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It is certainly one of the most feasible ways to extract fresh water from seawater in the face of the current depletion of fresh water resources. Although solar energy as a heat source for desalination is the cleanest and most abundant way, its intermittent and seasonal also poses an obstacle to its practical application. In order to solve the above-mentioned issues, we prepared a series of phase change composites (PCCs) with excellent light-absorbing and magnetic properties by growing MIL-101(Fe) in situ on cotton fabric. All-day desalination through the synergistic action of phase change material (PCM) and magnetic particles. The evaporation rate of PCC can reach 2.76 kg m-2h-1 with an evaporation efficiency of 90.19 % under one sunlight condition. The evaporation rate of sea water under the synergistic effect of magnetic particles and PCM reached 4.53 kg m-2h-1 in the absence of sunlight. This paper provides a new approach to all-day desalination without contact heating.

RESUMEN

The severe dependence of traditional phase change materials (PCMs) on the temperature-response and lattice deficiencies in versatility cannot satisfy demand for using such materials in complex application scenarios. Here, we introduced metal ions to induce the self-assembly of MXene nanosheets and achieve their ordered arrangement by combining suction filtration and rapid freezing. Subsequently, a series of MXene/ K+/paraffin wax (PW) phase change composites (PCCs) were obtained via vacuum impregnation in molten PW. The prepared MXene-based PCCs showed versatile applications from macroscale technologies, successfully transforming solar, electric, and magnetic energy into thermal energy stored as latent heat in the PCCs. Moreover, due to the absence of binder in the MXene-based aerogel, MK3@PW exhibits a prime solar-thermal conversion efficiency (98.4%). Notably, MK3@PW can further convert the collected heat energy into electric energy through thermoelectric equipment and realize favorable solar-thermal-electric conversion (producing 206 mV of voltage with light radiation intensity of 200 mw cm-2). An excellent Joule heat performance (reaching 105 °C with an input voltage of 2.5 V) and responsive magnetic-thermal conversion behavior (a charging time of 11.8 s can achieve a thermal insulation effect of 285 s) for contactless thermotherapy were also demonstrated by the MK3@PW. Specifically, as a result of the ordered arrangement of MXene nanosheet self-assembly induced by potassium ions, MK3@PW PCC exhibits a higher electromagnetic shielding efficiency value (57.7 dB) than pure MXene aerogel/PW PCC (29.8 dB) with the same MXene mass. This work presents an opportunity for the multi-scene response and practical application of PCMs that satisfy demand of next-generation multifunctional PCCs.

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Recently, growing interest in self-powered devices has led to the invention of new energy conversion devices. Photo-thermoelectric generators (PTEGs) have rapidly developed for their ability to harvest both light and thermal energy, but these devices are overly dependent on the continuity of energy input and cannot sustain output in an emergency situation. In the current study, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene oxide (GO)/graphene nanosheets (GNPs)/polyethylene glycol (PEG) phase-change composites (PCCs) were prepared with freeze-drying and vacuum-filling processes to acquire materials suitable for imparting energy storage characteristics to PTEGs. The melting and crystallization enthalpies of the PCCs fabricated based on the PEDOT:PSS/GO/GNP aerogels can reach 211.5 and 207.6 J g-1, respectively, which increase by nearly 5% compared with pure PEG, and the growth rate of thermal conductivity of the composites is as high as 262.7% (1.12 W m-1 K-1). Meanwhile, the excellent photothermal properties and high-temperature shape stability that pure PEG does not possess can also be imparted to PCCs by the aerogels. The PTEG assembled with PCCs and thermoelectric components can achieve a continuous output of over 1500 s after 300 s of light irradiation. After integrating the output of the device during the lamp on/off period, it is found that the total output of the device during the light-off period (8.4 V and 9.6 mW) can far exceed its total output during the light-on period (2.7 V and 4.4 mW). This work provides guidance for modulating the performance of PCCs and giving PTEGs the ability to operate under emergency or extremely harsh conditions and the prepared PTEGs are highly promising for practical use.

