Daytime Radiative Research Articles

Recyclable Bead Chain Structure of Ta2O5/TPU Fiber Films for Energy Harvesting and Passive Daytime Radiative Cooling

Recyclable Bead Chain Structure of Ta₂O₅/TPU Fiber Films for Energy Harvesting and Passive Daytime Radiative Cooling

Powder‐Sintered Hierarchically Porous PMMA with Optimal Pore Parameters for Passive Daytime Radiative Cooling

AbstractPorous radiative cooling polymers have drawn significant attention for passive daytime cooling due to their desirable cooling performance and easy scalability. Since optimal pore parameters (i.e., pore diameter and porosity) will enhance light scattering, polymethyl methacrylate (PMMA) powders are sintered to fabricate samples with different pore parameters by the one‐step full‐dry powder sintering method. These samples have a hierarchically porous structure with pore diameters <5.0 µm. The most porous sample has 43% porosity, 0.964 reflectance in the 0.3–2.5 µm wavelength range, and 0.967 emittance in 8–13 µm wavelength range (which is the atmospheric window). The measured cooling temperature difference decreases when the porosity is low for hierarchically porous PMMA with similar pore size distribution. The high sub‐ambient cooling temperature reduction provided by hierarchically porous PMMA with optimal pore parameters is due to high solar reflectance when illuminated by the sun. Similar cooling trends are evident when sunlight is simulated by a Xenon lamp and an optical filter. The powder‐sintered hierarchically porous PMMA with optimal pore parameters can be an excellent radiative cooler for passive daytime cooling applications.

Structurally Colored Photonic Crystal Biomimetic Microstructures for Daytime Radiative Cooling.

Daytime radiative cooling offers a novel solution to the energy crisis, enabling green and efficient thermal management in space. High reflectance in the solar spectrum is essential for passive radiative cooling, rendering dye coloring and similar methods unsuitable for colored coolers. This paper presents a structurally colored photonic crystal biomimetic microstructured radiative cooler. Inspired by natural biological systems, this cooler features a dual-layered microtruncated-cone array structure on the surface and bottom membrane layers. The silver reflector and 3D micrograting surface structure produce continuous iridescent colors through multiple interference effects. Optimized lithographic process enable the fabrication of the ordered dual-layer surface microstructure arrays with precise angular combinations. The dual-layered microtruncated-cone introduces a gradient refractive index, reducing impedance mismatch at the interface. As a result, the radiative cooler achieves high solar spectral reflectance (0.95) and high mid-infrared emissivity (0.95). Notably, the net theoretical cooling power and the subambient temperature drop are 106.9 W m-2 and 7.4 °C, respectively, at an ambient temperature of 40 °C, with a measured average temperature reduction of 6.1 °C under direct sunlight. This performance matches that of advanced radiative coolers, striking a balance between aesthetics and radiative cooling capability.

Transparent and Thermally Stable Rare-Earth-Doped Luminescent Gallate Glass toward Passive Daytime Radiative Cooling Applications.

Currently, the implementation of passive daytime radiative cooling based on zero-energy cooling methodologies primarily focuses on polymers and composite materials, whereas the available literature on all-inorganic materials is relatively few. Here, we present a novel microcrystalline glass material CaGa0.5Al1.5O4 (CGAO), doped with rare-earth elements and prepared by the high-temperature melting method. This material exhibits long-term stability at 200 °C, coupled with an effective infrared radiation cooling function, demonstrating a 4.9 °C temperature reduction at solar noon. The energy transfer and luminescence mechanisms of Tb3+ and Sm3+ doped CGAO glass have been thoroughly investigated, along with thorough assessments of its thermal stability and hardness. The glass exhibits ultrahigh light transmission in the ultraviolet to near-infrared range, with the transmittance reaching 98% in specific spectral bands. Furthermore, it demonstrates superior luminescent thermal stability, retaining 85.6% and 71.2% of its initial luminescence intensity at 423 and 523 K, respectively. The high-temperature resistance and stability and long-term cooling properties render CGAO glass as an optimal candidate for integration into future energy-efficient and sustainable building designs.

