Printable graphite-based thermoelectric foam for flexible thermoelectric devices

Flexible thermoelectric materials are primarily composed of organic thermoelectric materials, which suffer from issues such as instability and poor conductivity. To overcome these limitations, this study aims to develop a cost-effective thermoelectric material by utilizing graphite and hydroxypropyl methylcellulose as raw materials. Through a mechanical foaming process, a graphite-based foam with a porous structure is fabricated. The obtained foam exhibits a Seebeck coefficient of approximately 32 μV K⁻¹ and a power factor of around 0.013 μW m⁻¹ K². Following an analysis of the microstructural morphology, the foam samples are subjected to compression treatment to convert the 3D foam into a porous film and thereby enhance the power generation efficiency of the thermoelectric material. Notably, the Seebeck coefficient of the compressed sample is 41 μV K⁻¹, and its power factor is approximately 6.7 μW m⁻¹ K². Furthermore, owing to the high plasticity of the foam slurry prior to molding, it can be used to fabricate thermoelectric devices through printing techniques. By employing this approach, a thermoelectric device consisting of nine individual p-type graphite thermoelectric units is printed on the A4 paper. The device produces a temperature difference of 32 K and a thermoelectric potential of 10 mV on a 373 K heating plate. Since both the sample and the paper are flexible, the device can be folded to reduce its size, which broadens the range of potential applications of these thermoelectric materials.