Hierarchically Patterned Self-Cleaning Polymer Composites for Daytime Radiative Cooling

Designing the Future of Cooling: Superhydrophobic Passive Daytime Radiative Cooling Systems

Passive daytime radiative cooling (PDRC) is a sustainable technology that reduces temperature by utilizing materials with high solar reflectance and thermal emittance to provide cooling without electricity. However, its performance is often compromised by dust and environmental contamination, with even minimal dust deposition (0.1 mg/cm2) reducing cooling capacity by ∼7.1 W/m2. To overcome this, superhydrophobicity has been integrated into PDRC systems through various techniques and materials. This Review explores superhydrophobic PDRC (SH-PDRC) systems, examining their principles, preparation strategies, and material innovations. Advanced fabrication methods, including electrohydrodynamics, phase separation, chemical vapor deposition, and layered patterns, have enabled the development of hierarchical structures that optimize solar reflectance, infrared emissivity, and water repellency. A variety of polymeric, inorganic, and hybrid materials is used to achieve durability, thermal stability, and environmental resilience. These materials are tailored to enhance performance for long-term use in extreme conditions, ensuring a high radiative cooling efficiency. SH-PDRC systems have potential applications in wearable textiles, agricultural greenhouses, and food preservation, demonstrating their versatility. By summarizing recent progress and challenges, this Review aims to provide researchers with clear guidelines for fabricating advanced SH-PDRC systems that achieve enhanced cooling performance, environmental durability, and efficiency, paving the way for designing the future of cooling.

Autonomous Noncoalescence among Water Drops through Nanopore-Induced Self-Warping

A pervasive phenomenon in nature and technology events is that the interaction among water-based volumes leads to coalescence and thus losing their individuality. Herein, we report a framework in which the opposite can be true: the interaction between adjacent water droplets on a nanoporous thin-film surface spontaneously manifests an autonomous noncoalescing action to drive the topographic emergence of macrostructural organization, based in the hydraulic control exerted by water self-confined in nanopores (avoiding the need to resort to chemical approaches for aqueous partitions). Accordingly, we also introduce strategies to perform the shaping of water through water to tailor droplet contact area shapes and local interdroplet dosing of regents. The observation of crowded water drops warping rather than coalescing reveals novel fluid manipulation with high spatial resolution and offers new possibilities of broad applicability ranging from artificial cell compartmentalization, biochemical analysis, and thermal management to hydro-smart surfaces innovation.

Materials in Radiative Cooling Technologies

Radiative cooling (RC) is a carbon-neutral cooling technology that utilizes thermal radiation to dissipate heat from the Earth's surface to the cold outer space. Research in the field of RC has garnered increasing interest from both academia and industry due to its potential to drive sustainable economic and environmental benefits to human society by reducing energy consumption and greenhouse gas emissions from conventional cooling systems. Materials innovation is the key to fully exploit the potential of RC. This review aims to elucidate the materials development with a focus on the design strategy including their intrinsic properties, structural formations, and performance improvement. The main types of RC materials, i.e., static-homogeneous, static-composite, dynamic, and multifunctional materials, are systematically overviewed. Future trends, possible challenges, and potential solutions are presented with perspectives in the concluding part, aiming to provide a roadmap for the future development of advanced RC materials.

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.

Pushing Radiative Cooling Technology to Real Applications

Radiative cooling is achieved by controlling surface optical behavior toward solar and thermal radiation, offering promising solutions for mitigating global warming, promoting energy saving, and enhancing environmental protection. Despite significant efforts to develop optical surfaces in various forms, five primary challenges remain for practical applications: enhancing optical efficiency, maintaining appearance, managing overcooling, improving durability, and enabling scalable manufacturing. However, a comprehensive review bridging these gaps is currently lacking. This work begins by introducing the optical fundamentals of radiative cooling and its potential applications. It then explores the challenges and discusses advanced solutions through structural design, material selection, and fabrication processes. It aims to provide guidance for future research and industrial development of radiative cooling technology.

Supramolecularly Connected Armor-like Nanostructure Enables Mechanically Robust Radiative Cooling Materials

Passive daytime radiative cooling (PDRC) is a promising practice to realize sustainable thermal management with no energy and resources consumption. However, there remains a challenge of simultaneously integrating desired solar reflectivity, environmental durability, and mechanical robustness for polymeric composites with nanophotonic structures. Herein, inspired by a classical armor shell of a pangolin, we adopt a generic design strategy that harnesses supramolecular bonds between the TiO2-decorated mica microplates and cellulose nanofibers to collectively produce strong interfacial interactions for fabricating interlayer nanostructured PDRC materials. Owing to the strong light scattering excited by hierarchical nanophotonic structures, the bioinspired film demonstrates a desired reflectivity (92%) and emissivity (91%) and an excellent temperature drop of 10 °C under direct sunlight. Notably, the film guarantees high strength (41.7 MPa), toughness (10.4 MJ m-3), and excellent environmental durability. This strategy provides possibilities in designing polymeric PDRC materials, further establishing a blueprint for other functional applications like soft robots, wearable devices, etc.

Investigation of recycled materials for radiative cooling under tropical climate

As a sustainable alternative to using virgin polymer, we propose the use of recycled polymer for the fabrication of passive radiative cooling materials to tackle both the increasing demand for cooling systems and to upcycle plastic waste. Using recycled acrylic sheets as the binder for BaSO4 thorough sol-gel method, a sustained 1.2 °C sub-ambient temperature during daytime and 3 °C sub-ambient temperature during nighttime was achieved under the hot and humid conditions of the tropical climate. The coating achieved 97.7 % solar reflectance and 95 % infrared emittance. Separately, when porosity is introduced to recycled acrylic sheets through a phase inversion method, a near-ambient temperature during noontime and sustained sub-ambient temperature of 2.5 °C during nighttime was achieved (with 96.7 % solar reflectance). Comparable performances are also obtained using recycled polyvinyl chloride (PVC) pipe and expanded polystyrene (EPS) foam.

Anti-Environmental Aging Passive Daytime Radiative Cooling

Passive daytime radiative cooling technology presents a sustainable solution for combating global warming and accompanying extreme weather, with great potential for diverse applications. The key characteristics of this cooling technology are the ability to reflect most sunlight and radiate heat through the atmospheric transparency window. However, the required high solar reflectance is easily affected by environmental aging, rendering the cooling ineffective. In recent years, significant advancements have been made in understanding the failure mechanisms, design strategies, and manufacturing technologies of daytime radiative cooling. Herein, a critical review on anti-environmental aging passive daytime radiative cooling with the goal of advancing their commercial applications is presented. It is first introduced the optical mechanisms and optimization principles of radiative cooling, which serve as a basis for further endowing environmental durability. Then the environmental aging conditions of passive daytime radiative cooling, mainly focusing on UV exposure, thermal aging, surface contamination and chemical corrosion are discussed. Furthermore, the developments of anti-environmental aging passive daytime radiative cooling materials, including design strategies, fabrication techniques, structures, and performances, are reviewed and classified for the first time. Last but not the least, the remaining open challenges and the insights are presented for the further promotion of the commercialization progress.