Alumina Fiber Membrane Prepared by Electrospinning Technology for Passive Daytime Radiative Cooling

Alumina Fiber Membrane Prepared by Electrospinning Technology for Passive Daytime Radiative Cooling

A Mussel-Inspired and Recyclable Coating with Integrated Daytime Radiative Cooling and Triboelectric Energy Harvesting for Intelligent and Sustainable Buildings.

Carbon neutrality necessitates new technologies for renewable energy utilization, active regulation of heat exchange, and material recycling to promote green and intelligent building development. Currently, the integration of these functions and characteristics into a single coating material presents a significant challenge. Here, we demonstrate a novel triboelectric and radiative cooling coating with mussel-inspired architectures, fabricated using cellulose nanofibers and Mica-TiO2 as a functional mortar and brick, respectively. The abundant polar groups and specific surface area of cellulose nanofibers enable a high accumulation of induced electrostatic charges, allowing the coating to act as a tribolayer to generate triboelectric outputs. The regularly layered arrangement of Mica-TiO2 endows fire resistance to the coating, which exhibits self-extinguishing properties and maintains 45% of its original electrical output even after direct exposure to flame for 20 s. Additionally, the created multilayered stacking morphology, as well as intense group vibrations of Mica-TiO2, facilitates high reflectivity (Rsolar = 0.9) and long-wave infrared emissivity (ϵLWIR = 0.94), achieving a daytime subambient temperature drop of 5.3 °C. Notably, the coating can be recycled easily while maintaining its triboelectric, radiative cooling, and fire-resistant properties. This work provides an innovative strategy for unifying triboelectric and radiative cooling functions, as well as recyclability, into a single coating material, offering new insights for future sustainable and energy-efficient buildings.

Macro-Nanoporous Film with Cauliflower-Shaped Fibers for Highly Efficient Passive Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) is a simple and effective cooling approach that does not consume any extra energy just by highly reflecting shortwave sunlight and highly radiating infrared heat through the atmospheric windows. In recent years, the application of photonic coolers and metamaterials for PDRC has been studied. However, they usually have complex processes and high precision requirements, which seriously limit large-scale fabrication. In this paper, a high-performance polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP) PDRC fiber film was prepared by a simple and efficient electrospinning method combined with phase separation, and the obtained PVDF-HFP fibers have a cauliflower-shaped macro-nanoporous structure. The cauliflower-shaped structure provides more scattering sites of the fibers, and the fiber film with the macro-nanoporous morphology has a high scattering ability in the solar region, resulting in a high solar reflectivity of 99.65%. The PVDF-HFP porous film possesses an emissivity of 90.44% in the atmospheric window, and it can reach a maximum cooling temperature of 10.2 °C during the daytime. In addition, the excellent mechanical strength provides a guarantee for its large-scale practical application. This study offers an effective improvement strategy for the spectral performance of polymer fiber films, which is meaningful for green cooling management and reduction of carbon emission.

A UV-resistant porous composite film for radiative cooling and enhanced hydrophobicity

Passive Daytime Radiative Cooling (PDRC) offers a promising strategy to reduce surface heat by reflecting solar radiation and emitting long-wave infrared radiation into space. However, the widespread application of PDRC is currently limited by challenges such as complex fabrication processes, high costs, and the materials’ susceptibility to outdoor aging. In this work, we fabricated a cost-effective, ultraviolet (UV)-resistant porous composite (UPC) film by phase separation technology. UPC films achieve high solar reflectance (0.92) and outstanding broadband longwave infrared thermal emissivity (0.975) by adjusting particle size and mass fractions of TiO2 particles embedded in Poly (methyl methacrylate) (PMMA). When applied to a drone, the films achieve a cooling effect of 12.6°C. Notably, the mid-infrared emissivity of UPC films remained stable after prolonged exposure to UV radiation (360 hours at an irradiance of 1 W/m2), with the reflectance decreasing by only 1.3 %. Software simulations were employed to evaluate the energy savings performance of UPC films in various urban environments, showing significant energy-saving benefits. Furthermore, after treatment with the modified solution, the surface contact angle of UPC films reaches 152.5°, providing excellent resistance to contamination. This work contributes to the advancement of low-cost, durable, and energy-efficient cooling solutions.

