Activated carbon from coconut leaves for electrical double-layer capacitor

This study investigates the potential of coconut leaves as a precursor to obtain activated carbon. Coconut leaf-activated carbon (CLAC) has been prepared through gas activation process starting with carbonization at 400 °C in nitrogen flow for 3 h. The carbonized coconut leaves were milled using planetary ball milling followed by activation with carbon dioxide (CO₂) at different temperatures ranging from 700 to 1000 °C. The Brunauer–Emmett–Teller (BET) characterization reveals that the surface area of CLACs increases with the increase in activation temperature. Electrodes prepared from CLACs have been used to fabricate electrochemical double-layer capacitors (EDLCs) in order to study the electrochemical behavior using galvanostatic charge–discharge measurements and cyclic voltammetry. The carbon activated at 900 °C delivered the best specific capacitance of 133.4 F/g at current density of 200 mA/g.     

Preparation of vertically aligned carbon nanotube arrays grown onto carbon fiber fabric and evaluating its wettability on effect of composite

Vertically aligned carbon nanotube (CNT) arrays have been grown onto the carbon fiber fabric using a catalytic chemical vapor deposition (CCVD) method. The as-synthesized CNT arrays are about 20 μm in height, and the nanotube has a mean inner and outer diameter of 2.6 nm, 5.5 nm, respectively. The CNT-grafted carbon fabric shows a hydrophobic property with a contact angle over 145°, and the single CNT-grafted carbon fiber shows a sharp increase of dynamic contact angle in de-ionized water from original 71.70° to about 103°, but a little increase does in diiodomethane or E-51 epoxy resin. However, the total surface energy of carbon nanotube-grafted carbon fiber is almost as same as that of as-received carbon fiber. After CNTs growth, single fiber tensile tests indicated a slight tensile strength degradation within 10% for all different lengths of fibers, while the fiber modulus has not been significantly damaged. Compared with the as-received carbon fibers, a nearly 110% increase of interfacial shear strength (IFSS) from 65 to 135 MPa has been identified by single fiber pull-out tests for the micro-droplet composite, which is reinforced by as-received carbon fiber or CNT-grafted carbon fiber.     

Phase-contrast X-ray imaging of the gas diffusion layer of fuel cells

The understanding of and in situ observation of the transport and distribution of water in carbon‐paper gas diffusion layers (GDLs) using non‐destructive imaging techniques is critical for achieving high performance in polymer electrolyte fuel cells (PEFCs). To investigate the behavior of water in GDLs of PEFCs, phase‐contrast X‐ray imaging via X‐ray interferometric imaging (XII) and diffraction‐enhanced imaging (DEI) were performed using 35 keV X‐rays. The XII technique is useful for the radiographic imaging of GDLs and in situ observations of water evolution processes in operating PEFCs. DEI provides a way for tomographic imaging of GDLs in PEFCs. Because high‐energy X‐rays are applicable to the imaging of both carbon papers and heavy materials, which make up PEFCs, phase‐contrast X‐ray imaging techniques have proven to be valuable for investigation of GDLs.     

Preparation of anti-oxidative carbon fiber at high temperature

In this paper, carbon fibers with improved thermal stability and oxidation resistive properties were prepared and evaluated their physical performances under oxidation condition. Carbon fibers were coated with SiC particles dispersed in a polyacrylonitrile solution and then followed by pyrolyzed at 1400 °C to obtain the SiC nanoparticle deposition on the surface of the carbon fiber. The SiC coated carbon fiber showed extended oxidation resistive property as remaining 80-88% of the original weight even at high temperature 1000 °C under air, as compared with the control of zero weight at 600 °C. The effects of the coating conditions on the oxidation resistive properties of the coated fibers were studied in detail.     

Effects of plasma surface modification on the mechanical properties of carbon fiber and carbon fiber/epoxy composite

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.     

