Sekisui Chemical Co Ltd started to test a temperature difference power generation sheet that uses a special thermoelectric conversion material and can be attached to a chimney.
Sekisui Chemical developed the thermoelectric conversion material in collaboration with Nara Institute of Science and Technology (NAIST). Based on carbon nanotube (CNT), it is more flexible and has a higher environmental affinity than conventional materials. It is expected to be attached mainly to heat sources such as air-conditioning piping.
Thermoelectric conversion occurs because of Seebeck effect, a phenomenon in which a voltage is generated by applying a temperature difference to a semiconductor. In general, CNT is a p-type semiconductor and cannot be easily made as an n-type semiconductor with a simple method. The newly-developed method uses NaCl (sodium chloride) and crown ether to structure sodium ions on the CNT, enabling to produce a stable n-type semiconductor.
Conventional power generation devices using a bismuth/tellurium-based thermoelectric material have been used in a limited number of places such as manufacturing plants because they contain a toxic material and cannot be easily disposed. Also, they are heavy and inflexible.
On the other hand, the CNT-based thermoelectric material can solve those issues. And they can be used for various purposes as long as there is a heat source that produces a temperature difference of about 40°C.
A prototype of the power generation sheet was made by arraying CNTs for unwoven cloths on a substrate. It is as large as a business card and can generate up to 475μW of electricity. It is flexible enough to be wrapped around a 5cm-diameter pipe. Sekisui Chemical plans to further reduce the thickness so that the sheet can be attached even to three-dimensional complex surfaces.