Rational Design and Fine Fabrication of Passive Daytime Radiative Cooling Textiles Integrate Antibacterial, UV-Shielding, and Self-Cleaning Characteristics.

Passive daytime radiative cooling (PDRC) textiles hold substantial potential for localized outdoor cooling of the human body without additional energy consumption, but their limited multifunctional integration severely hinders their practical application. Herein, aluminum-doped zinc oxide (AZO) nanoparticles were purposefully introduced into poly(vinylidene fluoride) (PVDF) nanofibers via a facile electrospinning process, forming a large-scale and flexible PDRC textile with the desired antibacterial, UV-shielding, and self-cleaning capabilities. These prepared PDRC textiles present a weighted sunlight reflection rate of 92.3% and a weighted emissivity of 89.5% in the mid-infrared region. Furthermore, outdoor tests with an average solar intensity of ∼715 W/m2 demonstrated that a skin simulator temperature could be cooled by ∼16.1 °C below the ambient temperature, outperforming cotton fabric by ∼6.3 °C. Owing to the outstanding photocatalytic properties of the AZO nanoparticles, these prepared PVDF textiles exhibit antibacterial properties (Escherichia coli: 99.99%), UV-shielding performance (UPF > 50+), and superior self-cleaning capabilities, providing a cost-effective and eco-friendly avenue for daytime personal thermal management.

Color Design for Daytime Radiative Cooling: Fundamentals and Approaches

The escalating global energy crisis and the worsening global warming have intensified the heat threats posed by high temperatures. Traditional cooling methods like air conditioning are not only energy-intensive but also contribute to environmental degradation. In response, there is a pressing demand for novel, eco-friendly cooling technologies, particularly amid the growing global push for carbon neutrality. As a passive cooling method that does not require any extra power input, radiative cooling offers a promising solution, utilizing thermal radiation to cool the Earth by transferring heat directly to outer space. However, current radiative cooling materials generally have a monotonous white appearance due to their high reflectivity to solar radiation, which, considering their prospects for outdoor applications, has prompted the need for color design. Recent advancements have led to the development of colored passive radiative cooling (CPRC) materials, offering passive cooling without additional energy input, colorful aesthetic appearance, and facile preparation methods. In this review, the latest progress in CPRC materials are summarized, covering fundamental principles, various color design solutions, and potential applications. Besides, the coloration strategy including chemical, structural, and luminescent approaches for CPRC are comprehensively analyzed, providing insights into the future development and deployment of CPRC materials for outdoor energy efficient systems and thermal regulation.

Stretchable and Self-Cleaning Daytime Radiative Coolers for Human Fabric and Building Applications.

Advancements in radiative cooling technology have shown significant progress in recent years. However, the limited mechanical properties of most radiative coolers greatly hinder their practical applications, particularly in the context of human cooling fabrics. In this study, we present the fabrication of facile and stretchable radiative coolers with exceptional cooling performance by utilizing the design of porous radiative coolers as guidelines for developing promising elastomer coolers. Subsequently, we employ a simple electrospinning method to fabricate these coolers, resulting in impressive solar reflectivity (∼96.1%) and infrared emissivity (over 95%). During the summer, these coolers demonstrate a maximum temperature drop of ∼9.6 °C. Additionally, the developed coolers exhibit superior hydrophobicity and mechanical properties, with a high strain capacity exceeding 700% and a stress tolerance of over 30 MPa, highlighting their potential for application in automobile textiles and cooling fabrics. Furthermore, we evaluate the radiative cooling performance of stretchable coolers using global-scale modeling, revealing their significant cooling potential across various regions worldwide.

Scalable, Controlled Bimodal Pore-Structured Polymer Coating for Efficient Passive Daytime Radiative Cooling.

