Aramid Aerogel‐Hydrogel Heterostructures for Flexible Convective Thermal Diodes

ABSTRACT Thermal rectification is critically essential for flexible electronics, wearable devices and intelligent thermal management. However, state‐of‐the‐art thermal diodes are severely restricted by insufficient mechanical conformability or limited rectification efficiency. Herein, we propose a flexible convective thermal diode (FCTD) constructed from aramid aerogel‐hydrogel heterostructures with asymmetric wettability. The positive terminal adopts polyvinyl alcohol/lithium chloride modified hygroscopic aramid hydrogel. Before encapsulation, it absorbs ambient moisture and then serves as a sealed internal water reservoir during operation. The negative terminal employs channelized hydrophobic aramid aerogel, which simultaneously realizes low thermal conductivity and ultralow‐adhesion vapor/condensate transport. This asymmetric wetting architecture establishes efficient evaporation‐condensation convection and high heat flux in the forward mode, while suppressing heat conduction in the reverse mode. The optimized FCTD achieves an exceptional thermal rectification ratio of 11.49 ± 0.35 under identical forward and reverse surface temperature boundaries of 90°C and 20°C, with a bending radius of 4.2 mm and stable rectification over 50 cycles. Numerical simulations further reveal the intrinsic asymmetric heat and mass transfer mechanism. This work provides a structural strategy for high‐performance flexible thermal diodes, and offers feasible guidance for the design of next‐generation intelligent thermal management systems.