两种石墨烯修饰的复合热界面材料的制备及热性能研究

采用化学氧化还原法制备的石墨烯和化学气相沉积法制备的三维网状石墨烯共同作为导热填料改性环氧树脂,研究导热填料质量分数的变化对环氧树脂热导率的影响,并进一步测定复合热界面材料的热导率在高温下的稳定性。结果表明:当石墨烯-三维网状石墨烯的质量分数为0.2(石墨烯和三维网状石墨烯的比例为1∶9)时,可使环氧树脂的热导率提高2 400%;三维网状石墨烯的三维网状结构和石墨烯的表面官能团对复合热界面材料的热性能具有显著地影响;三维网状石墨烯为声子提供了快速传输通道,而石墨烯的表面官能团能促进环氧树脂与石墨烯之间形成良好的接触,降低界面热阻,在石墨烯和三维网状石墨烯的协同作用下可提高热界面材料的热导率。此外,可以通过优化导热填料的尺寸,提高复合热界面材料热导率的稳定性。     

基于模板法制备氧化铝纤维及其石蜡复合相变材料热性能

石蜡是一种高储热密度的有机相变材料,但是热导率低和易泄漏的缺点限制其进一步发展.为提高石蜡的导热和防泄漏性能,本研究以天然纤维为模板制备了具有高导热性的纤维状氧化铝导热填料,通过真空浸渍混合法制备了氧化铝纤维/石蜡复合相变材料,并对其形貌、热导率、相变循环稳定性、防泄漏性能以及热响应性能进行测试.结果表明,随着填料含量的增加,复合相变材料的导热系数近似线性增加.1200℃高温烧结形成的α型Al2O3比1000℃低温烧结γ型Al2O3具有更高的导热性能,且α型氧化铝纤维填充量达到45％(质量分数,余同)时,导热系数达到最高值为0.69 W/(m·K),是纯石蜡的2.9倍.通过对3种不同填充量Al2O3纤维进行100次的热循环测试,复合相变材料的相变焓值基本不变,说明了其具有良好的热循环稳定性.同时对复合相变材料的防泄漏性能以及热响应性能进行测试,结果显示30％和45％填料的α型Al2O3纤维均具有较好的防泄漏以及快速热响应能力.     

石蜡基碳纳米管复合相变材料的热物性研究

以多壁碳纳米管为填料,制备了不同质量分数(1%～5%)的石蜡基纳米复合相变材料。采用差示扫描量热技术对所制备复合相变材料的相变特性进行了表征,其导热性能则通过瞬态热线法导热仪进行了测量。实验结果发现,虽然复合相变材料的相变温度几乎不变,但其相变焓则随碳纳米管的加载量的增加而近似线性下降。在质量分数为5%时,相变焓较纯石蜡下降了约15%。复合相变材料的导热系数大致随温度的升高而降低,而在30和50℃时分别由于固固和固液相变的作用,导热系数测量值出现了较大程度的突增。此外,导热系数随质量分数呈线性增长的趋势,在质量分数为5%时,最大的相对提升率接近40%,展现了良好的导热强化效果。     

石墨烯/碳纳米管/环氧树脂复合材料的导热性能的实验研究

在微电子领域中,随着元器件的体积微小化,要求导热材料具备体积小、高导热的特点。高分子导热复合材料能很好的解决器件在不同的工作环境中仍能保持正常的散热问题。以环氧树脂(EP)为基体,石墨烯粉末(GP)和多壁碳纳米管(MWCNTs)为导热填料,采用溶剂和超声分散法,制备出石墨烯/碳纳米管/环氧树脂复合材料。实验采用瞬态电热技术测量其导热系数,结果显示,石墨烯与碳纳米管协同作为导热填料时,复合材料导热性优于单独添加导热填料(GP或MWCNTs),且随着GP所占比例的增大复合材料的导热系数越大。当GP和MWCNTs比例分别为0.7%和0.3%时,复合材料导热系数为0.940 W/(m·K),相比于纯EP导热系数提高了286.83%。     

杂化壳相变微胶囊的制备与热性能研究

采用原位聚合法以石蜡为储热芯材、二氧化钛和壳聚糖的杂化壳体为壁材、石墨烯微片（GNP）作导热填料制备一种结构稳定的防泄漏相变微胶囊。采用电镜扫描（SEM）、傅里叶红外光谱（FTIR）、热重分析法（TGA）、差示扫描量热法（DSC）和导热系数测试仪研究不同芯壳比、GNP填充量对微胶囊的微观结构、表面官能团、热稳定性、相变性能和导热性能的影响。结果表明：制得微胶囊的结构致密防泄漏性能良好，微胶囊相变潜热最高达到134.78 J/g，对应包覆率为75.51%,GNP的加入使微胶囊的导热系数提高261.5%。     

