Adaptive Phase Change Microcapsules for Efficient Sustainable Cooling

Passive radiative cooling has recently gained significant attention as a highly promising technology that offers a zero-energy and electricity-free solution to tackle the pressing issue of global warming. Nevertheless, research efforts have predominantly focused on enhancing daytime and hot-day radiative cooling efficacy, often neglecting the potential downsides associated with excessive cooling and the consequent increased heating expenses during cold nights and winter days. Herein, we demonstrate a micro-nanostructured engineered composite film that synergistically integrates room-temperature adaptive silica-shell/oil-core phase change microcapsules (S-PCMs) with commercially available cellulose fibers. The resultant composite film exhibits a solar reflectance of 0.92 and a mid-infrared emissivity of 0.96, achieving a remarkable average daytime subambient cooling of 7.5 °C under direct sunlight in hot conditions. Encouragingly, upon reaching the phase transition temperature, the heat previously absorbed and stored by S-PCMs is released, resulting in a temperature elevation of the composite film with an average temperature differential of merely 3.0 °C compared to surrounding air. The exceptional latent heat storage capability of our S-PCMs/cellulose composite film mitigates the radiative overcooling effect and substantially diminishes the heating demand, particularly across a diverse array of environmental conditions.