Construction of Uniform Thermal Network in Passive Radiative Cooling Coatings by Nanocellulose-Mediated Pickering Emulsion Template

Developing high-performance passive radiative cooling coatings (PRCC) with high thermal conductivity for fast heat dissipation from self-heating objects remains a significant challenge. In this study, a nanocellulose-mediated Pickering emulsion strategy was employed to construct a uniform hexagonal boron nitride (BN) thermal network within PRCC. Benefiting from the Pickering emulsion template stabilized by TEMPO-oxidized cellulose nanofibrils (TOCNF), BN nanosheets and other functional inorganic nanoparticles were uniformly dispersed in the PRCC matrix, forming a continuous and homogeneous thermally conductive network. This structural design endowed the PRCC with excellent thermal conductivity, high solar reflectance in the solar spectrum (0.3–2.5 μm), and strong emissivity in the “atmospheric window” (ATSW, 8–13 μm). Specifically, the thermal conductivity of the TOCNF-BN-modified PRCC reached 2.28 ± 0.15 W·m−1·K−1, which was significantly higher than that of the pristine PRCC. The coating exhibited a solar reflectivity of ~87% and an emissivity of ~93% in the ATSW. Outdoor model temperature tests indicated that the internal temperature of the PRCC-TOCNF-BN-coated metal cabinet was 9.6 °C lower than that of the bare cabinet and 6.7 °C lower than the cabinet coated with pristine PRCC. This novel approach of using Pickering emulsion templates to fabricate highly thermally conductive radiative cooling coatings provides a new strategy for the development of high-performance and multifunctional radiative cooling materials for thermal management applications.