Free‐Standing, Multifunctional Thermoelectric and Acoustic Absorbing Nanocomposite Foams

Thermoelectric materials are potential energy harvesting technologies that enable direct, clean conversion between thermal and electrical energy. The efficacy of thermoelectric energy conversion is influenced by the electrical conductivity, thermal conductivity, and Seebeck coefficient. Flexibility, manufacturability, and cost‐effectiveness are also important factors. Polymeric nanocomposites offer advantages in these respects. However, the development of conductive‐polymer thermoelectric materials is limited to an in‐plane architecture, which does not resemble common real‐world scenarios. Moreover, existing works have low thermoelectric properties or rely on additives for performance improvement. In this work, a free‐standing thermoelectric nanocomposite foam is fabricated via the integration of thermally activated microspheres. Due to the microstructure, a thermal conductivity as low as 0.03 W m−1 K−1 is achieved, which is lower than reported for aerogels fabricated via freeze‐drying methods. Additionally, the nanocomposite foam can reach a maximum electrical conductivity of 1.13 S cm−1, power factor of 0.12 µW m−1 K−2, and thermoelectric figure of merit of 3.0 × 10−4. The study also evaluated the compressive stiffness and demonstrated the potential for sound absorption. With the unique combination of the thermoelectric, sound absorption, and mechanical behavior, these nanocomposite foams would offer versatile solutions to address the next generation energy harvesting and acoustic absorption applications. A free‐standing thermoelectric (TE) nanocomposite foam is created by utilizing thermally expandable microspheres in combination with carbon nanotube (CNT) and thermoplastic polyurethane (TPU). The polymer co‐precipitation process successfully integrated the microspheres with the nanofillers, forming a stable conductive network. The nanocomposite foam exhibits a low thermal conductivity between 0.03 to 0.12 W m⁻¹ K⁻¹, similar to aerogels. The nanocomposite foam also achieved a performance of figure of merit (zT) = 3.0 × 10⁻⁴ and power factor (PF) = 0.12 µW m⁻¹ K⁻2.