Photothermal Storage Research Articles

Photo-thermal conversion and energy storage characteristics of magnetic phase change composites

The problem of solar intermittency can be effectively addressed by solar-to-thermal energy storage using phase change materials (PCMs). Nevertheless, intricate operating scenarios and the extreme environment of PCMs restrict their uses, and the solar energy selective absorption also impedes the attainment of high photo-thermal conversion. In this study, paraffin wax (PW) was combined with styrene-ethylene-butylene-styrene (SEBS) and magnetic nanoparticles Fe3O4 to synthesize a novel kind of magnetic PCMs (PW/SEBS/Fe3O4). Experimental verification and simulation analysis were carried out. The results have showed that the PW/SEBS/Fe3O4 achieved an overall solar absorptance of 95 %, whose energy storage capacity and photo-thermal conversion were superior to those of pure PW. The PW/SEBS/Fe3O4 showed exceptional thermal and cyclic stability, completed phase transition rapidly, and reached a greater equilibrium temperature with the rise in light intensity. Although the PW/SEBS/Fe3O4 with 1.2 g Fe3O4 has better photo-thermal storage capacity, the PW/SEBS/Fe3O4 with 2.4 g Fe3O4 has more flexible application when considering the magneto-thermal effect. Furthermore, based on the thermo-physical property, the magneto-thermal effect of the magnetic PCMs was simulated using commercial software. This research offers a new concept for solar-thermal uses of building insulation and magnetic thermal switches.

Azopyridine Polymers in Organic Phase Change Materials for High Energy Density Photothermal Storage and Controlled Release.

Azo-compounds molecules and phase change materials offer potential applications for sustainable energy systems through the storage and controllable release photochemical and phase change energy. Developing novel and highly efficient Azo-based solar thermal fuels (STFs) for photothermal energy storage and synergistic cooperation with organic phase change materials present significant challenges. Herein, three types of (ortho-, meta-, and para-) azopyridine polymers hinged with flexible alkyl chain are synthesized, in which meta-azopyridine polymer exhibits striking photothermal storage capacity of 430 J/g, providing a feasibility solution for developing high energy density Azo-based STFs. Furthermore, a stable two-phase hybrid system was innovatively constructed by combining the meta-azopyridine polymer with organic phase change materials leveraging hydrogen bonds and van der Waals interactions to collectively harness phase change energy and photothermal energy. The organic phase change material not only supplies additional phase change latent heat but also serves as a solvent, offering abundant free volume for the photo-induced isomerization of the azopyridine chromophores, which successfully circumvents the low charging efficiency in the condensed state and reliance on solvent-assisted charging in traditional Azo-based STFs. This study demonstrates the energy distribution and utilization for household consumers and the photothermal-assisted insulation strategy, achieving more extensive potential implementation for STFs.

Azopyridine Polymers in Organic Phase Change Materials for High Energy Density Photothermal Storage and Controlled Release

Azo‐compounds molecules and phase change materials offer potential applications for sustainable energy systems through the storage and controllable release photochemical and phase change energy. Developing novel and highly efficient Azo‐based solar thermal fuels (STFs) for photothermal energy storage and synergistic cooperation with organic phase change materials present significant challenges. Herein, three types of (ortho‐, meta‐, and para‐) azopyridine polymers hinged with flexible alkyl chain are synthesized, in which meta‐azopyridine polymer exhibits striking photothermal storage capacity of 430 J/g, providing a feasibility solution for developing high energy density Azo‐based STFs. Furthermore, a stable two‐phase hybrid system was innovatively constructed by combining the meta‐azopyridine polymer with organic phase change materials leveraging hydrogen bonds and van der Waals interactions to collectively harness phase change energy and photothermal energy. The organic phase change material not only supplies additional phase change latent heat but also serves as a solvent, offering abundant free volume for the photo‐induced isomerization of the azopyridine chromophores, which successfully circumvents the low charging efficiency in the condensed state and reliance on solvent‐assisted charging in traditional Azo‐based STFs. This study demonstrates the energy distribution and utilization for household consumers and the photothermal‐assisted insulation strategy, achieving more extensive potential implementation for STFs.

