Bioinspired Hierarchical Radiative‐Phase Change Hybrid Cooling Composite with Record‐Breaking Cooling Power

Passive daytime radiative cooling (PDRC) offers a sustainable route to reducing cooling energy consumption and greenhouse gas emissions. However, conventional PDRC materials exhibit limited cooling power (<150 W m^-2), insufficient for growing cooling demands. While integrating phase change materials enhances cooling capacity, to balance radiative cooling, latent heat, and heat transfer performances remains challenging due to their conflicting requirements. Inspired by the light scattering mechanism of nacre-pearl systems, hierarchically microstructured radiative-phase change hybrid cooling (RPHC) composites with a homogeneous morphology are developed via a water pre-removal strategy. The composite combines a multilayered microfibrillated cellulose (MFC) matrix with core-shell phase change capsules (PCCs), achieving solar reflectivity of 0.969 and mid-infrared emissivity of 0.958. Efficient PCC integration provides a high latent heat of 132.1 J g^-1. This nacre-pearl-inspired design enables a record-high PRHC power of 226 W m^-2 and an average temperature reduction of 10.1 °C below ambient. Applied to building envelopes, the MFC/PCC composite reduces cooling energy use by up to 4.4%, potentially cutting global CO₂ emissions by 1.22 billion metric tons annually. Overall, this work provides innovative energy-saving materials for energy savings and carbon neutrality.