粉煤灰-硅藻土复合相变储能材料制备及导热强化

固废资源化利用是实现节能减排的重要途径,以月桂酸为相变工作介质,以粉煤灰-硅藻土二元载体为封装材料,碳纳米管为导热剂,采用直接熔融共混法制备出月桂酸/粉煤灰-硅藻土/碳纳米管复合相变储能材料。采用热扩散渗透测试、傅里叶红外光谱仪(FTIR)、差示扫描量热仪(DSC)、热重分析仪(TGA)、无纸记录仪等分别考察了定形复合相变储能材料的承载性能、微观结构和热物性。结果表明:粉煤灰-硅藻土二元载体可有效防止月桂酸的泄漏,当二元载体中月桂酸的质量分数为28%时可制得无泄漏复合相变储能材料,且原样粉煤灰利用率为55%;FTIR结果表明复合材料中各组分之间相容性好;DSC测得其熔化相变温度为45.79℃,相变潜热为51.06 J/g;TGA分析显示月桂酸/粉煤灰-硅藻土/碳纳米管热稳定性较好;储/放热性能曲线显示加入质量分数为5%的碳纳米管时,复合相变储能材料的熔化与凝固时间分别减少60%和62.5%,传热效率得到显著改善。     

High‐Performance Thermally Conductive Phase Change Composites by Large‐Size Oriented Graphite Sheets for Scalable Thermal Energy Harvesting

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 (K_PCM) 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 K_PCM 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.     

Preparation and thermal properties of lauric acid/raw fly ash/carbon nanotubes composite as phase change material for thermal energy storage

Abstract

In this study, a novel ternary system form-stable phase change material (FSPCM) composed of lauric acid (LA)/raw fly ash (RFA)/carbon nanotubes (CNT) was prepared via low cost, easy and industrially applicable fabrication process for low-temperature heat storage. Particularly, the unmodified RFA was directly acted as supporting material to prevent the leakage of the melted LA almost at no cost. A series of leakage experiments were performed to evaluate the package efficiency. The maximum mass fraction of LA absorbed in RFA and CNT was found to be 25?wt% without the LA leakage. Hence, the LA/RFA/CNT (25/75/5?wt%) composite was characterized as FSPCM. The chemical structures, microstructure thermal properties and thermal stability of the FSPCM was investigated by Fourier transformation infrared spectroscope (FTIR), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analyzer (TGA). The SEM and FTIR results indicated that LA was adsorbed on the RFA’s surface porous or into the porous structure of CNT. And there was good chemical compatibility among LA, RFA and CNT. The DSC results demonstrated that the phase change temperatures and latent heats of LA/RFA/CNT FSPCM were 45.36?°C and 37.83?J/g for melting and 40.51?°C and 36.48?J/g for freezing, respectively. TGA analysis test revealed that the composite PCM had excellent thermal stability. Moreover, the heat transfer efficiency of LA/RFA/CNT FSPCM has been improved by the addition of RFA and CNT. In short, the LA/RFA/CNT FSPCM has a promising application prospect in low-temperature application due to feasible and in large scale industrial preparation, low-cost, simple and facile process.     

Experimental investigation on properties of composite sorbents for three-phase sorption-water working pairs

LiCl/H₂O and CaCl₂/H₂O show a great potential for sorption air-to-water and thermal energy storage (TES) with their large water sorption capacity. A concept of three-phase composite solid-liquid/gas sorption is proposed by using activated carbon fiber (ACF) felt as a porous host matrix to combine with LiCl and CaCl₂. Samples with different proportions of salts and varied mass ratios between LiCl and CaCl₂ are developed, and thermal conductivity, sorption kinetics and simultaneous thermal analysis (STA) are experimentally investigated. Results reveal that ACF is a better choice of matrix because water uptake and energy storage density of aforementioned samples are greatly increased. It appears that the composite sorbent of ALiCa30(3:1) is a promising material for sorption air-to-water and TES, with water uptake of 2.98 g g⁻¹ at 25 °C and 90% relative humidity, mass energy storage density of 0.41 kWh kg⁻¹ and volume energy storage density of 223 kWh m⁻³.     

