A Flexible, Self‐Adhesive, and Waterproof MXene‐Based Composite Thermoelectric Film With a Brick‐and‐Mortar Structure for Advanced Temperature Sensing and Multifunctional Applications

ABSTRACT Flexible, self‐powered thermoelectric (TE) temperature sensors are essential for next‐generation human‐machine systems, yet their practical deployment is hampered by a persistent trade‐offs among high sensing performance, robust environmental stability, and scalable manufacturing. Here, we overcome these challenges by developing a flexible and self‐adhesive TE composite film through a scalable, all‐aqueous vacuum filtration of MXene, PEDOT:PSS, and waterborne polyurethane (WPU). This approach creates a unique “brick‐and‐mortar” nano‐architecture, where lamellar MXene nanosheets are cemented by a WPU matrix, conferring exceptional water impermeability and long‐term operational stability. Crucially, the electroactive bridging of MXene nanosheets by PEDOT:PSS establishes a uniform and efficient conductive network at an ultra‐low filler loading (3.3 wt%), supporting low‐cost manufacturing. Consequently, the resulting film delivers a compelling combination of universal self‐adhesion and high‐performance sensing, characterized by excellent temperature sensitivity, a rapid thermal response, and low electrical noise that enables a high resolution of 0.01 K, while maintaining stable operation even when submerged. This work offers a scalable strategy for high‐performance flexible TE sensors, enabling applications in intelligent material identification, underwater sensing, and human‐machine interaction.