Adhesive Hydrogel Paint for Passive Heat Dissipation via Radiative Coupled Evaporation Cooling

Passive cooling technologies have shown great interest recently due to their free electricity, especially for radiative cooling (RC), and evaporation cooling (EC). While single-mode passive cooling is often limited by environmental conditions, such as sunlight, clouds, and humidity, resulting in a limited cooling performance. To address these issues, an adhesive hydrogel paint is designed for passive heat dissipation in the daytime or high workload via radiative coupled evaporation cooling (REC), which also can realize water self-replenishment at night or low workload by RC-assisted adsorption for moisture capture. Solar reflectance ${\overline{R}}_{\mathrm{solar}}$ = 0.91 and thermal emittance ${\overline{\epsilon }}_{\mathrm{LWIR}}$ = 0.94 are obtained for RC. Excellent passive heat dissipation performance can be achieved by painting it on the 3D W-shaped substrate. Compared with the flat RC paint, the REC paint on a W-shape substrate achieves a temperature drop of 5.4 °C at the heating density of 100 W m⁻², which is further increased to 11.4 °C at 400 W m⁻² due to multi-passive cooling strategies. This structural and material design provides a potential adhesive hydrogel paint for outdoor passive heat dissipation.