Highly dispersed Ag quantum dots anchored on palmitic acid/ graphitic carbon nitride composite phase change materials for enhanced photo-thermal storage

Phase change materials (PCM) have attracted much attention in the field of thermal energy storage because of exceptional heat storage capacity, stable operating temperature, and recyclability. However, organic phase change materials, represented by palmitic acid (PA), are limited by inherent leakage problem, unsatisfactory thermal responsiveness and inefficient photo-thermal storage capacity, which severely hamper the development of PCMs technology. As a means of addressing these challenges, we developed one novel support material with 2D/0D structure for palmitic acid via thermal polymerization, specifically, in which highly dispersed Ag quantum dots (Ag QDs) was firmly anchored on graphitic carbon nitride (g-C3N4). PA was further infiltrated into the layered structure of nanoporous g-C3N4/Ag QDs to successfully synthesize novel shape-stabilized PA/g-C3N4/Ag QDs composite phase change materials (CPCM). On the one hand, benefiting from the tightly stacked porous structure of g-C3N4/Ag QDs, PA is effectively encapsulated to avoid leakage problem during the solid-liquid transition with a superior adsorption capacity up to 65 %. On the other hand, the combination of g-C3N4 and Ag QDs in PA/g-C3N4/Ag QDs CPCM demonstrated a synergistic effect resulting in faster heat transfer capability and more efficient solar energy capture capability compared to pure PA, which is capable of dual utilization of heat and solar energy. The newly developed PA/g-C3N4/Ag QDs CPCM features a high melting latent heat and an appropriate phase change temperature, which are 128.35 J/g and 61.92 °C, respectively. The corresponding solidification enthalpy and temperature are 121.70 J/g and 60.02 °C. The photo-thermal conversion efficiency of the material is improved to 78.6 %, facilitating a rapid capture and storage of solar energy. Furthermore, through the optimization of the preparation process, Ag QDs are densely anchored on the surface of g-C3N4, which retains the excellent properties of metallic silver while eliminates the metal agglomeration phenomenon after repeated utilization of CPCMs. PA/g-C3N4/Ag QDs CPCM is proved to be extremely recyclable and thermally stable after massive thermal cycles. This innovative and operational encapsulation modified method significantly optimizes the practicality of phase change materials. The obtained shape-stabilized PA/g-C3N4/Ag QDs CPCM is more versatile, and its unique comprehensive properties can provide high-quality materials for photo-thermal storage systems.

Advanced Anti-Icing Strategies and Technologies by Macrostructured Photothermal Storage Superhydrophobic Surfaces.

Water is the source of life and civilization, but water icing causes catastrophic damage to human life and diverse industrial processes. Currently, superhydrophobic surfaces (inspired by the lotus effect) aided anti-icing attracts intensive attention due to their energy-free property. Here, recent advances in anti-icing by design and functionalization of superhydrophobic surfaces are reviewed. The mechanisms and advantages of conventional, macrostructured, and photothermal superhydrophobic surfaces are introduced in turn. Conventional superhydrophobic surfaces, as well as macrostructured ones, easily lose the icephobic property under extreme conditions, while photothermal superhydrophobic surfaces strongly rely on solar illumination. To address the above issues, a potentially smart strategy is found by developing macrostructured photothermal storage superhydrophobic (MPSS) surfaces, which integrate the functions of macrostructured superhydrophobic materials, photothermal materials, and phase change materials (PCMs), and are expected to achieve all-day anti-icing in various fields. Finally, the latest achievements in developing MPSS surfaces, showcasing their immense potential, are highlighted. Besides, the perspectives on the future development of MPSS surfaces are provided and the problems that need to be solved in their practical applications are proposed.