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Phase change materials (PCMs), which can absorb and release large amounts of latent heat during phase change, have been extensively studied for heat storage and thermal management. However, technical bottlenecks regarding low thermal conductivity and leakage have hindered practical applications of PCMs. In this paper, a simple, economical, and scalable absorption polymerization technique is proposed to prepare the polymethyl methacrylate/propyl palmitate/expanded graphite (MPCM/EG) phase change composites by constructing the microencapsulated phase change materials (polymethyl methacrylate/propyl palmitate, MPCM) with core-shell structures in the three-dimensional (3D) EG networks, taking propyl palmitate as the PCM core, polymethyl methacrylate (PMMA) as the shell, and long-chain "worm-like" EG as the thermally conductive networks. This technique proved to be a more appropriate combinatorial pathway than direct absorption of MPCM via EG. The MPCM/EG composites with high thermal conductivity, high enthalpy, excellent thermal stability, low leakage, and good thermal cycle reliability were prepared. The results showed that the MPCM-80/EG-10 composite demonstrated a high thermal conductivity of 3.38 W/(m·K), a phase change enthalpy up to 152.0 J/g, an encapsulation ratio of 90.3%, outstanding thermal stability performance, and long-term thermal cycle reliability when the EG loading is 10% and propyl palmitate is 80%. This research offers an easy and efficient approach for designing and fabricating phase change composites with promising applications in diverse energy-saving fields, such as renewable energy collection, building energy conservation, and microelectronic devices thermal protection.

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Exploiting novel strategies for simultaneously harvesting ubiquitous, renewable, and easily accessible solar energy based on the photothermal effect, and efficiently storing the acquired thermal energy plays a vital role in revolutionizing the current fossil fuel-dominating energy structure. Developing black phosphorene-based phase-change composites with optimized photothermal conversion efficiencyand high latent heat is the most promising way to achieve efficient solar energy harvesting and rapid thermal energy storage. However, exfoliating high-quality black phosphorene nanosheets  remains challenging, Furthermore, an efficient strategy that can construct the aligned black phosphorene frameworks to maximize thermal conductivity enhancement is still lacking. Herein, high-quality black phosphorene nanosheets are prepared by an optimized exfoliating strategy. Meanwhile, by regulating the temperature gradient during freeze-casting, the framework consisting of shipshape aligned black phosphorene at long-range is successfully fabricated, improving the thermal conductivity of the poly(ethylene glycol) matrix up to 1.81 W m-1  K-1 at 20 vol% black phosphorene loading. The framework also endows the composite with excellent phase-change material encapsulation capacity and  high latent heat of 103.91 J g-1 . It is envisioned that the work advances the paradigm of contrasting frameworks with nanosheets toward controllable structure thermal enhancement of the composites.

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Although single-function camouflage under infrared/visible bands has made great advances, it is still difficult for camouflage materials to cope with the synergy detection spanning both visible and infrared spectra and adapt to complex and variable scenarios. Herein, a trilayer composite integrating thermal insulation, heat absorption, solar/electro-thermal conversions, and thermochromism is fabricated for visible and infrared dual camouflages by combining anisotropic MXene/reduced graphene oxide hybrid aerogel with the n-octadecane phase change material in its bottom and a thermochromic coating on its upper surface. Benefiting from the synergetic heat-transfer suppression derived from the thermal insulation of the porous aerogel layer and the heat absorption of the n-octadecane phase-change layer, the composite can serve as a cloak to hide the target signatures from the infrared images of its ambient surroundings during the day in the jungle and at night in all scenes and can assist the target in escaping visual surveillance by virtue of its green appearance. For desert scenarios, the composite can spontaneously increase its surface temperature via its solar-thermal energy conversion, merging infrared images of the targets into the high-temperature surroundings; meanwhile, it can vary the surface color from the original green to yellow, enabling the target to visually disappear from ambient sands and hills. This work provides a promising strategy for designing adaptive and adjustable integrated camouflage materials to counter multiband surveillance in complicated environments.