氧化石墨烯/聚乙烯醇 复合材料导热性能研究

高分子材料作为一种新型导热材料,弥补了传统导热材料如金属、金属合金等抗腐蚀性弱、力学性能差等缺陷,但其导热系数的低下导致了应用范围的局限性,而将高分子材料复合后则能很好的解决这个问题。本文以聚乙烯醇为复合材料基体,氧化石墨烯为无机填充物,经反复冷冻解冻法制备出不同体积分数梯度的氧化石墨烯/聚乙烯醇复合材料。实验采用瞬态电热测试技术对其进行导热性能测试,得出该材料达到导热系数最优点时对应的填料体积分数为25%。在实验的基础上,利用软件拟合得出导热系数值曲线图并建立导热公式,加以验证与分析。     

Preparation of form-stable carbonates/magnesium oxide-flake graphite composite thermal storage material and its thermal conductivity

以混合碳酸盐为相变材料，以氧化镁为陶瓷基骨架材料，以鳞片石墨为导热增强剂，通过混合烧结法制备出中高温复合蓄热材料。基于XRD和SEM表征分析可知，添加鳞片石墨后复合材料具有较好的化学稳定性，而且由于鳞片石墨的原因复合材料形成较多的孔隙结构。通过分析添加鳞片石墨后复合材料的热物性可知，随着鳞片石墨含量的增加，复合材料的熔点基本不变，而其热导率不断提高。鳞片石墨含量为25%的混合碳酸盐/氧化镁复合材料在250℃和560℃时的热导率分别达到3.88 W/（m·K）和2.52 W/（m·K）。基于微观结构和界面层理论对复合材料的导热增强机制进行了分析与讨论。     

纳米Fe2O3/硬脂酸/十八醇纳米复合相变蓄热材料的性能研究

针对有机相变材料热导率低的问题,将高热导率的纳米Fe₂O₃添加到硬脂酸/十八醇二元有机复合蓄热相变材料中,制备纳米复合蓄热相变材料。从分散剂的种类、分散剂与纳米材料的添加量以及超声时间4个方面研究其对纳米复合相变蓄热材料的稳定性及热物性的影响。结果表明,阴离子表面活性剂的分散效果优于阳离子和非离子表面活性剂。复合相变材料中添加质量分数为0.8%,十二烷基苯磺酸钠(SDBS)和质量分数为0.4%Fe₂O₃的体系,超声时间为80 min时,纳米Fe₂O₃在相变材料中的分散效果最好。添加纳米Fe₂O₃后复合蓄热相变材料的相变潜热及相变温度有所下降,热导率提高34.9%。300次热循环复合相变材料的相变温度波动区间不超过0.41℃,相变潜热波动区间不超过4.0%,热稳定性良好。     

石墨烯泡沫热物性与界面热导温度相关性研究

石墨烯泡沫是将石墨烯立体化形成的复合材料,在锂离子电池等领域有较好的应用前景,而其导热性质成为限制工业应用的重要因素。基于瞬态电热技术,研究了石墨烯泡沫的导热性质及其随温度的变化。结果表明,不同于Umklapp声子散射机理,石墨烯泡沫的热导率随温度呈正相关性:由室温至373 K时,热导率由0.71升高至1.10 W/(m·K)。分析发现,泡沫内部的大量界面是其低导热性质的主要因素。利用分子动力学模拟验证了石墨烯与基体材料间的界面传热随温度成正相关,与宏观材料测量结果相符。     

膨胀石墨/多壁碳纳米管基共晶盐复合相变材料的制备及热特性北大核心CSCD

单一水合盐作为相变蓄热材料使用时常常由于过冷、相分离、易泄漏以及其相变温度而受到限制,因此迫切需要制备出一种储热密度高、相变温度适宜、热导率大的复合相变材料。本工作采用熔融共混法在NH_(4)Al(SO_(4))_(2)·12H_(2)O(AASD)中掺入不同质量分数的MgSO_(4)·7H_(2)O(MSH),成功制备了AASD-MSH共晶盐相变材料,其质量比为55∶45,相变温度为76.4℃,相变潜热为189.4 J/g。共晶盐的X射线衍射图谱和傅里叶红外光谱表明其为物理混合。引入质量分数1%成核剂CaCl_(2)·2H_(2)O及1%增稠剂可溶性淀粉降低共晶盐过冷度,过冷度从34.9℃降低至28.0℃。引入改性膨胀石墨(MEG)与多壁碳纳米管(MWCNTs)制备复合相变材料,改善共晶盐易泄漏及热导率低等问题,当MWCNTs质量分数为0.5%时,复合相变材料的热导率高达8.185 W/(m·K),为共晶盐的19.98倍,其中共晶盐占比为75.6%,相变温度为74.3℃,相变焓值为133.5 J/g,过冷度进一步降低至22.2℃。热重实验表明与MEG-MWCNTs的复合增加了共晶盐的热稳定性,且经过100次冷热循环后复合相变材料的相变焓值基本不变,具有良好的循环稳定性。本工作制备得到的AASD-MSH/MEG-MWCNTs复合相变材料是一种相变温度适合、相变焓值较高、热导率较大的相变材料,且具有良好的热循环稳定性,应用潜力极大。     