A study on novel dual-functional photothermal material for high-efficient solar energy harvesting and storage

The solar-heat storage efficiency of devices based on phase change materials (PCMs) is limited due to the light absorption and internal heat transfer within the PCMs, unclear thermal conductivity-enhancement mechanism within nanocomposite PCMs, and uncontrollable photothermal-interface modulation. Therefore, a novel controllable strategy was proposed in this study to fabricate dual-functional photothermal storage three-dimensional (3D) phase change blocks (PCBs) with higher thermal conductivity (27.98 W/m·K) and spectral absorption (98.03 %) compared to those of most previously reported PCM-based devices. The as-synthesized PCBs contained millimeter-sized graphite plates with horizontal Van der Waals bonds and oriented micro/nanoscale graphite nanosheets. The structural properties of thin PCM layers between the PCB sheets have synergistically reduced the internal interfacial thermal resistance of the PCBs. Laser-controllable induction was used to fabricate integrated biomimetic-forest 3D optical absorbers on the high thermal conductivity interface of the PCBs, which significantly reduced the thermal resistance of the optical-thermal interface. The resulting 3D-PCBs, integrated with thermoelectric generators, powered portable electronic devices, expanding the applications of traditional PCM heat-storage devices. Therefore, this study will guide the future design of high-performance solar-thermal storage PCMs with a wide range of practical applications.

Analysis of the Operating Characteristics of a Photothermal Storage Coupled Power Station Based on the Life-Cycle-Extending Renovation of Retired Thermal Power Units

Analysis of the Operating Characteristics of a Photothermal Storage Coupled Power Station Based on the Life-Cycle-Extending Renovation of Retired Thermal Power Units

Excellent Absorption of LaCoxO3 Over Full Solar Spectrum and Direct Photothermal Energy Storage of Ca(OH)2–LaCoxO3

Abstract: Photothermal conversion is a vital way for solar energy applications. The strong absorption of near Infrared light is essential for excellent photothermal performance. In this study, we demonstrated that nano LaCoxO3 is able to harvest light intensely across the full solar spectrum with high photothermal temperature. A core-shell-like structure of LaCoxO3-coated Ca(OH)2 particles was fabricated and shows excellent photothermal conversion, high kinetics of dehydration and remarkable cycle stability of heat storage and release. The photothermal dehydration-conversion of Ca(OH)2 increases 8.4-fold. Results demonstrate the multifunctionality of LaCoxO3, intensifying light harvesting, high photothermal conversion, good stability, considerable strength, and porous framework favouring the performance of photothermal storage and release cycles. LaCoxO3–Ca(OH)2 composite can simultaneously harvest light and store thermal energy.

Graphene-enhanced phase change material systems: Minimizing optical and thermal losses for solar thermal applications

Photothermal utilization systems with nano-enhanced phase change materials are encouraging due to their high cost-effectiveness, tunability, and sustainability. However, the optical and thermal losses, which have failed to be quantified and suppressed in most previous work, give rise to an intractable challenge for practical applications. Herein, we comprehensively quantify the energy flow during the photothermal conversion and storage processes and propose various strategies to suppress the optical and thermal losses for boosting solar energy utilization via experiments and numerical simulations. The results indicate that a 30 % optical loss is suppressed by introducing graphene into the phase change composite (PCC), leading to a 5.5 % increase in photothermal storage (PTS) efficiency. Compared with the graphene-doped one, the PCC achieves a 5.6 % reduction in conductive thermal loss and a 2.2 % enhancement in PTS efficiency via optimizing insulation materials. Besides, the convective loss is suppressed by employing a transparent aerogel cover, resulting in a 4.3 % increase in PTS efficiency. Furthermore, the radiant thermal loss is reduced by 21.2 % with a thermal mirror due to the reflection of infrared radiation, and thus the PTS efficiency is boosted by 9.5 %. This work's findings offer new insight into optical and thermal management for efficient solar thermal utilization.

One-Step Synthesis of Multifunctional Bacterial Cellulose Film-Based Phase Change Materials with Cross-Linked Network Structure for Solar-Thermal Energy Conversion, Storage, and Utilization.

As one of the important directions of solar energy utilization, the construction of composite photothermal phase change materials (PCM) with reasonable network support and low leakage in the simple method is important to solve the transient availability of solar energy and achieve long-lasting energy output. Here, a multifunctional silylated bacterial cellulose (BC)/hydroxylated carbon nanotube (HCNT)/polyethylene glycol (PEG) (SBTP) photothermal film-based PCM with cross-linked network structure is prepared by simple one-step synthesis. The formation of the cross-linked network structure achieves the enhancement of BC support network, prominent dispersion of HCNT and the direct introduction and perfect interlocking of PEG. Therefore, the optimal SBTP film exhibits high thermal enthalpy of 145.1Jg-1, enthalpy efficiency of over 94%, robust shape stability and low leakage of <1.2%. It also displays high photothermal conversion of over 80°C, photothermal storage of 394 sg-1 and excellent stability. Thus, it can demonstrate a maximum output voltage of 423mV and high power density of 30.26Wm-2 under three solar irradiations when applied in the solar-thermal-electric energy conversion field. Meanwhile, it also can apply in the thermal management of solar cell and light-emitting diode (LED) chip, and convert the waste heat into electricity, demonstrating multi-scene application capability.

