Nature-Inspired Radial-Gradient Hierarchically Porous n-Type S-Doped Ag₂Se/Aramid Nanofiber Composite Thermoelectric...

N-type thick TE fibers remain an open question to obtain fibers with both high TE properties and flexibility for wearable applications. Moreover, traditional thermoelectric fibers rely on reducing thickness for a suppressed area moment of inertia for high flexibility, which will deteriorate the output performance. Herein, as inspired by the gradient structure in soft biological materials, we report a type of n-type composite TE fibers possessing radial gradient hierarchy through in situ growing S-doped Ag₂Se nanocrystals into wet-spun porous aramid nanofibers after ultrafast sintering. The coupling of gradient architecture and interfacial interaction between Ag₂Se and nanofibers imparts gradient fibers with a harmonious balance between TE performance and mechanical flexibility. We qualitatively elucidate that the role of radial gradient structure endows fibers with stress redistribution and energy absorbance toward improved flexibility. The optimal gradient fiber with tuned carrier and phonon transport exhibits a ZT of 0.42 at room temperature and a bending radius of 5 mm. Its TE fabric shows a normalized power of 82 μW m^-2 K^-2, enabling a high thermal resolution of 0.03 K for precise temperature sensing.