Allotrope carbon materials in thermal interface materials and fuel cell applications: A review

The performance of allotrope carbon materials has been explored because of their superior properties in energy system applications. This review provides an understanding of the current work focusing on the applications of selected carbon materials in important energy systems, focus on thermal interface materials (TIMs), and fuel cell applications. This article begins with the introduction of TIMs and fuel cell in general working principle and presents details on carbon materials. The discussion focuses on updates from the latest research work and addresses current challenges and opportunities for research toward TIMs and fuel cell applications. The optimum performance of TIMs was seen when thermal conductivity achieved at a maximum of 3000 W (m K)⁻¹ by using vertically aligned carbon nanotubes (CNTs) and a minimum internal thermal resistance of 0.3 mm² K W⁻¹. Meanwhile for fuel cell, the platinum/CNTs catalyst applied proton exchange membrane fuel cell achieved high power density of 661 mW cm⁻² in the presence of Nafion electrolyte membrane. This review provides insights for scientists about the use of carbon materials, especially in energy system applications.     

Synthesis of supported Pt nanoparticles by sonication for ORR: Effect of the graphene oxide-carbon composite

Pt supported on graphene oxide (GO), reduced graphene oxide (RGO), carbon Vulcan (C) and GO-C composite were prepared by using sonication as a simple synthesis method in the absence of any special capping agent or thermal treatment. X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the materials synthesized. The electrocatalysts synthesized were evaluated for oxygen reduction reaction (ORR) in acid medium by using cyclic and linear voltammetry tests. The characterization results indicated that the highest dispersion of small Pt particles was observed on the samples supported on GO materials compared to carbon Vulcan due to the oxygen functional surface groups, which promoted a homogeneous distribution of Pt nanoparticles. The electrochemical characterization indicated that Pt/GO-C composite exhibited a 50% more specific and mass activity at 0.85 V for ORR than the conventional Pt/C catalysts, which is associated to Pt-support interaction that modifies the electronic properties of Pt for electrochemical application in fuel cell. GO-C (1:1) can be a promising support for improving the electrochemical activity for ORR.     

The effect of oxygen–containing functional groups on the H2 adsorption of graphene–based nanomaterials: experiment and theory

The oxygen–containing functional groups of graphene oxide (GO) play an important role in hydrogen storage. In addition to the contribution of the specific surface area and micro–porous porosity, the interactions of the functional groups with H₂ molecules are also an important factor in the aspect of GO hydrogen storage. This paper explores the oxygen–containing functional groups affecting the hydrogen physisorption capacity of the GO and reduced graphene oxide (RGO) by experimental H₂ adsorption measurement and theoretical calculation. Experimental results related to synthesis of GO and RGO via the modified Hummer's method and characterized using SEM, TEM, SAED, XRD, FTIR, TGA and Raman spectroscopy, are presented. Compared with RGO, the surface and edge of GO contain a large amount of oxygen–containing functional groups and its specific surface area is slightly increased through BET measurement. GO is found to exhibit better H₂ uptake capacity (0.74 wt%) as compared to RGO (0.47 wt%) at 77 K and pressure up to 10 bars. The density functional theory is applied to optimize the adsorption configurations of H₂ on the surface of samples. Calculation results show that the adsorption on the GO can be promoted by surface functional groups epoxy, hydroxyl, carboxyl and carbonyl; the enhancement of hydroxyl is greater than other species on the surface and the maximal adsorption energy reaches to ?0.112 eV which is about twice that of graphene. As indicated above, these functional groups could be formed easily on the graphene surface, which not only enhance specific surface area and interlayer spacing, but also significantly change the location of carbons, redistributing the electron structure of graphene and enhancing the adsorption energy.     

Enhanced oxygen evolution reaction activity of NiFe layered double hydroxide on nickel foam- reduced graphene oxide interfaces

Herein, we prepared a novel nickel iron-layered double hydroxide/reduced graphene oxide/nickel foam (NiFe-LDH/RGO/NF) electrodes by two step electrodeposition processes for oxygen evolution reaction (OER). The modification of NF by RGO increased the interface conductivity and electrochemical active surface areas (ECSA) of the electrode. The NiFe-LDH/RGO/NF electrode has shown higher catalytic activity with a lower overpotential of 150 mV at the current density of 10 mA cm⁻². The NiFe-LDH/RGO/NF electrode has also shown a small Tafel slope of 35 mV per decade due to the synergy effect between the larger ECSA and the conductive RGO interface. Furthermore, the electrodes exhibits almost 10 h stability under a general current density of 10 mA cm⁻².     

