Abstract

Radiative cooling materials (RCMs) based on polymers, that reflect solar irradiance (0.24–2.5 µm) strongly and emit radiation within atmospheric window (8–13 µm) intensively, have yielded obviously cooling performance. However, RCMs reported failed to realize high mid-wave infrared (2.5–8 µm) reflectance (i.e., spectral selectivity), which play an importance role in reject the radiation from ambient especially in high relative humidity. Thus, enhancing the reflectance of RCMs in mid-wave infrared can further strengthen the cooling effect in the environment of high relative humidity. Additive of fillers with high reflectance in mid-wave infrared is effective, low cost and convenient to modified the cooling performance polymeric RCMs. In this paper, micron rectangular bismuth oxychloride (BiOCl) powders were proposed and synthesized by hydrothermal method. And, rectangular BiOCl boasts excellent mid-wave infrared reflective capacity (85%). Then, rectangular BiOCl was added into the top-layer of flexible hierarchically porous complex membrane, and improved the reflectance of porous membrane within 2.5–8 µm from 48.3% to 58.1%. While the emittance of the obtained bilayer membrane within atmospheric window was hardly affected. The membrane with BiOCl exhibited better cooling performance in humid ambient (70%), demonstrating the importance of spectral selectivity experimentally. This work proposed an effective strategy to modify spectral selectivity of RCMs and it could expand the application of radiative cooling materials in hot and humid areas.

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