Bilayer

Engineering

Heat transfer

Biology

Materials science

Layer (electronics)

Passive cooling

Active cooling

Chemical engineering

Porosity

Polymer

Mechanical engineering

Genetics

Thermodynamics

Physics

Nanotechnology

Membrane

Porous medium

Composite material

Evaporative cooler

Electricity

Optoelectronics

Water cooling

Electrical engineering

Nano Energy

Passive building cooling without any electricity input are highly desirable in pursuing low energy consumption and environment protection. However, widespread adoption of existing techniques is restrained by the complex system design or low cooling power. Herein, we propose an efficient passive cooling approach with a bilayer porous polymer film, which comprises a hygroscopic hydrogel and a hydrophobic top layer with hierarchical pores. The hydrogel implements evaporative cooling in the daytime and regenerates itself at night. The top layer protects and radiatively cools the hydrogel, which enhances the cooling power during day and helps the hydrogel regeneration at night. With the synergistic effect, the bilayer film attains a remarkable sub-ambient temperature drops of ~7 °C and an effective cooling power of ~150 W·m−2 under direct sunlight, showing great potential for low-cost, efficient and scalable passive building cooling.

Bilayer porous polymer for efficient passive building cooling