Hierarchically structural TiO2-PVDF fiber film with particle-enhanced spectral performance for radiative sky cooling

Radiative sky cooling is a passive cooling method without consuming any additional energy. Here, we propose a kind of hierarchically structural and particle-enhanced TiO2-PVDF fiber film as the radiative sky cooling material. TiO2-PVDF fibers are prepared by the polymer assisted electrospinning technique. The hierarchical structure encompasses polymer fibers, inorganic enhanced particles and pores formed by interlacing fibers. In this work, the effect of TiO2 adding on the morphology, structure and spectral performance of hierarchically structural fiber film are discussed. By introducing the inorganic TiO2 particles with high refractive index into polymer fiber matrix, the refractive index difference among the hierarchical structure can increase the scattering and solar reflectance, and phonon polariton resonance will increase the infrared emission. The obtained TiO2-PVDF fiber film possesses the optimal high solar reflectivity of 99.01% (Vis band), 97.20% (NIR band) and infrared emissivity of 89.91% within the atmospheric window band. In outdoor testing in Wuhan (temperate climate) during October, the maximum sub-ambient cooling temperature under sunlight can reach 6.9℃, and 4.4℃ at night. Thus, this TiO2-PVDF fiber film can become a promising all-day cooling and energy saving material. Furthermore, it can be used in the more cooling and thermal management fields to greatly improve the comfortability of people's living and life.