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Microencapsulation of paraffin with lead tungstate shell (Pn@PWO) shows the drawbacks of low wettability and poor leakage-proof property and thermal reliability, restricting the application of phase change microcapsules. Herein, a novel paraffin@lead tungstate@silicon dioxide double-shelled microcapsule (Pn@PWO@SiO2) has been successfully constructed by the emulsion-templated interfacial polycondensation and applied in the waterborne polyurethane (WPU). The results indicated that a SiO2 layer with controlled thickness was formed on the PbWO4 shell. The Pn@PWO@SiO2 microcapsules have exhibited superior leakage-proof properties and thermal reliability through double-shelled protection, and the leakage rate decreased by at least 54.11% compared to that of Pn@PWO microcapsules. The SiO2 layer with abundant polar groups ameliorated the wettability of microcapsules and the interfacial compatibility between microcapsules and the WPU matrix. The tensile strength of WPU/Pn@PWO@SiO2-2 composites reached 10.98 MPa, which was over 7 times greater than that of WPU/Pn@PWO composites. In addition, WPU/Pn@PWO@SiO2-2 composites with a latent heat capacity of over 41 J/g exhibited efficient phase change stability and γ-ray shielding properties. Also, the mass attenuation coefficients reached 1.38 cm2/g at 105.3 keV and 1.12 cm2/g at 86.5 keV, respectively. These properties will greatly promote the application of WPU/Pn@PWO@SiO2 composites into γ-ray-shielding devices with thermal regulation.

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Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation. Featured by its exceptional thermal conductivity, graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management. Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities. Compared with conventional composite fabrications by directly mixing graphene with polymers, preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances, enabling high manufacturing flexibility and controllability. In this review, we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites. Subsequently, we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications. Finally, our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.

RESUMEN

Phase change materials (PCMs) are regarded as promising candidates for realizing zero-energy thermal management of electronic devices owing to their high thermal storage capacity and stable working temperature. However, PCM-based thermal management always suffers from the long-standing challenges of low thermal conductivity and liquid leakage of PCMs. Herein, a dual-encapsulation strategy to fabricate highly conductive and liquid-free phase change composites (PCCs) for thermal management by constructing a polyurethane/graphite nanoplatelets hybrid networks is reported. The PCM of polyethylene glycol (PEG) is first infiltrated into the cross-linked network of polyurethane (PU) to synthesize hybridized semi-interpenetrated composites (PEG@PU), and then incorporated with reticulated graphite nanoplatelets (RGNPs) via pressure-induced assembly to fabricate highly conductive PCCs (PEG@PU-RGNPs). The hybrid networks enable the PCCs to show excellent mechanical strength, liquid-free phase change, and stable thermal property. Notably, the dual-encapsulated PCCs exhibit high thermal and electrical conductivities up to 27.0 W m-1 K-1 and 51.0 S cm-1 , superior to the state-of-the-art PEG-based PCCs. Furthermore, the PCC-based energy device is demonstrated for efficient battery thermal management toward versatile demands of active preheating at a cold environment and passive cooling at a hot ambient. Overall, this work provides a promising route for fabricating highly conductive and liquid-free PCCs toward thermal management.

RESUMEN

The "solid-liquid" leakage and low thermal conductivity of organic phase change materials limit their wide range of applications. In this paper, a novel carbon fiber/boron nitride (CF/BN)-based nested structure was constructed, and then, a series of poly(ethylene glycol) (PEG)-based phase change composites (PCCs) with high thermal conductivity and mechanical strength were prepared via the simple vacuum adsorption technology by employing the CF/BN nested structure as the heat conduction path and supporting material and the in situ obtained cross-linking epoxy resin as another supporting material. The thermal conductivity of the obtained PCC is as high as 0.81 W/m K, which is 7.4 times higher than that sample without the CF/BN nested structure. The support of the double skeletons confers the obtained PCCs with excellent mechanical strength. Surprisingly, there is not any deformation for PCCs under the pressure of 128.5 times its own weight during the phase change process. In addition, the phase change enthalpy of the obtained PCC is as high as 107.9 J/g. All the results indicate that the obtained PEG-based PCCs possess huge application potential in the field of industrial waste heat recovery.

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Carbon nanomaterials have extraordinary thermal properties, such as high conductivity and stability. Nanocarbon combined with phase change materials (PCMs) can yield exceptionally high thermal effusivity composites optimal for thermal energy harvesting. The progress in synthesis and processing of high effusivity materials, and their application in resonant energy harvesting from temperature variations is reviewed.