Double layer oxidation resistant coating for carbon fiber reinforced silicon carbide matrix composites

Double layer coatings, with celsian-Y₂SiO₅ as inner layer and Y₂Si₂O₇ as outer layer, were prepared by microwave sintering on the surface of carbon fiber reinforced silicon carbide matrix composite. Both celsian, Y₂SiO₅ and Y₂Si₂O₇ were synthesized by in situ method using BAS glass, Y₂O₃ and SiO₂ as staring materials. The sintering temperature was 1500 °C, and little damage was induced to the composite. The composition and micrograph of the fired coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The oxidation and thermal shock resistance of samples with doubled-layered coating were characterized at 1400 °C in air. After 150 min oxidation and thermal cycling between 1400 °C and room temperature for 15 times, the weight loss of double layer-coated sample was 1.22% and there were no cracks in the coating.     

低温泵用椰基活性炭材料的选择和比较

为了选择用于核聚变研究领域中在氢、氦气环境下的低温吸附泵所用的吸附剂,在初步筛选基础上,比对了4种椰基活性炭材料。采用扫描电镜对材料微观结构进行了扫描,用比表面积及孔径分析仪测定了等温吸附性能,最终获得了活性炭样本的比表面积、微孔比表面积份额、不同孔径所对应的孔容等性能数据;通过对实验结果的比对分析,为筛选适用于核聚变研究环境下低温吸附泵使用的吸附剂材料,提供了重要的实验数据。     

低温吸附泵用椰壳活性炭的性能测试

活性炭的比表面积、孔径及分布是影响液氦低温吸附泵抽氢、氦性能的关键因素。为了确定制作液氦低温吸附泵的吸附剂,选取了C1、C2、C3、C4四种椰壳活性炭,用比表面积及孔径分析仪测定了其等温吸附性能,并对实验数据进行了针对性分析,获得了各活性炭的比表面积、微孔比表面积份额、不同孔径所对应的孔容等性能数据。结果表明,四种活性炭中C2最适于做为抽氢、氦的液氦低温吸附泵的吸附剂。     

碳纤维复合材料内部缺陷深度的定量红外检测

利用脉冲红外热成像技术对碳纤维复合材料试件内部的模拟脱黏缺陷的深度进行测量, 研究在被测物热属性参数未知情况下,碳纤维增强塑料中缺陷深度的测量方法. 分析了平板材料在脉冲热源激励下的一维热传导模型;给出了内部缺陷深度的红外测量原理; 选用对数温度二阶微分峰值时刻作为特征时间测量缺陷深度; 考虑单点标定测量深度可能产生较大的随机误差,提出利用最小二乘法多项式拟合建立阶梯件中阶梯深度与其对应的对数温度时间二阶微分曲线峰值时间两者之间的标定关系式的方法, 选择在相对误差平方和最小情形下的拟合关系式作为脱黏缺陷深度测量的标定关系式. 实验结果表明,利用该方法测量脱黏缺陷深度的精度优于单点法标定测量结果, 实现了在被检测材料热属性参数未知的情况下仍能较准确地测量脱黏缺陷深度.     

Creep and physical aging in a polyamideimide carbon fiber composite

The creep properties of an amorphous thermoplastic polyamideimide and its continuous carbon fiber composite have been investigated. Creep behavior in the viscoelastic (low stress) and viscoplastic (high stress) ranges was examined. The interaction of physical aging with the creep behavior of the material was found to be significant in both stress regimens. Physical aging shifted creep curves to longer times in the viscoelastic range, reducing the total amount of creep strain in both the viscoelastic and viscoplastic ranges. The amount of nonrecoverable strain produced during viscoplastic creep was highly dependent upon the amount of time a sample was held under load due to concurrent physical aging. Specimens aged significantly prior to testing showed no undue time dependence in the amount of nonrecoverable creep strain produced. The viscoplastic creep behavior was shown to be composed of instantaneous localized plastic deformation, viscous strain, stiffening due to aging, and densification due to aging.     

Characterisation of wettability in gas diffusion layer in proton exchange membrane fuel cells

This paper presents a detailed study of the wetting properties of three fuel cell gas diffusion layers (GDLs) having different morphologies and different contents of hydrophobic agent. An internal contact angle to water at temperature representative of PEM fuel cell operating conditions was directly obtained using the Washburn method with 66 ° C water as test liquid. These results show that the surface of the carbon fibres is hydrophilic under fuel cell operating conditions. Surface energy values of the GDL fibres, determined by a combination of the Washburn method and the Owens-Wendt two parameters theory, were found to be low, indicating that GDLs are wet very poorly by most liquids. About 40% of the total surface free energy values was related to a polar component allowing dipole-dipole and hydrogen bonding interactions with water. The origin of this polar character is discussed.     