Efficient-thermal conductivity, storage and application of bionic tree-ring composite phase change materials based on freeze casting

Thermal energy storage, management, and utilization with phase change materials have received increasing attention in industrial fields such as photo-thermal-electric conversion and integrated circuit cooling. However, the inherent low thermal conductivity and melting leakage are long-term bottlenecks that prevent their widespread commercial application. Herein, a novel composite phase change material (CPCM) with high-thermal conductivity and stability based on bionic porous SiC skeleton is proposed, which is oriented by optimized freeze casting to design vertical tree-ring porous structure for fast photo-thermal conversion and storage. The results demonstrate the novel bionic SiC skeleton can regulate the porosity (50%–70%) by changing the slurry solid content, which also exhibits good anisotropic thermal conductivity. SiC/paraffin CPCM's mass and latent enthalpy of attenuated merely by 0.87% and 1.5% after 200 repeated heat storage/exhaustion cycles, confirming its excellent longevity and stability. The high-temperature SiC/NaCl-MgCl2-KCl CPCM has a thermal conductivity of 12.54 W‧m−1‧K−1, an effective thermal-storage density per production cost of 74.5 kJ‧CNY-1, and a high photo-thermal storage efficiency of 91.8%. Finally, a variable-power chip dissipation experimental system was built to verify the thermal performance of the CPCM module in the paper. It could dissipate heat rapidly and maintain a lower temperature. This work provides a promising strategy for photo-thermal utilization and thermal management of electronic devices.

Engineering 2D MXene and LDH into 3D Hollow Framework for Boosting Photothermal Energy Storage and Microwave Absorption.

2D MXene is highly preferred for photothermal energy conversion and microwave absorption. However, the aggregation issue, insufficient dielectric loss capacity, and lack of magnetic loss capacity for MXene severely hinder its practical applications. Herein, the authors propose multi-dimensional nanostructure engineering to electrostatically assemble 2D MXene and layered double hydroxides (LDH) derived from ZIF-67 polyhedron into a 3D hollow framework (LDH@MXene), and subsequently calcined to construct a Co nanoparticle-modified 3D hollow C-LDH@MXene framework to encapsulate a paraffin wax (PW) phase change material (PCM). The 3D hollow C-LDH@MXene framework not only prevents 2D MXene from aggregation but also contributes a high thermal energy storage density (131.04 Jg-1 ). Benefiting from a 3D conductive network facilitating the rapid transport of photons and phonons from the interface to the interior and the synergistic localized surface plasmon resonance (LSPR) effect of MXene and Co magnetic nanoparticles, the C-LDH@MXene-PW composite PCM yielded a high photothermal storage efficiency of 96.52%. Besides, C-LDH@MXene-PW composite PCMs also exhibited efficient microwave absorption with a minimum reflection loss of -20.87dB at 13.30GHz with a matching thickness of only 2mm. This distinctive design provides constructive references for the development of integrated composite materials for energy storage and microwave absorption.

Enhanced light-to-thermal conversion performance of self-assembly carbon nanotube/graphene-interconnected phase change materials for thermal-electric device

