n-Type PVP/SWCNT Composite Films with Improved Stability for Thermoelectric Power Generation

Single-walled carbon nanotubes (SWCNTs) are one of the promising thermoelectric materials in applications of powering wearable electronics. However, the electrical performance of n-type SWCNTs quickly decreases in air, showing a low stability, and low-cost and effective solutions to improving its stability are also lacking, all of which limit practical applications. In this study, we studied the stability of PVP/SWCNT composite films, where oxygen and moisture from air should be responsible for the decreased stability due to oxidation and hydration. In this case, we found that coating with a 0.20 g mL^-1 PVP/0.002 g mL^-1 PVDF layer on the surface of PVP/SWCNTs can prevent the penetration of oxygen and moisture from air, improving film stability, where there is almost no reduction in thermoelectric performance after they are exposed to air for 60 days. Based on the stable n-type PVP/SWCNT films, a thermoelectric generator was fabricated, where poly(dimethylsiloxane) (PDMS) was used to coat the surface of the thermoelectric leg to further improve its stability. This generator showed high output performance, which achieved an open-circuit voltage of 10.6 mV and a power density of 312.2 μW cm^-2 at a temperature difference of 50 K. Particularly, it exhibited high stability, where the output performance kept almost unchanged after exposure to high-humidity air for 30 days. This coating technology is also applicable to other air-sensitive materials and promotes the development and application of thermoelectric materials and devices.