Biologically inspired shell-hollow particles for designing efficient passive all-sky radiative cooling

Passive radiation cooling (PRC), as the most promising technology to meet future cooling needs, has attracted great interest. However, there are still huge challenges in manufacturing high-efficiency and low-cost radiant coolers suitable for all-day use. Here, we report a secondary micro-nano shell-hollow structure based on blending method, inspired by the African white beetle Goliathus goliatus. Due to the difference in reflectance between the shell and the internal air, compared with the homogeneous particles, the scattered light has a changed optical path at the interface of the core (air) and the shell (SiO₂), and most of the light escapes from the particles, showing strong total internal reflection. The design ingeniously deposits the nano-sized shell-hollow structure on the surface of the micron-sized shell-hollow structure, achieving high solar reflectance (95 ​%)and excellent long-wave infrared emissivity (94 ​%). Sub-ambient cooling of 7.8 and 4.7 ​°C can be achieved at night and daytime, respectively. Silica microspheres with shell and hollow structure can be prepared by soft template method, which is mature, reliable, simple and cheap.Our work provides new ideas for the design and manufacture of high-performance Passive all-day radiative cooling (PARC).