Solar Thermal Conversion Research Articles

Highly efficient solar-thermal-electric conversion based on asymmetric binary-architecture design in solid-solid composite phase change materials

The application of phase change materials (PCMs) in solar-thermal conversion is largely limited by the inherently inferior thermal conductivity (TC) and poor solar-thermal energy transition capacity of PCMs. Herein, 1,1,1-tri(hydroxymethyl)ethane@melamine foam/cellulose nanofiber/graphene nanoplate (TME@MCGx) shape-stable composite PCMs (ss-CPCMs) are prepared by encapsulating TME into MCGx aerogels. Profited by the effective heat-conducting MCG25 networks, the resulting TME@MCG25 ss-CPCM achieves high TC of 0.73 Wm-1k−1 for internal heat conduction. Meanwhile, the combination of surface photothermal etching and hydrophobic polydimethylsiloxane (PDMS) coating endows the obtained T-TME@MCG25 highly efficient solar-thermal conversation efficiency of 93.1 %, arising from the exposed 3D MCG25 skeletons for absorbing sunlight and the thin PDMS layer for preventing the absorbed solar-thermal energy from radiating and dissipating. Consequently, the solar-thermal-electric (STE) conversion system equipped with T-TME@MCG25 generates the prominent output voltage of 213.0 mV and current of 37.6 mA. Furthermore, the acquired T-TME@MCG25 exhibits remarkable hydrophobicity and self-cleaning performances, due to the micro-nano structures of MCGx skeleton surfaces and the low surface energy of PDMS coating. The design strategy of asymmetric binary-architecture containing 3D photothermal absorption layer and water repellency layer provides a valuable insight into STE energy conversion associated with hydrophobic ss-CPCMs, which can alleviate the looming energy crisis.

Phase change materials encapsulated in a novel hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage

Phase change materials (PCMs) with high energy density and stationary transition temperature are now considered promising solar energy storage mediums. However, their intrinsic poor light absorption, thermal conductivity and stability severely impede their potential applications. In this study, a novel carbonized hybrid aerogel (CHA) structure was firstly constructed by incorporating MXene and carbon nanofibers (CNFs) into a continuous phase polyamic acid salt (PAAS) aqueous solution, followed by directional freezing, vacuum drying, imidization, and carbonization processes. Finally, the composite PCMs (CPCMs) were fabricated by vacuum impregnation of PCMs into the CHAs. The CPCM, of which CHA consists of 20 wt% MXene and 10 wt% CNF@PDA, demonstrates high solar-thermal conversion efficiency (>91 %), improved thermal conductivity of 0.40 W·m−1·K−1, great thermal stability (enthalpy loss < 0.19 % after 100 cycling tests with no obvious leakage). The introduction of MXene and CNFs endows PCM with broader light absorption spectrum range. The skeleton matrix embedded with bonded MXene sheets and CNFs provides more thermal pathways, light absorption sites and carrying capacity, improves the thermal conductivity, solar-thermal conversion property and stability of PCM. In addition, CPCM also exhibits outstanding EMI SE (95 dB). The multifunctional and high-performance CPCMs shows potential to realize the effective capture and utilization of solar energy. This work provides a new strategy to construct stable and multifunctional hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage.

A cost-effective photothermal superhydrophobic coating with micro- and nano-graded structures for efficient solar energy harvesting

Solar collector coatings can solve the current energy shortage and environmental pollution by converting clean solar energy into thermal energy. However, once the coating is adhered to a liquid, the performance of the solar thermal conversion will be seriously affected. Here, a cost-effective photothermal superhydrophobic coating was designed by modulating the microstructure of a highly solar-absorbing material (MCN), followed by a simple spraying method combined with polyvinylidene fluoride resin (PVDF). The MCN in the coating provides excellent photothermal conversion performance, hence, the surface temperature of the coating can be rapidly increased to 97.5 °C at 1 kW/m2. In addition, the coating achieves a water contact angle (WCA) of 155.79° due to the combined micro-nano structure of MCN and PVDF coupled with the low surface energy of PVDF. More importantly, the coating possesses excellent mechanical properties and can be applied to different substrates. This cost-effective photothermal superhydrophobic coating has promising applications in outdoor environments such as insulated tents and waterproof insulation packaging.

Anisotropic Rotunda-Shaped Carboxymethylcellulose/Carbon Nanotube Aerogels Supported Phase Change Materials for Efficient Solar-Thermal Energy Conversion.