Influence of SiO2 pore structure on phase change enthalpy of shape-stabilized polyethylene glycol/silica composites

Polyethylene glycol (PEG2000)/silica (SiO₂) composites with various weight percentages of PEG were prepared as solid–liquid shape-stabilized phase change materials using sol–gel method. In the composite, PEG and SiO₂ were chosen as the phase change substance and the supporting material, respectively. The composites were characterized by differential scanning calorimetry and scanning electron microscope. The pore structure of the SiO₂ matrix with removal of PEG was studied using N₂ adsorption analysis. The phase change enthalpy of PEG in the composite was determined. It was lower than the theoretical value, and decreased with the increase of PEG content. PEG in the composite was strongly confined during the phase transition, and the confinement effect was related with the pore structure of the silica matrix. By correlating the phase change enthalpy with the average pore diameter of the SiO₂ matrix by employing a confined phase change model with a constraint layer, the effect of the pore structure on phase transition of PEG was quantitatively evaluated. The phase change enthalpy of PEG in the composite depended on the average pore diameter of the SiO₂ matrix, the pore geometrical shape, and the thickness of the PEG constraint layer.     

聚乙二醇/壳聚糖复合物的相变行为及分子间相互作用

应用静态热机械分析(TMA)、差示扫描量热(DSC)和傅立叶转换红外光谱(FT-IR)研究了聚乙二醇(PEG)与壳聚糖(Chitosan)形成复合物的相变行为及分子间的相互作用。结果表明，当复合物中壳聚糖含量高于15％时．复合物表现出固态相转变行为；PEG与Chitosan间存在较强的分子间氢键，束缚和限制了复合物中PEG熔融态的平动自由，致使复合物在高温态下表现出固体化行为。     

聚乙二醇基复合相变材料的制备与热性能研究

利用聚乙二醇(PEG)为相变材料、以羟丙基甲基纤维素为分子骨架,采用4,4-二苯基甲烷二异氰酸酯作为交联剂,用化学接枝法成功合成了一种新型复合相变材料。采用红外光谱、差示扫描量热仪、热重仪、扫描电镜和X射线衍射仪对该复合相变材料的化学结构、相变性能、热稳定性、微观形貌和晶体结构等性能进行了表征。结果表明:该复合相变材料的相变过程表现为固-固相变的性质,其相变温度在309~323.2K范围内,相变焓值在89.8~106.8J/g之间。可见,通过化学接枝法得到的复合相变材料具有较好的相变行为,且克服了聚乙二醇在相变过程中的泄露问题。     

Multiresponsive Graphene‐Aerogel‐Directed Phase‐Change Smart Fibers

Wearable devices and systems demand multifunctional units with intelligent and integrative functions. Smart fibers with response to external stimuli, such as electrical, thermal, and photonic signals, etc., as well as offering energy storage/conversion are essential units for wearable electronics, but still remain great challenges. Herein, flexible, strong, and self‐cleaning graphene‐aerogel composite fibers, with tunable functions of thermal conversion and storage under multistimuli, are fabricated. The fibers made from porous graphene aerogel/organic phase‐change materials coated with hydrophobic fluorocarbon resin render a wide range of phase transition temperature and enthalpy (0–186 J g^?1). The strong and compliant fibers are twisted into yarn and woven into fabrics, showing a self‐clean superhydrophobic surface and excellent multiple responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion. Such aerogel‐directed smart fibers promise for broad applications in the next‐generation of wearable systems.     

