Comprehensive evaluation and analysis of a porous polymer coating for highly efficient passive radiative cooling

The ever-increasing global energy consumption has brought intense concerns about the deficiency of non-renewable energy resources. In the meantime, cooling inevitably plays an indispensable role in daily life by consuming energy. Therefore, passive radiative cooling has gradually attracted more attention due to its vast potential to reduce energy consumption. Herein, a porous polymer radiative coating (PPRC) with poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) is fabricated and the cooling performance is evaluated. The spectral reflectivity of a 360-μm thick PPRC within the wavelength band of 0.38–0.78 μm (visible wavelength band) and the wavelength band of 0.25–2.5 μm (ultraviolet, visible, and near-infrared wavelength band) is measured to be about 93% and 87%, while the emissivity within the wavelength band of 8–13 μm (atmospheric window) is measured to be about 94%, indicating that the fabricated PPRC can produce a remarkable radiative cooling capability. The efficient optical properties of the PPRC originate from the high reflective capability of the nano/micro-porous structures and the high emissive capability of the intrinsic material feature. The PPRC cooler can continuously show outstanding cooling performance outdoors due to its angular-independent reflectivity, long-term stability, and high static water contact angle. The outdoor cooling performance test results show that the temperature drop and cooling power of the PPRC cooler can reach 7.6 °C and 85.9 W/m2 at noon. At the same time, they can further be increased by 25% and 15% by adopting a nano-porous polyethene (PE) shield under the same conditions relying on the auxiliary reflection by nano-porous PE film. In a word, the environmental-friendly PPRC cooler is likely to have a growing influence in the foreseeable future for energy saving and emission reduction.