Solar energy conversion and storage technologies have attracted more attention to alleviate the energy crisis and ecological concern. Further improvement on the thermal conductivity and photothermal storage capacity of phase change materials (PCMs) remain a huge challenge. In this work, a new composite PCMs employing carbon-based (CRGO) aerogel as the supporting material and paraffin wax (PW) as the PCM was prepared. We achieve a three-dimensional (3D) porous interconnected structure by cross-linking carbon nanotubes (CNT) with reduced graphene oxide (rGO). This 3D structure could provide more heat transfer channels and effective contact interfaces, resulting in its enhanced thermal conductivity. The aspect ratio of CNT and the ratio of CNT and rGO is regulated to optimize the 3D thermal conductive skeleton for CRGO aerogel. As a result, the multi-layer CRGO aerogel composite PCMs exhibited high solid-liquid phase change enthalpy (146.7 J/g) and excellent phase change stability. Optimal incorporation of 30 % CNT increased the thermal conductivity to 1.27 W/(m·K), which is 452 % higher than that of the pure PW. Meanwhile, a photothermal conversion efficiency of up to 90.3 % was achieved for the composite PCMs. In addition, the output voltage of the solar-thermal-electric device based on composite PCMs (150 mV) is about 3.75 times that of the blank plate (40 mV) under solar radiation. Therefore, CRGO aerogel composite PCMs show great promise for efficient solar-thermal-electric energy conversion utilization.

The application of magnesium nitrate hexahydrate/hybrid carbon material phase change composites in solar thermal storage

AbstractBackgroundIn this study, a series of phase change composites were developed. Phase change materials (PCMs) are substances with a high heat of fusion, thereby possessing great potential for solar thermal storage. However, their disadvantages, such as low thermal conductivity, phase separation, and supercooling, limit their further applications.ObjectiveIn this study, magnesium nitrate hexahydrate (MNH) was used as the phase change material, and different proportions of photothermal materials were added to improve the thermally conductive property and solar thermal storage efficiency of MNH.MethodsThis study used magnesium nitrate hexahydrate (MNH) as the substrate. In addition, different proportions of photothermal materials (carbon nanotubes, nano‐graphite, graphene, and partially reduced graphene oxide) were added to promote the efficiency of thermal energy storage. Additionally, a fixed ratio of carboxy methyl cellulose (CMC) was added. The phase change temperature and enthalpy change of the phase change material samples were explored and analyzed by differential scanning calorimeter (DSC). In addition, the thermophysical properties, photothermal storage performance, and thermal reliability analysis of the samples were investigated.ResultsThe results showed that the PCM composites prepared with nano‐graphite have higher latent heat and longer time of phase change. However, the composites prepared with carbon nanotubes (CNTs) have lower latent heat and a shorter time of phase change. Therefore, the partially reduced graphite oxide (PRGO)‐containing composites can retain the latent heat storage capacity of nano‐graphite and decrease the time of phase change, thereby improving the photothermal storage efficiency. The results reveal that the solar thermal storage efficiency of the composite with both CNTs and PRGO could reach up to 0.716.ConclusionsMCGOT‐1 and MCGOT‐2 have high latent heat values, and the phase transition time is short. Therefore, the thermal energy storage efficiency can be as high as 0.716. In addition, compared with related literature, the photothermal storage efficiency of MCGOT‐2 increased by about 2 times. Therefore, the environmentally friendly composites developed in this study have a high potential to be used in solar energy storage and energy‐saving systems.

MXene/rGO grafted sponge with an integrated hydrophobic structure towards light-driven phase change composites

While phase change materials (PCMs) have great potential for use in solar energy storage, they suffer from a lack of shape stability and energy conversion ability. In this study, proper amination of melamine sponge (MS) was designed to construct an integrated MXene and reduced graphene oxide (rGO) structure. The MXene/rGO layer is sufficiently robust to endure the capillary pressure caused by solvent evaporation during the airdrying process. In addition, the reduction of GO using oleylamine (OA) contributes to the protection of MXene from oxidation by preventing the surface of MXene nanosheets from being exposed to oxygen and moisture. The as-designed MXene/rGO sponges have been shown to effectively enhance the thermophysical and photo absorption properties of paraffin wax (PW) in the composite PCM. The composite with the highest amount of MXene/rGO maintained 93.3% of the latent heat of pure PW. The photothermal storage efficiency can reach as high as 93.0% at an MXene content of around 1%. A thermal conductivity enhancement of 66.9% can be achieved compared to the pure MS/PW composite. Therefore, this study presents a new approach for designing of high-performance phase change composites for waste-heat recovery and solar thermal energy storage applications.

