A Scalable Low-Cost Epoxy-Based Porous Coating for High-Performance Radiative Cooling Prepared via a Pickering High-Internal-Phase-Emulsion Approach

Abstract

Passive daytime radiative cooling (PDRC) technology with high solar reflectance and high infrared emissivity has been increasingly applied in green buildings. However, current PDRC designs are either high-cost or require additional multi-step fabrication processes, and both factors hinder their broader industrial application. Here, we present a low-cost, easy-to-process, scalable and uncomplicated porous epoxy-based radiative cooling coating via a simple Pickering high-internal-phase-emulsion (HIPE) approach. The obtained porous epoxy-based coating has micro- and submicropores. These hierarchical porous microstructures enable a synergistic interaction between the filler and the porous microstructure, thus enhancing the radiative cooling performance. As a result, the obtained porous epoxy-base polymer with alumina as fillers (PEP-A) coating presents a high solar reflectance of 95.6% in the wavelength range of 0.3–2.5 μm and a high infrared emissivity of 96.3% in the wavelength range of 8–14 μm, as well as a maximum subambient cooling temperature of 3.4 ℃ and an average cooling power of 105.6 W·m⁻2 under solar shortwave radiation of 123.01–134.67 W·m⁻2. Furthermore, the PEP-A coating can be easily applied via roll-coating, blade-coating, or brush-coating, and self-cures on diverse substrates like aluminum sheets, steel plates, polypropylene sheets, bricks, and wall surfaces without any additional template-extraction process. In particular, the cost of the raw materials for the PEP-A coating is 0.2–1.3% of that of previously reported radiative cooling coatings (e.g., Poly(vinylidenefluoride-co-hexafluoropropylene) and polydimethylsiloxane). The extraction-free nature, easy processability, self-curing ability, and low cost of the PEP-A coating make it very promising for large-scale PDRC production and applications.