Impact of Air Temperature and Humidity on Performance of Heat-Source-Free Water-Floating Single-Walled Carbon Nanotube Thermoelectric Generators for IoT Sensors

Thermoelectric generators (TEGs), which can generate electricity simply by floating in water, have high potential for application as power supplies of IoT sensors. However, few studies on single-wall carbon nanotube (SWCNT)-TEGs have examined the effects of the power generation environment. Therefore, we investigated the impact of the relative humidity and temperature on the TEG performance. The SWCNT-TEGs were measured in environments with air temperature controlled at 25-40 °C and relative humidity controlled at 50-90%. Evaporative cooling occurs under environmental conditions with lower relative humidity and higher temperatures, resulting in higher output voltages. The SWCNT-TEG output voltage at 50% relative humidity and 40 °C was 0.26 mV, which was approximately 1.6 times higher than that measured at the same relative humidity and 30 °C, and approximately 1.4 times higher than that measured at 80% relative humidity and the same temperature, because a lower relative humidity and higher temperature increase the amount of water vapor in the air. This facilitates evaporative cooling, increasing the temperature difference within the film, thus increasing the output voltage. These results suggest that environmental factors have a significant impact on the SWCNT-TEGs and that power generation performance can be enhanced through effective use of evaporative cooling.