Thermal properties of particulate TIMs in squeeze flow

Direct numerical simulations based on a thermal Lattice–Boltzmann method are utilized to compute the effective thermal conductivity of particulate thermal interface materials (TIMs). By simulating the squeezing process, we obtain the particle distribution in a situation similar to application. Therefore, there is no need to calculate the average thermal characteristics from several pre-defined random distributions. The effects of particle volume fraction, particle size, and particle to matrix thermal conductivity ratio on the thermal performance are investigated. The results for the effective thermal conductivity are in agreement with the existing semi-analytical and experimental results reported in the literature.     

PtRu nanoalloys loaded on graphene and TiO2 nanotubes co-modified Ti wire as an active and stable methanol oxidation electrocatalyst

Highly active, durable and scalable fuel cell electrocatalysts are highly desirable but challenging. Herein, we first develop a novel catalyst of PtRu nanoalloys loaded on graphene modified anodic TiO₂ nanotubes arrays (TNTs) grown on flexible Ti wires (denoted as PtRu/RGO/TNTs). Electrodeposited reduced graphene oxide (RGO) is used to improve the electric conductivity and facilitate the dispersion of PtRu nanoparticles. TiO₂ nanotubes arrays could guarantee the large surface area, and PtRu nanoalloys are well-dispersed on the inner and external walls of the TNTs as well as the RGO surface, which could facilitate the fast mass transport and enhanced electrocatalytic activity. PtRu nanoalloys with intimate contact between the two metals is conductive to remove the harmful CO-like byproduct, resulting in superior tolerance to CO poisoning. In addition, this work first design and use the spirally flexible Ti wire electrode configuration in direct methanol fuel cell, which shows a highly efficient catalytic performance. Moreover, this kind of catalytic support is a strong candidate for other electrochemical energy conversion devices.     

Effect of graphene and its derivatives on thermo-mechanical properties of phase change materials and its applications: a comprehensive review

Phase change materials (PCMs) play a leading role in overcoming the growing need of advanced thermal management for the storage and release of thermal energy which is to be used for different solar applications. However, the effectiveness of PCMs is greatly affected by their poor thermal conductivity. Therefore, in the present review the progress made in deploying the graphene (Gr) in PCMs in the last decade for providing the solution to the aforementioned inadequacy is presented and discussed in detail. Gr and its derivatives ((Gr oxide (GO), Gr aerogel (GA) and Gr nanoplatelets (GNPs)) based PCMs can improve the thermal conductivity and shape stability, which may be attributed to the extra ordinary thermo-physical properties of Gr. Moreover, it is expected from this review that the advantages and disadvantages of using Gr nanoparticles provide a deep insight and help the researchers in finding out the exact basic properties and finally the applications of Gr can be enhanced.In this work, Gr and its derivatives based PCMs was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) by which crystal structure was known, phase was identified along with the knowledge of surface structure respectively. The increase in the mass fraction (%) of the filler (Gr and its derivatives) led to even better thermo-physical properties and thermal stability. The thermal characterization was also done by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and thermal conductivity tests. The enthalpy of freezing and melting showed that Gr and its derivatives based PCMs had a very high energy storage capability as reflected in its various applications.     

Hydrate salt/self-curing acrylic resin form-stable phase change materials with enhanced surface stability and thermal properties via the incorporation of graphene oxide

This work presents a novel eutectic hydrate salt/self-curing acrylic resin form-stable phase change materials (PCMs) composite (EHS/SCR) with favorable form-stable performances for heat energy storage. Further, to improve the surface stability, latent heat and thermal conductivity of the EHS/SCR particles, graphene oxide (GO) used as cladding materials is incorporated onto the surface of the EHS/SCR particles to prepare the GO modified EHS/SCR phase change composite (EGO). The obtained results indicate that the GO-targeted absorption model has achieved the enhancements in stability and thermal properties of EHS/SCR while making use of GO in an efficient and economical way. To be specific, with the introduction of GO of only 1.07 wt%, the thermal conductivity of 0.508 W/m·K is achieved, the value shows a significant rise of 128.6% compared with the EHS/SCR of 0.222 W/m·K. Additionally, the maximum latent heat of EGO-6 is up to 90.4 J/g, which exhibits a 3.19-fold increase compared against that of the uncoated EHS/SCR. Moreover, the prepared EGO composite PCM remain a good thermal cycling reliability after 300 thermal cycles. This work provides a novel opportunity to improve the performance of form-stable PCM composites with an intelligent manufacture-oriented pattern.