Multifunctional Carbon Nanotube Based Thermoelectric Yarn Enabling Fire Warning and Waste Heat Harvesting

Abstract Thermoelectric (TE) fibers exhibit immense potential for flexible sensing and distributed energy harvesting. However, their practical deployment is constrained by intricate fabrication processes and limited durability. This work reports a high‐performance wearable TE fiber based on carbon nanotube. Fabricate via a combined chemical modification and mechanical twisting process, this fiber possesses excellent flexibility, weavability, and outstanding TE performance (maximum power factor PF max = 953 µW m −1 K − 2 ). When woven into firefighting suits, the fiber demonstrates exceptional stability across a broad temperature range, particularly in high‐temperature regions (≥500 K), along with rapid response characteristics (threshold voltage: 2 mV; response time: ≤0.5 s), rivaling many state‐of‐the‐art inorganic material‐based systems. Furthermore, when integrate with radiative cooling technology for harvesting human body waste heat, it achieves a power density of ≈0.98 µW cm − 2 . This performance surpasses the upper limits of most existing fiber‐based TE devices and approaches the advanced level of inorganic bulk‐based flexible devices, highlighting its broad application potential.