Shape-stabilized 1-hexadecanol/g-C3N4/Cu composite phase change material with high thermal conductivity for efficient photo-thermal conversion

Phase change materials (PCM) have received much attention for thermal energy storage and release in the form of latent heat. 1-hexadecanol (HD), as a representative of organic phase change materials, has the advantages of high thermal storage density, almost constant operating temperature and stable thermochemical properties, which shows outstanding potential in the field of phase change energy storage. Nevertheless, single HD as thermal storage material inevitably faces challenges in terms of liquid phase leakage, low thermal conductivity, and poor photo-thermal conversion. To further improve the practical application of HD, we demonstrate a convenient encapsulation and modification strategy of composite phase change materials (CPCMs) with low liquid leakage and high thermal conductivity. Hence, a novel shape-stabilized Cu-doped HD/ graphitic carbon nitride (g-C3N4) CPCM was developed for efficient photo-thermal storage. By the melt blending method, HD is infiltrated into tightly stacked and aligned nano-porous g-C3N4, and the carbon-based lattice inlay achieves the encapsulation of HD to solve the leakage problem during the solid–liquid phase transition. Then, metallic Cu powder is introduced to further strengthen the thermal conductivity of the materials. With this encapsulation and modification strategy, the obtained 5 wt% Cu-doped HD/g-C3N4 composites (CPCM3) exhibits superior performance in both thermal and optical energy storage. This composite has appropriate phase change temperature and extremely high heat storage density, with melting temperature and latent heat of 48.88 °C and 249.63 J/g. The corresponding solidification temperature and latent heat is 48.52 °C and 242.22 J/g, respectively. Its thermal conductivity is enhanced to 0.5307 W/m·K, which is 59.8% higher than pure HD. The photo-thermal conversion efficiency is up to 81.6% for rapid solar energy harvesting and delivery. In particular, after 100 times thermal cycling tests and thermogravimetric analysis, this special CPCM can maintain good thermal reliability and thermal stability. In conclusion, the composite phase change materials obtained by the synergistic modification strategy of nano-porous g-C3N4 and metallic Cu significantly improved the thermochemical properties of HD. This work provides a practical and efficient synthetic strategy for the preparation of CPCMs, which is expected to present a promising future in the field of solar conversion and storage.

Enhanced thermal conductive lauric acid/g-C3N4/graphene composite phase change materials for efficient photo-thermal storage

Lauric acid (LA) shows much potential as one organic phase change material (PCM) for thermal energy storage, owing to its suitable melting point, relatively high thermal/chemical stability and latent heat. However, the LA-based thermal storage method invariably suffers from the big challenges of liquid leakage tendency and low thermal conductivity of single lauric acid, limiting immensely its practicality. Herein, one encapsulation and modifying strategy to fabricate high conductive and low liquid leakage composite phase change materials (CPCMs) for photo-thermal storage was proposed by constructing novel graphene doped LA/g-C3N4 CPCM. Firstly, LA is infiltrated into a novel two-dimensional porous matrix – the graphitic phase carbon nitride (g-C3N4) to prevent liquid leakage in the solid–liquid phase change process. Then it is further incorporated with a certain amount of graphite nanoplatelets to further enhance thermal conductivity. The encapsulation and modifying strategy enable the graphene doped LA/g-C3N4 to show excellent thermal storage performance for both heat and light energy, low liquid leakage, and high thermal stability. The hybrid LA/g-C3N4 with 5 wt% graphene (CPCM3) modification has a melting temperature of 45.88 °C and enthalpy of 159.19 J/g. The corresponding solidification temperature and enthalpy are 43.36 °C and 144.40 J/g, respectively. Its thermal conductivity at 50 °C is enhanced to 0.9338 W/(m·K) (one time higher than single LA), also superior to the state-of-the-art LA-based CPCMs. After 100 thermal cycles, the composite phase change material only suffers low mass loss and latent heat loss of phase change, which proves the good thermal reliability. Furthermore, TGA and DTG data indicate that CPCM3 can maintain good thermal stability in the normal operating temperature range. In the whole, the joint effect of the porous g-C3N4 matrix and graphene modification improve the thermal storage performance of LA through the improvement of liquid immobilization and thermal conductivity. This work provides a promising strategy for fabricating high conductive and low liquid-leakage CPCM toward enhanced photo-thermal storage.