A Metal‐Free,Free‐Standing,Macroporous Graphene@g‐C3N4 Composite Air Electrode for High‐Energy Lithium Oxygen Batteries

The nonaqueous lithium oxygen battery is a promising candidate as a next‐generation energy storage system because of its potentially high energy density (up to 2–3 kW kg^?1), exceeding that of any other existing energy storage system for storing sustainable and clean energy to reduce greenhouse gas emissions and the consumption of nonrenewable fossil fuels. To achieve high energy density, long cycling stability, and low cost, the air electrode structure and the electrocatalysts play important roles. Here, a metal‐free, free‐standing macroporous graphene@graphitic carbon nitride (g‐C₃N₄) composite air cathode is first reported, in which the g‐C₃N₄ nanosheets can act as efficient electrocatalysts, and the macroporous graphene nanosheets can provide space for Li₂O₂ to deposit and also promote the electron transfer. The electrochemical results on the graphene@g‐C₃N₄ composite air electrode show a 0.48 V lower charging plateau and a 0.13 V higher discharging plateau than those of pure graphene air electrode, with a discharge capacity of nearly 17300 mA h g^?1 _(composite). Excellent cycling performance, with terminal voltage higher than 2.4 V after 105 cycles at 1000 mA h g^?1 _(composite) capacity, can also be achieved. Therefore, this hybrid material is a promising candidate for use as a high energy, long‐cycle‐life, and low‐cost cathode material for lithium oxygen batteries.     

Complexation of polyethylene glycol with Sr<Superscript>2+</Superscript> and Ba<Superscript>2+</Superscript> cations in extracts containing chlorinated cobalt dicarbollide

The composition and structure of complexes that are formed in the system consisting of chlorinated cobalt dicarbollide (CCD), polyethylene glycol (PEG), and Sr²⁺ or Ba²⁺ in a polar diluent, dichloroethane or phenyl trifluoromethyl sulfone, were studied by IR and NMR spectroscopy. In extraction of Sr²⁺ and Ba²⁺ with solutions of [H₅O ₂ ⁺ PEG]CCD^–, the organic phase contains the ionic associates [M²⁺PEG]CCD ₂ ^– . The Sr²⁺ and Ba²⁺ complexes have similar composition and structure: The oxygen atoms of two OH groups and six COC groups of a PEG molecule fill the first coordination sphere of the metal ions. Also, no more than two water molecules can be coordinated in the second sphere, forming hydrogen bonds with the hydrogen atoms of two OH groups of PEG. The coordination of the OH groups of PEG with the Sr²⁺ and Ba²⁺ ions is preferable over the coordination of the COC groups, as follows from the fact that the extraction of Sr²⁺ and Ba²⁺ with CCD-PEG mixtures gets worse on replacement of the OH groups of PEG by other substituents. A considerable increase in the efficiency of Sr²⁺ and Ba²⁺ extraction with H-CCD solutions in the presence of PEG is due to the fact that all the H₂O molecules in the first coordination spheres of the M²⁺ ions are replaced by the COC and OH groups of PEG with the formation of a hydrophobic complex [M²⁺PEG](H₂O)₂.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 540–545.Original Russian Text Copyright © 2004 by Stoyanov, Smirnov, Babain, Antonov, Peterman, Herbst, Todd, Luther.     

表面活性剂协同超声分散制备还原氧化石墨烯＠月桂酸Ｇ棕榈酸复合相变材料及其表征

相变储能材料因能有效地解决能量供求中时间和空间不匹配的矛盾而备受关注。本实验首先采用熔融共混法制得月桂酸(LA)-棕榈酸(PA)低共熔混合物后,将其与还原氧化石墨烯(RGO)混合,通过超声分散制得还原氧化石墨烯@月桂酸-棕榈酸(RGO@LA-PA)复合相变材料。FT-IR、Raman、SEM、DSC和形貌稳定性的分析结果表明,RGO与LA-PA是以物理方式结合,所添加的RGO能对材料形成均匀包覆,仅1%(质量分数)的RGO就能使其导热系数提升20%为0.426 W·m-1·K-1,相变潜热为159.9 J·g-1,起始分解温度提高2 ℃;经100次热循环后,其相变潜热仅下降2%,说明RGO包覆相变材料后提高了其导热性能,改善了其渗漏现象,同时该复合相变材料还具有良好的热稳定性。     

