Control of Liquid-Absorbing Structure to Improve Performance of Transpiration-Type Thermoelectric Power-Generating Device Using Carbon Nanotube Composite Paper

We propose an improved transpiration-type thermoelectric power-generating paper (t-TEPGP) with controlled water absorption. We have succeeded in developing t-TEPGP based on the carbon nanotube (CNT) composite paper (CNTCP). The CNTCP that was developed in our previous study is a composite material made from CNTs and pulp, enabling thermoelectric power generation due to its CNT content. Furthermore, CNTCP can spontaneously generate a temperature difference without requiring an external heat source, as it utilizes both the liquid absorption capacity via capillary action and the latent heat of vaporization released when the liquid evaporates. This study aimed to control the generated temperature gradient by partially modifying the internal structure of CNTCP during its manufacturing process-specifically, by altering its water absorption capacity through the choice of hot pressing or oven drying. Pressing was expected to reduce water absorption, while oven drying was predicted to increase it. Through multiple experiments, we confirmed that a sample spontaneously generated a maximum temperature difference of 0.6 °C due to evaporation heat, producing an electromotive force (E.M.F.) of 47 μV. This performance was approximately twice that of previous studies. Furthermore, we confirmed that a sample consisting of three pairs could generate an E.M.F. of 193 μV with a temperature difference of 1.2 °C.