For the drawbacks of phase change materials such as poor shape stability and weak solar-thermal conversion ability, a rotunda-shaped carboxymethylcellulose/carbon nanotube aerogel (CA) with three-dimensional network was constructed by freeze casting with a special mold, and then impregnated with polyethylene glycol (PEG) in this work. The PEG/CA had an enthalpy of 183.21 J/g, and a thermal conductivity of 0.324 W m-1 K-1, which was 57 % higher than the pure PEG. The ability of PEG/CA to convert solar energy to thermal energy was a positive correlation between the inclusion of CNTs and the composite material's thermal conductivity. Under simulated sunlight, its solar-thermal conversion efficiency reaches 94.41 %, and after 10 min of irradiation, the surface temperature can reach 65 °C and the internal temperature can reach 44.67 °C. This rotunda-shaped PEG/CA is promising for the efficient use of renewable solar energy due to its strong solar-thermal conversion and thermal storage capabilities.

Photoelectric dual-mode triggered phase change materials for all-weather personal thermal management and shape memory

To cope with the demand of more complex and variable applications, it is urgent to develop dual-mode triggered, breathable, and shape-memory wearable heaters for all-weather personal thermal management of composite phase change materials (PCMs). Herein, after high-temperature carbonization of ZnCo-MOF (metal–organic framework) nanosheet array grown in situ on flexible and breathable carbon cloth (CC) and subsequent encapsulation of polyethylene glycol (PEG), the as-prepared PEG/CC@Co/CNT (carbon nanotube) composite PCMs exhibited good breathability, mechanical strength (tensile strength of 9.15 MPa), thermal energy storage density (114.19 J/g), and shape memory due to the synergy of flexible CC skeleton and rigid PEG. More importantly, composite PCMs possessed excellent solar-thermal (93.7 %, 100 mW/cm2) and electro-thermals (94.5 %, 2.0 V) conversion and storage capacity, benefiting from the conjugation effect of high graphitized carbon/carbon heterostructure with fast electron/photon/phonon transmission and the localized surface plasmon resonance effect of Co nanoparticles. Therefore, the integration of solar heating and Joule heating into breathable composite PCMs can be accurately used for next-generation all-weather, all-season, dual-mode triggered personal thermal management, including indoor/outdoor, daytime/night, rainy/cloudy and other complex and changeable scenarios.

Anisotropic MXene/Poly(vinyl alcohol) Composite Hydrogels with Vertically Oriented Channels and Modulated Surface Topography for Efficient Solar-Driven Water Evaporation and Purification.

Hierarchical structure and surface topography play pivotal roles in developing high-performance solar-driven evaporators for clean water production; however, there exists a notable gap in research addressing simultaneous modulation of internal microstructure and surface topography in hydrogels to enhance both solar steam generation performance and desalination efficiency. Herein, anisotropic poly(vinyl alcohol)/MXene composite hydrogels for efficient solar-driven water evaporation and wastewater purification are fabricated using a template-assisted directional freezing approach followed by precise surface wettability modulation. The resultant composite hydrogels exhibit vertically oriented channels that ensure fast water supply during evaporation, and their poly(vinyl alcohol) skeletons can reduce the vaporization enthalpy of the water in the hydrogels. The incorporation of MXene sheets enables efficient solar light absorption and solar-thermal conversion while providing structural reinforcement to the hydrogels. More importantly, the as-created undulating solar-thermal surface, featuring modulated hydrophilic troughs and hydrophobic crests, significantly enhances solar-thermal conversion efficiency, thereby boosting solar evaporation performances. As a result, the fabricated hydrogel-based evaporator exhibits an impressive evaporation rate of 2.55 kg m-2 h-1 under 1 sun irradiation, coupled with long-term durability and desalination stability. Notably, the outstanding mechanical robustness of the hydrogel further enables high portability through a readily achievable process of reversible dehydration/hydration.