Stabilizing Lithium–Sulfur Batteries through Control of Sulfur Aggregation and Polysulfide Dissolution

Lithium–sulfur (Li–S) batteries are investigated intensively as a promising large‐scale energy storage system owing to their high theoretical energy density. However, the application of Li–S batteries is prevented by a series of primary problems, including low electronic conductivity, volumetric fluctuation, poor loading of sulfur, and shuttle effect caused by soluble lithium polysulfides. Here, a novel composite structure of sulfur nanoparticles attached to porous‐carbon nanotube (p‐CNT) encapsulated by hollow MnO₂ nanoflakes film to form p‐CNT@Void@MnO₂/S composite structures is reported. Benefiting from p‐CNTs and sponge‐like MnO₂ nanoflake film, p‐CNT@Void@MnO₂/S provides highly efficient pathways for the fast electron/ion transfer, fixes sulfur and Li₂S aggregation efficiently, and prevents polysulfide dissolution during cycling. Besides, the additional void inside p‐CNT@Void@MnO₂/S composite structure provides sufficient free space for the expansion of encapsulated sulfur nanoparticles. The special material composition and structural design of p‐CNT@Void@MnO₂/S composite structure with a high sulfur content endow the composite high capacity, high Coulombic efficiency, and an excellent cycling stability. The capacity of p‐CNT@Void@MnO₂/S electrode is ≈599.1 mA h g^?1 for the fourth cycle and ≈526.1 mA h g^?1 after 100 cycles, corresponding to a capacity retention of ≈87.8% at a high current density of 1.0 C.     

Fast Capacitive Energy Storage and Long Cycle Life in a Deintercalation–Intercalation Cathode Material

Ni‐rich Li‐ion cathode materials promise high energy density, but are limited in power density and cycle life, resulting from their poor dynamic characteristics and quick degradation. On the other hand, capacitor electrode materials promise high power density and long cycle life but limited capacities. A joint energy storage mechanism of these two kinds is performed in the material‐compositional level in this paper. A valence coupling between carbon π‐electrons and O^2? is identified in the as‐prepared composite material, using a tracking X‐ray photoelectron spectroscopy strategy. Besides delivering capacity simultaneously from its LiNi_0.8Co_0.1Mn_0.1O₂ and capacitive carbon components with impressive amount and speed, this material shows robust cycling stability by preventing oxygen emission and phase transformation via the discovered valence coupling effect. Structural evolution of the composite shows a more flattened path compared to that of the pure LiNi_0.8Co_0.1Mn_0.1O₂, revealed by the in situ X‐ray diffraction strategy. Without obvious phase transformation and losing active contents in this composite material, long cycling can be achieved.     

Fast Supercapacitors Based on Graphene‐Bridged V2O3/VOx Core–Shell Nanostructure Electrodes with a Power Density of 1 MW kg−1

Transition metal oxides (TMOs), with their very large pseudocapacitance effect, hold promise for next generation high‐energy‐density electrochemical supercapacitors (ECs). However, the typical high resistivity of TMOs restricts the reported ECs to work at a low charge–discharge (C–D) rate of 0.1–1 V s⁻¹. Here, a novel vanadium oxides core/shell nanostructure‐based electrode to overcome the resistivity challenge of TMOs for rapid pseudocapacitive EC design is reported. Quasi‐metallic V₂O₃ nanocores are dispersed on graphene sheets for electrical connection of the whole structure, while a naturally formed amorphous VO₂ and V₂O₅ (called as VO_x here) thin shell around V₂O₃ nanocore acts as the active pseudocapacitive material. With such a graphene‐bridged V₂O₃/VO_x core–shell composite as electrode material, ECs with a C–D rate as high as 50 V s⁻¹ is demonstrated. This high rate was attributed to the largely enhanced conductivity of this unique structure and a possibly facile redox mechanism. Such an EC can provide 1000 kW kg⁻¹ power density at an energy density of 10 Wh kg⁻¹. At the critical 45° phase angle, these ECs have a measured frequency of 114 Hz. All these indicate the graphene‐bridged V₂O₃/VO_x core–shell structure is promising for fast EC development.     