Outdoor thermal irritation poses a serious threat to public health, with the frequent occurrence of increasingly intense heat waves. With the global goal of carbon peaking and carbon neutrality, there is an urgent need for a strategy that is efficient and can provide localized outdoor cooling without an intensive energy input. This paper demonstrated a rapidly formable polyurethane-based coating with controlled bimodal spherical micropores. Nano-Al2O3 particles (300 nm) embedded in the polymer were used for targeted enhancement of reflectance at 0.38-0.5 wavelengths. The enhanced film reflected 93% solar irradiance and selectively transmitted 95% thermal radiation (8-13 μm), enabling rapid cooling and the creation of a comfortable thermal microclimate to avoid overheating of 6-11 °C during daytime conditions. The ultrawide material compatibility and excellent adaptive mechanical strength of polyurethane-based coatings are expected to benefit the sustainable development of society in a wide range of fields, from health to economics.

Comprehensive investigation of daytime radiative cooling technology for sustainable grain storage: A combined approach of field measurement and CFD simulations

Ensuring the thermal-safety of grain storage while achieving an ecologically friendly, energy-efficient solution that contributes to carbon reduction strategy is the future direction for grain storage systems. The application of Radiative Cooling (RC) technology in long-term grain storage is a promising solution in this regard. This study investigates the energy storage and heat transfer properties of the Daytime Radiative Cooling (DRC) metafilm, a type of RC material, in grain storage settings from spring to summer by performing a field measurement on a grain storage of ∼500 m2 rooftop and corresponding Computational Fluid Dynamics (CFD) simulations. The results highlight that the DRC metafilm applied to the outer roof surface achieves a peak cooling rate of 38.3 % under direct sunlight, which is a 50.6 % improvement over the non-filmed condition, providing effective heat dissipation and ensuring a continuous passive cooling process in hot environments. Especially in high-temperature summer conditions, the DRC metafilm ensures that both the average grain temperature throughout the storage and the central grain pile temperature meet the standards for quasi-low-temperature grain storage with zero energy consumption. Additionally, during the peak solar radiation intensity of summer, the DRC film acts as an efficient heat dissipator, facilitating negligible surface heat flux on the exterior roof, with localized regions exhibiting positive cooling effects. Consequently, using DRC material engenders tangible economic and substantial environmental benefits for grain storage cooling.

Highly Stable Polyimide Composite Nanofiber Membranes with Spectrally Selective for Passive Daytime Radiative Cooling.

Passive radiative cooling technology without electric consumption is an emerging sustainability technology that plays a key role in advancing sustainable development. However, most radiative cooling materials are vulnerable to outdoor contamination and thermal/UV exposure, which leads to decreased performance. Herein, we report a hierarchically structured polyimide/zinc oxide (PINF/ZnO) composite membrane that integrates sunlight reflectance of 91.4% in the main thermal effect of the solar spectrum (0.78-1.1 μm), the mid-infrared emissivity of 90.0% (8-13 μm), UV shielding performance, thermal resistance, and ideal hydrophobicity. The comprehensive performance enables the composite membrane to yield a temperature drop of ∼9.3 °C, compared to the air temperature, under the peak solar irradiance of ∼800 W m-2. In addition, the temperature drop of as-obtained composite membranes after heating at 200 °C for 6 h in a nitrogen/air atmosphere can be well maintained at ∼9.0 °C, demonstrating their ideal radiative cooling effect in a high-temperature environment. Additionally, the PINF/ZnO composite membrane shows excellent chemical durability after exposure to the outdoor environment. This work provides a new strategy to integrate chemical durability and thermal resistance with radiative cooling, presenting great potential for passive radiative cooling materials toward practical applications in harsh environments.

Flexible Passive Daytime Radiative Cooling Aerogel with Outstanding Amphiphobic Monolith Properties

Flexible Passive Daytime Radiative Cooling Aerogel with Outstanding Amphiphobic Monolith Properties

Effectiveness of Daytime Radiative Sky Cooling in Constructions

In this paper, we have carefully studied the scientific literature dealing with the use of passive radiative surfaces within the construction industry. The aim of this paper is to highlight technologies and materials for daylight radiative cooling under study today—or already on the market—and to report their main characteristics, performance and, where possible, costs. Following a review of the available scientific literature, the advantages and limitations of such an option were highlighted, seeking to capture opportunities and future lines of research development. This review also provides the physical laws that evaluate the energy balance of passive radiative surfaces as well as the criteria to quantify all the terms of these equations.

