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Passive cooling permits thermal management of near-zero energy consumption and low CO2emissions. Despite significant progress of passive radiative coolers, comfortable and steady temperatures can hardly be achieved due to their inadequate daytime cooling power (below 0.2 kW m−2) yet over-cooling at night. Here, we provide a bright-white hydrogel that enables on-demand passive cooling by virtue of adaptive water evaporation and high solar reflectance up to 86.1%. Notably, theoretical cooling power determined by the evaporating rate can reach 1.25 kW m −2in daytime but decreases dramatically at night. Hence sub-ambient temperature reduction of 11–13 °C at noon yet nearly none at night are realized, with the diurnal temperature difference narrowed significantly. Moreover, effective cooling using colored hydrogels, and transition from evaporative cooling to solar heating have been demonstrated. This novel evaporative cooling approach will pave the way for smart passive coolers of high efficiency, colorful appearance, and low cost.

Optimizing the water bonding network in an evaporator is significant for efficient solar-driven vapor generation (SVG). Herein, we report a facile one-pot method to regulate the hydrated structure and wettability in a hierarchical porous hydrogel. An ovalbumin (OVA)-polyacrylamide hydrogel foam was fabricated in a cake-making fashion. Because of the enrichment of amphiphilic OVA at the interface, the hydrophobic walls of the air pores in the foam provide vaporization sites and help reduce parasitic heat loss, while the hydrophilic skeleton with the secondary pores effectively pumps capillary water. Notably, the proportion of intermediate water in the foam reaches 87.6% with the melting point as low as −10 °C. All these features contribute to an exceptional evaporation rate of 3.4–4.5 kg m–2h–1under 1 sun and robust SVG performances at high-humidity, weak sunlight, or cold weathers. The strategy of using amphiphilic molecules to optimize the hydrated structures both at the interface and in bulk promises the reasonable design of SVG materials with superior efficiency and weather adaptability.

Transparent superhydrophobic surfaces are of vital significance for rising applications in optoelectronics, outdoor displays, building windows, and so on. However, facile fabrication of surfaces combining stable superhydrophobicity and high transparency with particularly low haze remains a challenge. Here, we demonstrate a nonfluorinated hierarchical surface, simply prepared by sequential spraying of a primer of poly(ethylene-co-acrylic acid) (EAA) and silica nanoparticles (SiO2). The resultant surface shows remarkable liquid repellency (e.g., an apparent contact angle of >160° and a sliding angle of <2° for honey) and high transparency (a transmittance of ∼91% and a haze of ∼6%). Especially, flexible EAA adhesive enables the surface to resist water impinging (up to ∼15.0 m s–1, higher than the terminal velocities of raindrops) and mechanical damaging. This super-repellent surface also presents excellent UV and chemical stability, sustaining a superhydrophobic state upon UVA exposure for 60 days and acidic corrosion or oil contamination for 7 days. With multirobustness and scalability, our coatings show great potential in related fields.

Energy-saving cooling materials with strong operability are desirable for sustainable thermal management. Inspired by the cooperative thermo-optical effect in the fur of a polar bear, we develop a flexible, superhydrophobic, and reusable cooling “skin” by laminating a poly(dimethylsiloxane) film with a highly scattering polyethylene aerogel. Owing to its high porosity (97.9%) and tailored pore size of 3.8 ± 1.4 μm, it can achieve superior solar reflectance (R̅sun∼ 0.96) and high transparency to irradiated thermal energy (τ̅PE,MIR∼ 0.8) at a thickness of 2.7 mm. Combined with the low thermal conductivity (0.032 W m–1K–1) of the aerogel, the cooling skin exerts midday sub-ambient temperature drops of 5–6 °C in a metropolitan environment, with an estimated limit of 14 °C under ideal service conditions. Our generalized bilayer approach can be easily applied to different types of emitters, bridging the gap between night-time and daytime radiative cooling and paving the way for more cost-effective and scalable cooling materials.

Super black materials with extremely low reflectance and high absorption of incident light are crucial in various applications with strict optical requirements. However, the existing super black materials suffer from technical complexity in practical use whereas the underlying physics of their ultralow reflectance is still unclear. Herein, hierarchical porous carbon spheres are prepared using poly(vinylidene chloride-co-vinyl chloride) as a precursor. Dehydrochlorination treatment has proved to be very crucial for the morphology robustness of the porous polymer spheres during carbonization process. Coatings cast from the dispersion of these carbon spheres exhibit a hemispherical reflectance of <0.2% in the visible region and <0.3% in the range of 300–2000 nm, and the lowest reflectance of 0.14% can be reached. This super black coating has great advantages in its easy availability of starting materials, low equipment requirement, and high adaptability onto various substrates. Besides, a theoretical investigation suggests that a small scatterer size and low volume-filling ratio are the two most essential factors in realizing ultralow reflectance, which also offers an instructive guidance for the rational design of super black materials.