Raspberry‐Shaped Thermochromic Energy Storage Nanocapsule with Tunable Sunlight Absorption Based on Color Change for Temperature Regulation

A novel raspberry‐shaped thermochromic energy storage nanocapsule (RTESN) is successfully designed and fabricated with switchable sunlight absorption capacity based on color change for temperature regulation. The RTESN is developed by grafting amino‐modified silica shell thermochromic nanoparticles (amino‐TLD@SiO₂) on the surface of epoxy‐functionalized energy storage nanocapsules (paraffin@PSG), with a total particle size about 450 nm. RTESN exhibits a deep color under low temperatures, which can absorb sunlight for heating. During the continuous thermal energy supply, paraffin@PSG is capable of storing thermal energy owing to its large latent heat capacity of 118.7 J g^–1, thereby maintaining the slow temperature increase. When the temperature is higher than the phase change temperature of paraffin@PSG, the color of amino‐TLD@SiO₂ turns to white with more reflection of sunlight so that it reduces the absorption of thermal energy and prevents the further increase of temperature. The thermal regulation behavior is confirmed by setting up a wooden house with the surface covered with RTESN. Compared with the blank wooden house, the RTESN covered wooden house (RTESN‐H) displays thermal insulation performances during heating and cooling with a maximum temperature difference of 7 °C.     

High Performance of N‐Doped Graphene with Bubble‐like Textures for Supercapacitors

Nitrogen‐doped graphene (NG) with wrinkled and bubble‐like texture is fabricated by a thermal treatment. Especially, a novel sonication‐assisted pretreatment with nitric acid is used to further oxidize graphene oxide and its binding with melamine molecules. There are many bubble‐like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets. The bubble‐like texture provides more active sites for effective ion transport and reversible capacitive behavior. The specific surface area of NG (5.03 at% N) can reach up to 438.7 m² g^?1, and the NG electrode demonstrates high specific capacitance (481 F g^?1 at 1 A g^?1, four times higher than reduced graphene oxide electrode (127.5 F g^?1)), superior cycle stability (the capacitance retention of 98.9% in 2 m KOH and 99.2% in 1 m H₂SO₄ after 8000 cycles), and excellent energy density (42.8 Wh kg^?1 at power density of 500 W kg^?1 in 2 m KOH aqueous electrolyte). The results indicate the potential use of NG as graphene‐based electrode material for energy storage devices.     

Covalent‐Organic‐Framework‐Based Li–CO2 Batteries

Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials constructed from designer molecular building blocks that are linked and extended periodically via covalent bonds. Their high stability, open channels, and ease of functionalization suggest that they can function as a useful cathode material in reversible lithium batteries. Here, a COF constructed from hydrazone/hydrazide‐containing molecular units, which shows good CO₂ sequestration properties, is reported. The COF is hybridized to Ru‐nanoparticle‐coated carbon nanotubes, and the composite is found to function as highly efficient cathode in a Li–CO₂ battery. The robust 1D channels in the COF serve as CO₂^– and lithium‐ion‐diffusion channels and improve the kinetics of electrochemical reactions. The COF‐based Li–CO₂ battery exhibits an ultrahigh capacity of 27 348 mAh g^?1 at a current density of 200 mA g^?1, and a low cut‐off overpotential of 1.24 V within a limiting capacity of 1000 mAh g^?1. The rate performance of the battery is improved considerably with the use of the COF at the cathode, where the battery shows a slow decay of discharge voltage from a current density of 0.1 to 4 A g^?1. The COF‐based battery runs for 200 cycles when discharged/charged at a high current density of 1 A g^?1.     

