules do not fulfill these requirements, especially for exhaust pipes.

This realization led the UNIST team to turn to 3D printing, upon which they successfully designed and produced high-performance power-generating thermoelectric tubes that can be customized for integration with different thermal systems and to allow for geothermal adjustments.

3D printing thermoelectric power generators

During their study, the UNIST team leveraged an extrusion-based 3D printing process for PbTe materials and designed a power-generating thermoelectric tube with customized PbTe ‘legs’. They then developed an impurity-free PbTe ink with viscoelasticity to make it suitable for 3D printing, and induced strong surface charges in the particles within the ink via ‘electronic doping’.

The researchers 3D printed the PbTe ink into tube-like shapes which were then assembled to form a self-sustaining power-generating thermoelectric tube. According to the researchers, the competitive thermoelectric properties and printability of the PbTe materials enabled the design of free-form 3D printed thermoelectric modules beyond the limitations of conventional structures.

The tubes demonstrated high thermoelectric performance at temperatures between 400 and 800 degrees Celsius, which is the temperature range of a car's exhaust gases. The tube shape also made the thermoelectric generator more effective in collecting heat than a conventional cuboid type.

The 3D printed thermoelectric tubes could therefore be utilized directly as exhaust pipes through which hot fluids flow, the team claims, and form the basis of a skeleton-type design of a light, simple thermoelectric generator system. The design reportedly provides the "most effective means for heat transfer" from high-temperature fluid flow through a tube to a thermoelectric generator, as there are no thermal resistant layers between the fluid and the thermoelectric ‘legs’, such as a ceramic substrate in a conventional thermoelectric generator made of ferrous alloys.

The team believes their approach offers great potential for cost-effective processing to design high-performance customizable thermoelectric modules, and in order to industrialize the technology will look to overcome the issue of corrosion caused by exhaust gases. The development of anticorrosive coating technologies for thermoelectric materials will help to negate this issue, and there is already work underway in this field.

"If we use 3D printing technology in the production of thermoelectric materials, we will be able to overcome limits of conventional materials," said Professor Han Gi Chae of UNIST's Department of Materials Science and Engineering. "The new technology for providing viscoelastic characteristics to 3D printed materials will be used in various other sectors."

Further information can be found in the study titled: "Doping-induced viscoelasticity in PbTe thermoelectric inks for 3D printing of power-generating tubes," published in the Advanced Energy Materials journal. The study is co-authored by J. Lee, S. Choo, H. Ju, J. Hong, S. Eun Yang, F. Kim, D. Hwi Gu, J. Jang, G. Kim, S. Ahn, J. Eun Lee, S. You Kim, H. Gi Chae, and J. Sung Son.

Improving power efficiencies with 3D printing

3D printing technologies have also been leveraged elsewhere to regulate and improve the thermal and electrical efficiencies of a range of industrial components.

For instance, ceramic specialist CeramTec has tested the cooling capabilities of its new e-mobility-focused power semiconductor module, developed in partnership with Fraunhofer IISB, which is designed to thermally regulate the drive inverters of EVs. The module reportedly harbors twice the thermal resistance of conventional heat management systems while demonstrating an increased heat transfer surface.

Meanwhile, 3D Systems has been selected by aerospace firm Raytheon Technologies and the Army Research Laboratory's CCDC to develop topologically optimized heat exchangers for the US army via additive manufacturing. The partners will design, manufacture and optimize a component capable of maximizing the cooling and system performance of various army modernization products.

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Featured image shows A) The entire measurement set-up and B) The TEG mounted with cooler and connected to measurement electronics. Image via UNIST.

Hayley is a Technology Journalist for 3DPI and has a background in B2B publications spanning manufacturing, tools and cycling. Writing news and features, she holds a keen interest in emerging technologies which are impacting the world we live in.