Anisotropic and hierarchical porous boron nitride/graphene aerogels supported phase change materials for efficient solar-thermal energy conversion

The formation of shape-stabilized composite phase change materials (CPCMs) with special structure is an efficient strategy to prevent the leakage of phase change materials (PCMs) and improve the solar-thermal conversion ability. In this work, graphene and boron nitride nanosheets (BBNS) were prepared by the magnesiothermic reduction SHS method in CO2 and N2 atmosphere, respectively. Then, an anisotropic and hierarchical porous boron nitride/graphene aerogel with three-dimensional network was constructed by directional ice-freezing method using carboxymethyl cellulose as supporting framework and adhesive, and polyethylene glycol (PEG) was impregnated to prepare novel CPCMs. The CPCMs had enthalpies of 150∼160 J/g, and a highest thermal conductivity of 0.390 W/(m·K), which was around 47% higher than that of pure PEG. The ability of the CPCMs to convert solar energy to thermal energy was significantly enhanced. Under a simulated light intensity of sunlight (100 mW/cm2), its solar-thermal conversion efficiency reaches 94.92%, and after 20 min of irradiation, the surface temperature can reach 72 °C. These CPCMs are promising for the efficient use of renewable solar energy due to their high solar-thermal conversion efficiency and thermal storage capabilities.

Analysis of heat and mass transfer in a porous solar thermochemical reactor

Solar thermochemistry shows great potential as a viable solution for addressing the challenge of energy storage. The design of the reactor is still challenging the development and rapid upscaling of solar thermal conversion and storage processes. This study presents a novel reactor that capable of gas reheating and develops a comprehensive three-dimensional model that effectively couples the processes of heat transmission, gas flow and chemical reaction for the optimization of the reactor. It is demonstrated that the maximum thermal efficiency is 43.67% as the incident solar power is 3730 W, but it decreases as the temperature rises. The re-radiation loss at the reactor front face is found as a major factor affecting the reactor thermal efficiency. The result indicates that the thermal efficiency of the reactor is significantly improved as using the cutoff wavelength coating technology. As the cutoff wavelength is 1 μm, the average temperature of porous material increases from 1510.77 °C to 1634.87 °C at 60 min, and the reactor's thermal efficiency increases from 11.65% to 13.51%. This study provided comprehensive insights into heat and mass transfer in a porous solar thermochemical reactor.

Economical and shape-stabilized hydrated salt/bagasse biomass-derived carbon phase change composite for thermal energy storage

Due to their high heat storage density, low cost, and non-inflammability, hydrated salts have significant potential for application in thermal energy storage for buildings. Hydrated salts, however, have a few drawbacks, including high supercooling degree, unstable shape, and phase separation. In general, materials such as graphite, aerogel, and foam metal are commonly used to provide support for hydrated salts in order to mitigate or eliminate their drawbacks. While these currently used supporting materials have expensive and complicated production procedures. In this study, we developed bagasse biomass-derived carbon (BBC) materials to obtain easily accessible, cost-effective, and environmentally friendly support materials. Using the high-temperature carbonization method, the bagasse made from biological waste displayed a highly oriented and stacked lamellar structure. This not only significantly lowered the cost but also made the storage of hydrated salts easier. A straightforward vacuum impregnation technique was used to create SSD-SC/BBC phase change composites (PCCs). In comparison to sodium sulfate decahydrate (SSD), the developed SSD-SC/BBC9 PCCs exhibited a higher thermal storage capacity of 161.5 J/g, along with an exceptionally low supercooling degree. They also demonstrated the higher thermal conductivity of 1.79 W·m−1·K−1, improved thermal reliability, and enhanced solar-thermal energy conversion ability. Compared to other support materials, the economic analysis using static and dynamic payback periods demonstrates that the utilization of biomass-derived carbon as a support material for phase change materials (PCMs) is cost-effective, with lower preparation costs and a shorter payback period. A simple, affordable, and environmentally friendly method for utilizing hydrated salts in thermal energy storage for buildings is provided by SSD-SC/BBC9 PCCs.

High latent heat phase change materials composites based on MXene/biomass-derived cellulose nanocrystalline aerogel for solar-thermal energy conversion and storage

In this study, novel tetradecylamine/MXene/cellulose nanocrystal composite phase change materials (TDA/MXene/CNC CPCMs) were prepared using a vacuum impregnation method. For the first time, lightweight MXene/CNC composite aerogel was employed as a support material in energy storage, with TDA serving as the phase change material. The latent heat of TDA/MXene/CNC CPCMs reached 221.5 J/g. Furthermore, the density of the MXene/CNC-2 composite aerogel was 0.0614 g/cm3, and its loading rate for TDA was as high as 90.6 wt%. Additionally, the thermal conductivity of TDA/MXene/CNC CPCM-5 was 0.491 W/(m·K), 1.87 times higher than that of pure TDA. The TDA/MXene/CNC CPCMs exhibited exceptional thermal stability up to 120 °C and maintained excellent shape stability at 60 °C. The composites exhibit a superior solar-thermal conversion ability with the conversion efficiency as high as 94.1%, The incorporation of MXene significantly enhances the photothermal conversion capability, providing an important avenue for the high-efficiency utilisation of solar energy.