Highly Stable MXene-Based Phase Change Composites with Enhanced Thermal Conductivity and Photothermal Storage Capability

To improve the solar energy storage efficiency and thermal conductivity, we developed stable 3D-Ti3C2Tx framework-supported composites as phase change materials (FCPCMs) fabricated by the spatial confining forced network assembly (SCFNA) method. The 3D-Ti3C2Tx framework was constructed by decomposition of a compressed mixture of NH4HCO3 and Ti3C2Tx nanosheets. The controllable porous structure of the 3D-Ti3C2Tx framework and hydrogen bonds between -OH groups (or -F groups) on the surface of MXene and the long chain of PEG benefited the good impregnation of PEG into the framework with good compatibility. Therefore, the developed PCM composites exhibited satisfactory phase change enthalpy in the range of 93.36–119.11 J/g. Compared with PEG8000, the thermal conductivity of the composite with loading 40 wt % of 3D-Ti3C2Tx increased from 0.166 to 1.733 W/(m·K). The improvement of the thermal conductivity is mainly derived from the thermal conduction path provided by the stable 3D-Ti3C2Tx framework. Based on the spatial confining forced network assembly, FCPCMs presented good shape stabilization and thermal reliability in 200 melting–freezing cycles. Benefiting from the construction of the 3D-Ti3C2Tx thermal conductivity path, the fast temperature increase rate under light irradiation is the highlight of FCPCMs. It is noted that FCPCMs exhibit both good photothermal conversion and energy storage efficiency, with the photothermal conversion and storage performance η as high as 95%. Consequently, the developed PCM composites in this work exhibited tremendous application potential in the solar energy utilization field.

Dual-functional polyethylene glycol/graphene aerogel phase change composites with ultrahigh loading for thermal energy storage

Phase change composites (PCCs) based on polyethylene glycol (PEG) benefit from the encapsulation and restraint of porous supporting network, thus to achieve the results of high loading and no leakage. The graphene aerogel (GA)/PEG composite with ultra-high loading was improved by introducing hydrogen bonds into the traditional GA preparation process to reduce the severe volume shrinkage of GA. In other words, PEG works not only as a phase change matrix, but as hydrogen bond regulator to improve the volume of GA, which realized the dual-function of PEG. The resulting PEG-mediated GA (PGA) with significantly larger volume not only has super high loading as a supporting material, but gives PEG excellent photothermal storage performance as a light absorption enhancer. X-ray diffraction (XRD) results show that the introduction of PEG increases the layer spacing of GA, which is macroscopically reflected in the inhibition of volume shrinkage. The loading percentage increases from 97.56 % to 98.89 %, and the corresponding loading multiple increases sharply from 40-fold to 89-fold, which is the highest loading known based on PEG4000 as PCM. Higher loading means higher phase transition enthalpy retention. The melting enthalpies of P-GA and P-PGA are 177.92 J/g and 183.47 J/g, and the relative enthalpy efficiency is as high as 98.12 % and 99.82 %, respectively. Simultaneously, both of them have good thermal stability and cyclic stability, photothermal conversion and heat storage capacity efficiency is about 77.97 % and 85.89 %, respectively. All characterization results show that the prepared ultra-high loading PCCs further enhance the utilization of low-grade heat energy.

Phase change composites with thermal‐formability and photothermal storage property for high flux crude oil transmission

AbstractCrude oil pipeline transportation is one of widely used ways in land transportation and comprises a large share of the world's long‐distance oil transmission. Warming and heat preservation of crude oil is vital for efficient oil pipeline transportation. However, it remains a formidable challenge in coping with caused tremendous energy consumption and environmental pollution. In this work, bio‐based phase change composites with superior thermal‐formability and photothermal storage properties were fabricated and molded to photothermal oil transportation system using template‐confined thermoforming strategy. On the basis of desirable thermal energy management ability of PEG as well as the synergistic effects between heat localization and electron nonradiative transition of Fe2O3 nanoparticles, the system realized a remarkable decrease in oil viscosity and efficient transmission. Particularly, the preparation process could be facilely scaled up and indicate real application feasibility. This successful exploration offers a significant path for developing green, highly effective crude oil transportation.