Gradient Porous and Carbon Black‐Integrated Cellulose Acetate Aerogel for Scalable Radiative Cooling

Passive temperature controls like passive daytime radiative cooling (PDRC)-heating (PDRH), and thermal insulation are essential to meet the growing demand for energy-efficient thermal solutions. When combined with advanced functions like electromagnetic interference shielding, these technologies can significantly enhance scalability. However, existing approaches using single thin films or uniform porous materials face inherent limitations in optimizing versatile functions, while lightweight, insulating aerogels can extend their multifunctionality by manipulating pores and fillers. Herein, carbon black (CB)-containing cellulose acetate (CA)aerogels (CB/CA aerogel) featuring gradient pores and bilayer structures are devised to implement switchable PDRC-PDRH and broadband spectral emissivity from infrared to microwave, along with high thermal insulation and elasticity. Using stirring and freeze-drying methods, the CA aerogels show low thermal conductivity (≈0.034 W mK^-1) and demonstrate broad-spectrum functionality, with over 95.7% solar reflectivity and 93% long-wavelength infrared (LWIR) emittance, achieving a 12.25 °C temperature reduction in outdoor conditions. Furthermore, the CB/CA aerogels enhance LWIR emittance to 98.7% and provide broadband spectral emissivity with 39.4% microwave absorption. This study offers a viable solution to simultaneously control radiative cooling and microwave absorption across a broad spectrum in porous media.