Waste to functions: Construction of a novel solar-thermal conversion material based on sludge-derived carbon dots via Ca-in-situ-functionalization for efficient solar-driven water evaporation

Solar interface water evaporator (SIWE) based on waste-derived carbon dots (CDs) are highly promising for large-scale production applications in the future, due to their low-cost, eco-friendly, and tunable structure and properties. However, there are still obstacles, including limited performance, blind selection of waste materials, and unknown underlying mechanisms between waste properties and the physicochemical properties of derived CDs. In this study, a novel CDs-based wooden SIWE derived from paper mill sludge (PMS) was constructed (called ESCDs-wood). Under 1 sun, ESCDs rapidly heated up from 15.6 °C to 53.5 °C and reached stability within 10 mins. The solar-thermal conversion efficiency of ESCDs was as high as 137.58 %, and the ESCDs-wood achieved a high evaporation rate of 2.94 kg m-2h−1. Moreover, the ESCDs-wood cost about $9 to complete 1 m2 evaporation. Meanwhile, the ESCDs-wood exhibited long-term stability, after 20 cycles, its solar-thermal conversion efficiency and water evaporation rate remained at 84.21 % and 85.03 % of the initial test, respectively. Moreover, the Ca-doping was found to be a key factor in effectively enhancing the solar-thermal conversion and the thermal stability of ESCDs, and the exact role of Ca-doping on the solar-thermal conversion performance enhancement of CDs was validated and revealed. Therefore, this study not only constructed a cost-effectiveness, high performance, sustainability, chemical-free, and eco-friendly SIWE, but also innovatively proposed the functionalization mechanism of Ca-doping for CDs and thus provided a new sight for the targeted regulation and design of CDs.

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion.

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Preparation of solid-solid phase change composites and their solar-interfacial water evaporation performance

Solar powered interfacial evaporation materials are widely used in seawater desalination. But solar energy is intermittent. To solve this problem, researchers combined phase change materials (PCMs) with interfacial evaporation materials. Many PCMs are loaded into the interface evaporation matrix material through physical blending, which may cause leakage problems during long-term use, leading to secondary water pollution. We have developed a novel interfacial evaporation material that continuously and efficiently vaporizes clean water under intermittent sunlight to address these issues. The solid-solid PCMs (BC/PVA/GO-g-LA-SSPCMs) were obtained by chemical grafting of PCMs lauric acid (LA) and graphene oxide (GO), and the substrate material bacterial fibrin (BC) was modified by polyvinyl alcohol (PVA). The material achieved light absorption of 88.8% in the full spectrum range. Under 1 kW m−2 light, the evaporation rate reaches 3.4 kg m−2h−1, and the solar-thermal conversion efficiency is 94.2%. In the dark, the evaporation rate is 1.05 kg m−2h−1, and the solar-thermal conversion efficiency is 49.5%. 15 light-dark cycle experiments and harsh environments (high concentration brine, acidic solution, alkaline solution, dye wastewater) showed high efficiency and stable evaporation performance. The material cost of the evaporator is about 0.98 USD·m−2, and the solar-thermal quality factor is 4.64, which is higher than that of most reported materials. In short, BC/PVA/GO-g-LA-SSPCMs provides a new idea for the future design and development of solar-thermal conversion materials to achieve efficient and continuous saltwater desalination and wastewater purification under intermittent solar-irradiation.

An ultra-high-temperature cavity receiver with a simple flat absorber for safe and efficient solar-thermal conversion

Improving the operating temperature to >1573 K is promising to enhance the generating efficiency of solar thermal power. However, such extremely ultra-high temperature inevitably brings severe challenges to solar-thermal conversion. Therefore, a cavity receiver with a simple flat absorber was designed and optimized in this study. Firstly, the receiver cavity was designed to be made of machinable insulation material, and its crucial absorbing surface was a flat absorber assembled from individual tungsten panels to simplify the structure. Then, an optical-thermal-mechanical model was established to identify the suggested configuration. It was found the partially coated receiver with a 130-mm-depth cavity and a down-in flow pattern can operate safely and efficiently under ultra-high temperatures, which was regarded as the optimized design. Finally, the performance of the optimized receiver was evaluated when the mass flow rate was within 22.0–32.0 g·s−1 and the inlet temperature was within 623∼873 K. The results indicated the highest outlet temperature reached 1579.2 K with receiver efficiency ranging from 69.9%–80.8%. Additionally, the maximum thermal losses from the glass and the insulation reached 860.2 W and 365.9 W, respectively, pointing out the crucial adiabatic directions for ultra-high-temperature receivers. The obtained results can offer promising insights to ultra-high-temperature solar receivers.

