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

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.