3D-Printed Phase-Change Porous Monoliths for Adaptive Radiative Cooling with High Solar Reflectance and Latent Heat Buffering.

Passive daytime radiative cooling offers an energy-efficient pathway for zero-energy cooling of buildings, vehicles, and outdoor objects under direct sunlight. However, its practical deployment is hindered by limited cooling power and the risk of nighttime overcooling. Although incorporating phase-change materials provides latent heat buffering, achieving high solar reflectivity in such composites remains a challenge. Herein, we present a phase-change porous monolith fabricated by direct-ink-written 3D printing, enabling large-scale production, structural programmability, and adaptive radiative cooling performance. The monolith consists of a three-dimensional cellulose nanofiber porous skeleton uniformly embedded with microencapsulated phase-change materials. By combining multiple solar scattering and latent heat storage/release features, the monolith achieves a solar reflectance of 95.6%, a mid-infrared emissivity of 94.6% within the atmospheric window, and an on-demand latent heat of 124 J g-1. This phase-change radiative cooling monolith enables approximately 9.0 °C subambient cooling under direct sunlight while delaying nighttime overcooling by ∼2.5 h. This study presents an efficient strategy for developing radiative cooling materials that integrate high spectral selectivity, latent heat buffering, and scalable manufacturability.