MXene-Integrated Solid-Solid Phase Change Composites for Accelerating Solar-Thermal Energy Storage and Electric Conversion.

The high thermal storage density of phase change materials (PCMs) has attracted considerable attention in solar energy applications. However, the practicality of PCMs is often limited by the problems of leakage, poor solar-thermal conversion capability, and low thermal conductivity, resulting in low-efficiency solar energy storage. In this work, a new system of MXene-integrated solid-solid PCMs is presented as a promising solution for a solar-thermal energy storage and electric conversion system with high efficiency and energy density. The composite system's performance is enhanced by the intrinsic photo-thermal behavior of MXene and the heterogeneous phase transformation properties of PCM molecular chains. The optimal composites system has an impressive solar thermal energy storage efficiency of up to 94.5%, with an improved energy storage capacity of 149.5Jg-1 , even at a low MXene doping level of 5wt.%. Additionally, the composite structure shows improved thermal conductivity and high thermal cycling stability. Furthermore, a proof-of-concept solar-thermal-electric conversion device is designed based on the optimized M-SSPCMs and commercial thermoelectric generators, which exhibit excellent energy conversion efficiency. The results of this study highlight the potential of the developed PCM composites in high-efficiency solar energy utilization for advanced photo-thermal systems.

Black kitchen waste based solar evaporator employing radiative cooling film as difffuse substrate for efficient desalination

Many substances looks black often means that these substance can completely absorb ultraviolet radiation and Visible incident light (UV). Ultraviolet and visible light account for 57 % of the incident energy of the sun. There are many substances that looks black, but have not been paid attention in the field of photothermal interface evaporation. Based on the above discussion, this paper selects the waste black round plastic lunch box and a piece of black garbage bag as solar photothermal materials to make a solar desalination device, and proves that these black garbage can be recycled and reused to make an interface solar evaporator. In this paper, a 2D desalination device with photothermal interface evaporation for solar thermal conversion was successfully fabricated using only black round plastic lunch box as photothermal material and polyester cloth as water delivery channel. In addition, a black garbage plastic bag as the only solar photothermal conversion material has also been reused in the preparation of 3D evaporators. Using the radiation cooling film as the diffuse reflection substrate, the 3D device makes the incident sunlight reflected from the radiation cooling film and polyester cloth to the black garbage plastic bag many times, making the whole evaporation device. It can reabsorb solar incident light many times. After testing, the solar energy absorption rate of the 3D evaporator is as high as 96.6 %, and the steam output is as high as 8.96 kg m−2 h−1.

Green conversion of delignified sorghum straw and polyethylene glycol into form-stable phase change materials with promising solar energy capture, transition, and storage capabilities

Phase change materials (PCMs) have attracted considerable attention as a thermal energy management technology for thermal storage. However, achieving high energy-storing abilities, low leakage rates, and solar absorption abilities simultaneously in PCMs remains greatly challenging. This research proposed a green strategy for preparing sorghum straw-based PCMs. By facile delignification and solvothermal process, delignified sorghum straw (DSS) and carbon quantum dots (CQDs) derived from removal lignin are prepared. The obtained PEG@CQDs/DSS possessed considerable reusable stabilities, excellent photo-thermal conversion properties, and thermal energy management capacities due to the delicate micropores and intrinsic noncovalent interactions among components. Especially, the PEG@CQDs-7.5/DSS exhibited superior solar-thermal conversion capabilities (with conducive photo-thermal conversion efficiency ~90.84%), and kept stable after 100 cycles of heating and cooling, in which the melting enthalpy value is ~168.1 J/g (enthalpy efficiency of ~91.11%). In conclusion, the synthesized PCMs showed potential for application in energy-saving and building thermal management.

