Three-Dimensionally Penetrated Inorganic Semiconductor/Carbon Nanotube Hybrids for Robust Thermoelectric Filaments

Directly mixing or coating inorganic semiconductors with fibrous nanomaterials offers a route to flexible thermoelectric filaments (TEFs), but this approach usually results in nanocomposites with low electrical conductivity, high thermal conductivity, and compromised mechanical flexibility. Here, a strategy to create a 3D penetration network of inorganic semiconductors within carbon nanotube filaments (CNTFs) is developed, resulting in high zT and mechanical stability. Highly porous hydroxylated CNTFs (HCNTFs) formed by hydrogen peroxide treatment allow the radial penetration of bismuth telluride nanoparticles into HCNTFs via dip-coating. The 3D penetration network of inorganic semiconductors within HCNTFs does not deteriorate carrier transport but suppresses thermal transport due to abundant nanograins and mesopores in hybrid TEFs. The thermal conductivity remains low (≈1-2 W m^-1 K^-1), comparable to pure bismuth telluride, while the power factor doubles compared to conventional coated samples, resulting in one order of magnitude higher zT values (up to 0.34 for p-type and 0.14 for n-type at 303 K), making it one of the best CNT-based hybrid TE materials. It exhibits outstanding flexibility and stability without delamination after 2000 bending cycles. A 3D flexible TE textile, fabricated by embroidering p-n segmented TEFs into knitted fabric, demonstrates potential applications for a remote fire alarm system.