Radiative Coupled Evaporation Cooling Hydrogel for Above-Ambient Heat Dissipation and Flame Retardancy.

By combining the merits of radiative cooling (RC) and evaporation cooling (EC), radiative coupled evaporative cooling (REC) has attracted considerable attention for sub-ambient cooling purposes. However, for outdoor devices, the interior heating power would increase the working temperature and fire risk, which would suppress their above-ambient heat dissipation capabilities and passive water cycle properties. In this work, we introduced a REC design based on an all-in-one photonic hydrogel for above-ambient heat dissipation and flame retardancy. Unlike conventional design RC film for heat dissipation with limited cooling power and fire risk, REC hydrogel can greatly improve the heat dissipation performance in the daytime with a high workload, indicating a 12.0 °C lower temperature than the RC film under the same conditions in the outdoor experiment. In the nighttime with a low workload, RC-assisted adsorption can improve atmospheric water harvesting to ensure EC in the daytime. In addition, our REC hydrogel significantly enhanced flame retardancy by absorbing heat without a corresponding temperature rise, thus mitigating fire risks. Thus, our design shows a promising solution for the thermal management of outdoor devices, delivering outstanding performance in both heat dissipation and flame retardancy.