Thermoelectric Properties of Authentic Aerogels Incorporating PEDOT:PSS with Mesoporous Structures Fabricated by Supercritical Drying

We focused on clarifying the structure, thermal and electric conducting properties, and thermoelectric (TE) properties of an authentic aerogel comprising poly(3,4-ethyrenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) that was fabricated via supercritical CO2 drying of an alcogel of cross-linked PEDOT:PSS. Most studies on porous organic TE materials have focused on cryogels with macroporous structures; few reports exist on authentic aerogels with mesoporous structures that exhibit TE effects. The fabricated PEDOT:PSS aerogel had a large surface area (300 m2 g–1) and mesopores (20–30 nm), which effectively restricted gas molecule convection, resulting in a low thermal conductivity of approximately 0.05 W m–1 K–1. Moreover, this unique structural integrity was retained up to nearly 300 °C. The conductivity was significantly enhanced by cross-linking treatment with divinyl sulfone (DVS) and methanol replacement prior to supercritical CO2 drying, yielding an effect similar to that of secondary doping. The treated PEDOT:PSS aerogel exhibited a negative temperature dependence on conductivity, which can be attributed to the band-like carrier conduction typically observed in degenerate semiconductors. The relationship between the conductivity and Seebeck coefficient as a function of the temperature is also consistent with the behavior of degenerate semiconductors. Consequently, the PEDOT:PSS aerogel can be regarded as a mesoporous TE material with low thermal conductivity and the characteristic properties of a degenerate semiconductor.