Temperature-arousing thermoelectric sensor based on oriented cellulose fibrils toward self-powered active fire protection

Rational structural design is crucial for enhancing thermal conversion efficiency and is therefore essential for advanced thermal-management applications. However, simultaneously achieving high electrical conductivity and low thermal conductivity in thermoelectric (TE) materials through oriented structural design remains a long-standing challenge. Herein, a PEDOT: PSS/MXene-based TE unit is fabricated via a top-down strategy using oriented wood cellulose fibrils as a natural scaffold. The inherent long-range alignment of cellulose fibrils enables the formation of a continuous, directionally conductive network that facilitates the rapid transport of thermally excited charge carriers, leading to remarkably high electrical conductivity. Meanwhile, the hierarchical micro/nanopores (0.1–50 μm) derived from the cellulose framework induce strong phonon scattering, resulting in ultralow thermal conductivity and pronounced temperature gradients under heat stimuli. Subsequently, the TE unit exhibits an excellent Seebeck coefficient (10.051 μV K −1 ), high electrical conductivity (1776 S m −1 ) at elevated temperatures, and a sufficiently low thermal conductivity (0.032 W m −1  K −1 ). When coupled in series with an n- type MXene unit, the resulting self-powered high-temperature warning device demonstrates a broad sensing range (100–400 °C) and a rapid thermal response (~1.3 s). This oriented structural framework, derived from rational design principles, offers scalability for integration with diverse thermal conversion composites, providing new insights into the design of advanced functional architectures for practical thermal management and self-powered sensing applications.