Microfluidic fabrication of core–sheath composite phase change microfibers with enhanced thermal conductive property

The preparation of phase change fibers with controllable morphology, structure and enhanced thermal conductive property is of particular importance to many applications and still remains a challenge. In this study, core–sheath composite phase change microfibers with enhanced thermal conductive property are successfully prepared by microfluidic strategy, which consist of Rubitherm^®27 (RT27) core and poly(vinyl butyral) (PVB) sheath blended with aluminum oxide nanoparticles (Al₂O₃ NPs). The effects of Al₂O₃ NPs on the morphologies, mechanical properties, phase change properties and thermal conductive properties of the produced composite microfibers are systematically investigated. The morphologies of the composite microfibers are continuous cylindrical shape with core–sheath structure. The modified Al₂O₃ NPs are uniformly dispersed in PVB matrix, and the thermal conductive property of the composite microfibers has improved significantly. The surface temperature of the Al₂O₃-incorporated composite microfibers changes faster than that of microfibers without Al₂O₃. The melting and crystallization times of the composite microfibers with 12% Al₂O₃ are decreased by 47.1 and 39.5%, respectively. It is expected that the results can provide a valuable guidance for fabrication of phase change microfibers with satisfactory heat conductive properties as well as fast thermal regulation properties.     

A Long‐Cycle‐Life Lithium–CO2 Battery with Carbon Neutrality

Lithium–CO₂ batteries are attractive energy‐storage systems for fulfilling the demand of future large‐scale applications such as electric vehicles due to their high specific energy density. However, a major challenge with Li–CO₂ batteries is to attain reversible formation and decomposition of the Li₂CO₃ and carbon discharge products. A fully reversible Li–CO₂ battery is developed with overall carbon neutrality using MoS₂ nanoflakes as a cathode catalyst combined with an ionic liquid/dimethyl sulfoxide electrolyte. This combination of materials produces a multicomponent composite (Li₂CO₃/C) product. The battery shows a superior long cycle life of 500 for a fixed 500 mAh g^?1 capacity per cycle, far exceeding the best cycling stability reported in Li–CO₂ batteries. The long cycle life demonstrates that chemical transformations, making and breaking covalent C? O bonds can be used in energy‐storage systems. Theoretical calculations are used to deduce a mechanism for the reversible discharge/charge processes and explain how the carbon interface with Li₂CO₃ provides the electronic conduction needed for the oxidation of Li₂CO₃ and carbon to generate the CO₂ on charge. This achievement paves the way for the use of CO₂ in advanced energy‐storage systems.     

A capric–palmitic–stearic acid ternary eutectic mixture/expanded graphite composite phase change material for thermal energy storage

This paper demonstrated a capric acid–palmitic acid–stearic acid ternary eutectic mixture/expanded graphite (CA–PA–SA/EG) composite phase change material (PCM) for low-temperature heat storage. The CA–PA–SA ternary eutectic mixture with a mass ratio of CA:PA:SA = 79.3:14.7:6.0 was prepared firstly, and its mass ratio in the CA–PA–SA/EG composite can reach as high as 90%. The melting and freezing temperatures of CA–PA–SA/EG composite were 21.33 °C and 19.01 °C, and the corresponding latent heat were 131.7 kJ kg⁻¹ and 127.2 kJ kg⁻¹. The CA–PA–SA/EG composite powders can be formed into round blocks by dry pressing easily, with much higher thermal conductivity than CA–PA–SA. Thermal performance test showed that the increasing thermal conductivity of CA–PA–SA could obviously decrease the melting/cooling time. Thermal property characterizations after 500 heating/cooling cycles test indicated that CA–PA–SA/EG composite PCM had excellent thermal reliability. Based on all these results, CA–PA–SA/EG composite PCM is a promising material for low-temperature thermal energy storage applications.