Cellulose Metamaterials with Hetero‐Profiled Topology via Structure Rearrangement During Ball Milling for Daytime Radiative Cooling

AbstractPassive radiative cooling is a zero‐energy consumption approach, which can dissipate heat to outer space by emitting infrared radiation through the transparency window. Traditional cooling materials, such as photonic films, metafabrics, and polymer foams, still suffer from complex preparation processes and high costs. In this work, it is reported that natural cellulose can be converted into a “green” optical metamaterial by rational structure reconfiguration at the micro/nano level via scalable ball milling technology for efficient daytime radiative cooling. Specifically, fine‐tuning the shearing kinetics in the mechanochemistry process, cellulosic optical metamaterial (COM) with ≈98% solar reflectivity and ≈0.97 infrared emissivity has been successfully achieved, which can break through the theoretical value of photonic crystals as well as the conventional synthetic optical materials. The COMSOL simulation reveals that the excellent optical properties of the cellulose metamaterial are explained by the “confined scattering” effect caused by the rearranged heterostructure at the micro/nano level. Outdoor tests demonstrat that the COM‐based coating exhibits a daytime radiative cooling efficiency of 5.7 °C in hot Nanjing. Meanwhile, the COM can be produced into different scattering materials via spray coating, freeze casting, and solution casting technology. This study will facilitate the development of scalable and sustainable optical metamaterials for mitigating energy consumption.

Recent Advances in Fluorescence-Based Colored Passive Daytime Radiative Cooling for Heat Mitigation

Recent Advances in Fluorescence-Based Colored Passive Daytime Radiative Cooling for Heat Mitigation

Development of Microparticle Implanted PVDF-HF Polymer Coating on Building Material for Daytime Radiative Cooling.

A passive cooling method with great potential to lower space-cooling costs, counteract the urban heat island effect, and slow down worldwide warming is radiant cooling. The solutions available frequently require complex layered structures, costly products, or a reflective layer of metal to accomplish daytime radiative cooling, which restricts their applications in many avenues. Furthermore, single-layer paints have been used in attempts to accomplish passive daytime radiative cooling, but these usually require a compact coating or only exhibit limited cooling in daytime. In our study, we investigated and evaluated in daytime the surrounding cooling outcome with aid of one layer coating composed of BaSO4/TiO2 microparticles in various concentrations implanted in the PVDF-HF polymers on a concrete substrate. The 30% BaSO4/TiO2 microparticle in the PVDF-HF coating shows less solar absorbance and excessive emissivity. The value of solar reflectance is improved by employing micro-pores in the structure of PVDF polymers without noticeable effect on thermal emissivity. The 30% BaSO4/TiO2/PVDF coating is accountable for the hydrophobicity and proportionate solar reflection in the UV band, resulting in efficient solar reflectivity of about 95.0%, with emissivity of 95.1% and hydrophobicity exhibiting a 117.1° water contact angle. Also, the developed coating could cool to about 5.1 °C and 3.9 °C below the surrounding temperature beneath the average solar irradiance of 900 W/m-2. Finally, the results demonstrate that the 30% BaSO4/TiO2/PVDF-HF microparticle coating illustrates a typical figure of merit of 0.60 and is also capable of delivering outstanding dependability and harmony with the manufacturing process.

Elevating Low-Grade Heat Harvesting with Daytime Radiative Cooling and Solar Heating in Thermally Regenerative Electrochemical Cycles.

Thermal radiation control has garnered growing interest for its ability to provide localized cooling and heating without energy consumption. However, its direct application for energy harvesting remains largely underexplored. In this work, we demonstrate a novel system that leverages daytime radiative cooling and solar heating technologies to continuously power charging-free thermally regenerative electrochemical cycle (TREC) devices, turning ubiquitous low-grade ambient heat into electricity. Notably, by harnessing a substantial 35 °C temperature differential solely through passive cooling and heating effects, the integrated system exhibits a cell voltage of 50 mV and a specific capacity exceeding 20 mAh g-1 of PB. This work unlocks the potential of readily available low-grade ambient heat for sustainable electricity generation.