Effect of Humidity on Thermoelectric Performance of Polyaniline/Carbon Nanotube Composite Films

Owing to their capability for direct heat-to-electricity conversion and desirable flexibility, conducting polymer/carbon nanotube thermoelectric composites have garnered growing research interest and made substantial progress in recent years. However, high environmental stability—particularly under high-humidity conditions—is highly desired for their practical applications; there remains a paucity of research on the humidity responsiveness of their thermoelectric properties. Here, high-performance, free-standing, and flexible polyaniline (PANI)/single-walled carbon nanotube (SWCNT) composite films are developed, exhibiting a large power factor of (226.4 ± 16.2) μW/(m·K 2 ) at room temperature, which further reaches (309.3 ± 15.7) μW/(m·K 2 ) at 450 K. The stability of their thermoelectric performance and the underlying influencing mechanisms is systematically investigated under various environmental conditions (mechanical deformation, air exposure, and humidity), with a particular focus on high-humidity environments. Consequently, the as-prepared PANI/SWCNT composite films not only maintain stable thermoelectric performance against multiple mechanical rolling cycles but also demonstrate excellent long-term humidity stability even after prolonged humidity treatment (at 35 °C and relative humidity of 80% for 14 d). The superior humidity stability arises from 3 aspects: strengthened interfacial interactions between PANI and SWCNT via optimized doping/dedoping treatments; a unique lamellar void architecture that obviously reduces water vapor permeability; and a dense layered structure with improved surface smoothness induced by cold pressing, which effectively blocks water penetration. This study contributes to understanding the service stability of polymer-based thermoelectric composites in complex environments, thereby facilitating their practical application.