Asymmetric hierarchically structured composite aerogels with enhanced dual-spectral selectivity for efficient radiative cooling

Passive radiative cooling (PRC) has emerged as a promising zero-energy cooling technology for achieving global carbon neutrality goals. However, conventional PRC materials face persistent challenges including seasonal overcooling effects and limited cooling efficiency due to unavoidable solar absorption and thermal conduction losses. In this work, we develop an asymmetric PLA/SiO₂ composite aerogel with hierarchical porous structure through a facile water-induced phase separation strategy, where gravity-driven SiO₂ particle sedimentation creates enhanced dual-spectral selectivity on the aerogel's bottom surface. The composite aerogel integrates superior radiative cooling and thermal insulation functions in a single design, simultaneously achieving ∼97.1 % solar reflectance, ∼95.6 % atmospheric window emissivity, and ultralow thermal conductivity (0.032 W m⁻¹ K⁻¹). Outdoor measurements confirm effective cooling performance with temperature drops of ∼8.83 °C under direct sunlight and ∼5.66 °C in cloudy conditions. Moreover, the aerogel exhibits retained self-cleaning functionality and optical stability after various environmental durability tests, adapting to harsh real-world applications. Energy consumption simulations demonstrate that the aerogels have great potential of year-around energy saving and CO₂ reduction in China for energy-efficient building models integrated with aerogels on roof and walls. This study pioneers the creation of biodegradable PRC materials that combine building thermal management with environmental sustainability, thereby propelling the advancement of next-generation energy-efficient buildings.