Thermally managed and fireproof composite aerogels for safer and year-round energy saving

Seasonable and spontaneous replacement approach of daytime radiative cooling to solar thermal conversion is challenging yet imperative for year-round thermal management materials. Meanwhile, the fire safety of thermal management materials is extremely important but often overlooked. Herein, we report a bio-inspired and fireproof aerogel presenting dynamically self-switchable ability of daytime radiative cooling and solar thermal conversion, composed of thermochromic microcapsules (TC), boron nitride nanosheets (BN), and bio-based materials (alginate and phytate). In hot environments, TC/BN composite aerogel shows solar reflectivity of 91.8 % and IR emissivity of 84.3 %, promoting heat radiation to outer space and achieving an average temperature drop of ∼5.62 °C. Attributed to the thermochromic mechanism, TC/BN composite aerogel can harvest visible light of 87 % in the solar spectrum to increase the material temperature by 28.3 °C, under an environment of −8.8 °C. Based on the EnergyPlus simulation, the employment of TC/BN composite aerogel contributes to decreasing the energy consumption of buildings in both hot and cold regions, including Cairo, Singapore, Alaska, Yakutsk, and so on. Besides, the peak values of heat release rate and total heat release during the combustion of TC/BN composite aerogels are significantly decreased by 70.6 % and 58.4 %, compared to those of TC composite aerogel. The produced protective char layer enhanced by BN nanosheets is capable of isolating the fire and suppressing the fire propagation, improving the fire safety of composite aerogels designed. The TC/BN composite aerogels provide a smart thermal regulation mode for radiative cooling and solar heating, overcome the problems from changing weather and environment, and significantly promote the practical application by enhanced fire safety.

Experimental investigation of Cu@C core-shell nanoparticle suspensions for highly efficient solar-thermal conversion

The choice of working medium plays a pivotal role in achieving efficient solar-thermal utilization. Nanoparticle suspensions, due to their superior optical and thermal properties, emerge as promising candidates. However, their widespread use is hindered by high costs and a limited absorption bandwidth. In this study, Cu@C core-shell nanoparticles (NPs) were prepared through an experimental process, employing a straightforward in situ polymerization method followed by high-temperature carbonization. Finite element calculations reveals that the solar absorption power of Cu@C NPs surpasses that of C NPs and Cu NPs by 57.2 % and 22.9 %, respectively. This enhancement is attributed to the synergistic coupling between the localized surface plasmon resonance (LSPR) of the Cu core and the robust intrinsic absorption of the C shell. Under 1-sun illumination intensity, experimental findings show that the solar-thermal conversion efficiency (η) of the Cu@C nanoparticle suspension, with a mass fraction of 100 ppm, attains approximately 93 %, tripling that of the water base-fluid (∼31 %). Moreover, both η and the temperature profile exhibit negligible variations under different solar intensities and after repeated heating and cooling cycles, indicating the exceptional stability of the suspensions. These results suggest that Cu@C nanoparticle suspensions present a dependable and efficient solution for solar-thermal applications.

Recyclable Solid-Solid Phase Change Materials with Superior Latent Heat via Reversible Anhydride-Alcohol Crosslinking for Efficient Thermal Storage.

Solid-solid phase change materials (SSPCMs) with crosslinked polymer structures have received sustained interest due to their remarkable shape stability, enabling their application independently without the need for encapsulation or supporting materials. However, the crosslinking structure also compromises their latent heat and poses challenges to their recyclability. Herein, a novel strategy harnessing the internal-catalyzed reversible anhydride-alcohol crosslinking reaction to fabricate SSPCMs with superior latent heat and exceptional dual recyclability is presented. Easily accessible anhydride copolymers (e.g., propylene-maleic anhydride alternating copolymers), provide abundant reactive anhydride sites within the polymer matrix; polyethylene glycol serves as both the grafted phase change component and the crosslinker. The resulting SSPCMs attain a peak latent heat value of 156.8 J g-1 which surpasses all other reported recyclable crosslinked SSPCMs. The materials also exhibit certain flexibility and a tunable tensile strength ranging from 6.6 to 11.0 MPa. Beyond that, leveraging the reversible anhydride-alcohol crosslinks, the SSPCMs demonstrate dual recyclability through bond-exchange remolding and reversible-dissociation-enabled dissolving-recrosslinking without any reactive chemicals. Furthermore, by integrating solar-thermal conversion fillers like polydopamine nanoparticles, the potential of the system in efficient conversion, storage, and release of solar energy is highlighted.