Empowering ultrahigh solar reflectivity in glass-ceramics through m-ZrO2 nanotwins for efficient building radiative cooling

Porous ceramic based radiative cooling materials offers an energy-efficient solution for buildings cooling. Yet inter-connected micropores in those materials not only weaken their mechanical strength and resistance to pollutant penetration, but also inhibit the compatibility with structural colors. Herein, ultra-high reflective SiO 2 -ZrO 2 glass-ceramics are prepared by introducing lamellar m-ZrO 2 nanotwins into SiO 2 matrix. m-ZrO 2 nanotwins are proven effective in enhancing the reflection of sunlight, which provides an alternative to the Mie scattering of pores. The glass-ceramics exhibit a solar reflectivity of 0.98 at a low porosity of 17.62%, while maintaining excellent mechanical properties. Based on self-assembly and an annealing process, long-range ordered SiO 2 microspheres arrays are deposited to the surface of the glass-ceramics, yielding structural colors and elevated reflectivity up to 0.99. The green structural colored glass-ceramics with highest reflectivity achieve 3.97 ℃ daytime cooling performance under solar irradiation of 672   W   m -2 . When used as the envelope of a typical four-story midrise apartment building, such glass-ceramics demonstrate cooling energy saving by at least 15% and the highest annual electricity cost saving of 44,136 CNY (6,199 USD) across 32 representative cities in China. The developed SiO 2 -ZrO 2 glass-ceramics hold tremendous potential for use in advanced radiative cooling, particularly of buildings.