Asunto(s)

RESUMEN

Shape-stabilized phase-change composites (SSPCCs) have been widely applied for thermal energy storage and thermal management because of their excellent properties. To further improve their thermal conductivity and thermal cycling stability, we successfully designed and synthesized a series of SSPCCs with three-dimensional (3D) thermally conductive networks by exploiting the synergistic effect between one-dimensional (1D) carbon nanotubes (CNTs) and two-dimensional (2D) hexagonal boron nitride (h-BN). The interconnected thermally conductive network composed of h-BN and multiwalled carbon nanotubes (MWCNTs) enhanced the SSPCC performance. The micromorphologies of the prepared SSPCCs revealed that well-dispersed MWCNTs, hydroxylated h-BN, and polyethylene glycol (PEG) molecular chains effectively bonded into a 3D cross-linking structure of the SSPCCs. Moreover, the chemical and crystalline structural and thermal properties and thermal cycling stability of the novel SSPCCs were systematically investigated by various characterization techniques. The presence of a 3D thermally conductive network in the as-synthesized SSPCCs evidently improved the shape stability, phase-change behavior, and thermal stability. Benefiting from the 3D nanostructural uniqueness of SSPCCs, the thermal conductivity of SSPCC-2 was up to 1.15 W m-1 K-1, which represented a significant enhancement of 239.7% compared with that of pure PEG. Meanwhile, the efficient synergistic effect of h-BN and MWCNTs remarkably enhanced the heat-transfer rate of the SSPCCs. These results demonstrate that the prepared SSPCCs have potential for applications in thermal energy storage and thermal management systems. This study opens a new avenue toward the development of SSPCCs with good comprehensive properties.

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Efficient thermal energy harvesting using phase-change materials (PCMs) has great potential for cost-effective thermal management and energy storage applications. However, the low thermal conductivity of PCMs (KPCM ) is a long-standing bottleneck for high-power-density energy harvesting. Although PCM-based nanocomposites with an enhanced thermal conductivity can address this issue, achieving a higher K (>10 W m-1 K-1 ) at filler loadings below 50 wt% remains challenging. A strategy for synthesizing highly thermally conductive phase-change composites (PCCs) by compression-induced construction of large aligned graphite sheets inside PCCs is demonstrated. The millimeter-sized graphite sheet consists of lateral van-der-Waals-bonded and oriented graphite nanoplatelets at the micro/nanoscale, which together with a thin PCM layer between the sheets synergistically enhance KPCM in the range of 4.4-35.0 W m-1 K-1 at graphite loadings below 40.0 wt%. The resulting PCCs also demonstrate homogeneity, no leakage, and superior phase change behavior, which can be easily engineered into devices for efficient thermal energy harvesting by coordinating the sheet orientation with the thermal transport direction. This method offers a promising route to high-power-density and low-cost applications of PCMs in large-scale thermal energy storage, thermal management of electronics, etc.

RESUMEN

It is important to explore and develop multifunctional phase change composites with high latent-heat capacity and photothermal conversion capability. A novel ultralight and flexible carbon foam (CF)-based phase change composite was fabricated by encapsulating n-eicosane into a CF skeleton that had been precoated with titanium(III) oxide (Ti2O3) nanoparticles (NPs). Morphological structures, as well as the properties of leakage-proof, thermal energy storage, temperature regulation, and photothermal conversion, of the fabricated phase change composites were investigated. The results indicated that the flexible CF skeleton derived from melamine foam (MF) through stabilization in air followed by carbonization in nitrogen was highly porous, which ensured excellent mechanical support and large mass ratio of n-eicosane for the composites. The loading percentage of n-eicosane as high as 84% which acted as thermal storage unit guaranteed high latent-heat capacity and good temperature regulation property of the composite; the melting/crystallization temperatures and enthalpies of the corresponding composite was 36.4/33.7 °C and 200.1/200.6 kJ·kg-1, respectively. The CF skeleton modified with Ti2O3 NPs endowed the fabricated phase change composites with enhanced leakage-proof property, photothermal conversion capability, superior thermal reliability, and temperature regulation ability. Therefore, the resultant phase change composites are believed to have promising and potential applications in solar thermal-energy storage, waste-heat recovery, and infrared stealth of military targets, and so forth.