Dual-gradient radiative cooling aerogels with phase-change-coupled directional heat transport for adaptive thermal management

Abstract

Aerogels, featuring ultralow thermal conductivity and abundant micro/nanopores, hold great promise for radiative cooling by simultaneously suppressing non-radiative heat gain and enhancing solar scattering. However, in more complex thermal-management scenarios, their intrinsic thermal-insulating nature also hinders heat transfer from the interior to the cooling surface, thereby limiting net cooling output in enclosed or self-heating systems. Herein, we report a phase-change-functionalized radiative-cooling aerogel (GPSBA) fabricated by a multistage directional freeze-casting strategy, in which a cooperative gradient distribution of pore structure and boron nitride-coated phase-change microcapsules (BN@PCM) is established within a continuous anisotropic network. This design integrates radiative cooling, directional heat transport, and smart temperature response into a single material system. The optimized GPSBA exhibits a solar reflectance of 94.8% and an atmospheric-window emissivity of 96.4%, together with pronounced asymmetric heat-transfer behavior and a thermal rectification coefficient of up to 35%. In outdoor tests, GPSBA achieves a maximum daytime sub-ambient cooling of 14.9 °C and an average daytime sub-ambient cooling of 10.5 °C, while effectively alleviating nocturnal overcooling. More importantly, in sealed environments with internal heat sources, GPSBA provides an additional cooling effect of 4.3 °C compared with conventional aerogels. This work offers a promising design strategy for transforming radiative-cooling aerogels from static thermal barriers into adaptive materials for sustainable thermal management in dynamic environments.