Novel hole transport layer of nickel oxide composite with carbon for high-performance perovskite solar cells

A depth behavioral understanding for each layer in perovskite solar cells(PSCs)and their interfacial interactions as a whole has been emerged for further enhancement in power conversion efficiency(PCE).Herein,NiO@Carbon was not only simulated as a hole transport layer but also as a counter electrode at the same time in the planar heterojunction based PSCs with the program wx AMPS(analysis of microelectronic and photonic structures)-1D.Simulation results revealed a high dependence of PCE on the effect of band offset between hole transport material(HTM)and perovskite layers.Meanwhile,the valence band offset(?E_v)of NiO-HTM was optimized to be -0.1 to -0.3 eV lower than that of the perovskite layer.Additionally,a barrier cliff was identified to significantly influence the hole extraction at the HTM/absorber interface.Conversely,the ?E_v between the active material and NiO@Carbon-HTM was derived to be -0.15 to 0.15 eV with an enhanced efficiency from 15% to 16%.     

Controlled water flooding of polymer electrolyte fuel cells applying superhydrophobic gas diffusion layer

Water transport is critical to the successful implementation of polymer electrolyte fuel cells (PEFC), especially in long-term and dynamic operation in automotives. Liquid water appears in the fuel cells not only from the water generated at the cathode catalyst layer but also as a result of condensation of water vapor from the humidified gases. In this study, we report a simple approach to prepare a superhydrophobic gas diffusion layer by chemical vapor deposition of polydimethylsiloxane without significant change in pore size of gas diffusion layer unlike other approach adding hydrophobic agent such as polytetrafluoroethylene. A superhydrophobic coating on the GDL can be obtained, leading to exceptionally enhanced power performance and stability of PEFC especially at a high current where water transport becomes more critical.     

Preparation of microporous activated carbon and its electrochemical performance for electric double layer capacitor

Microporous activated carbons were prepared by microwave heating petroleum coke with potassium hydroxide as activation agent. Microporous activated carbons were characterized by infrared spectroscopy, X-ray diffraction and nitrogen adsorption/desorption isotherms. Electrochemical properties of an electric double layer capacitor using microporous activated carbon as electrode materials were investigated by constant current charge-discharge and electrochemical impedance spectroscopic techniques. The results show that the specific surface area and the pore volume of microporous activated carbon increase with increasing activation time before the activation time reaches 37 min. The microporous volume totals 94.0% in the microporous activated carbons and the average pore diameter of microporous activated carbon is 2.00 nm. Microporous activated carbons prepared in the activation time of 31, 35 and 37 min are named as AC-31, AC-35 and AC-37, respectively. Compared with AC-27 electrode, the internal resistance for ions transferring in AC-31, AC-35 or AC-37 electrode is relatively small. The specific capacitance of AC-31 is the biggest among the microporous activated carbons, and it retains 279.6 F g^?1 maintaining 93.5% capacity after 200 recycling number.     

切向气流作用下玻璃纤维复合材料的激光辐照效应

实验研究了样品表面有切向空气气流、切向氮气气流和无气流时,976 nm连续激光对玻璃纤维增强E-51环氧树脂复合材料的辐照效应。结果表明:无气流时,喷出的热分解产物会对入射激光产生屏蔽作用;有气流时,激光对玻璃纤维的破坏方式是其升温熔化后再被切向气流带走;当激光功率密度较低时,切向空气气流以加强样品表面的对流冷却作用为主,不利于激光对玻璃纤维复合材料的破坏;当激光功率密度较高时,切向空气气流以降低屏蔽作用和提供氧气助燃为主,有利于激光对玻璃纤维复合材料的破坏。三种气流状态下,质量损失随功率密度呈现单调增加趋势,当入射激光功率密度在100~600 W/cm2范围内,随着功率密度的增大,激光能量的利用效率逐渐增大并趋于稳定。     

切向气流作用下玻璃纤维复合材料的激光辐照效应

实验研究了样品表面有切向空气气流、切向氮气气流和无气流时,976 nm连续激光对玻璃纤维增强E-51环氧树脂复合材料的辐照效应。结果表明:无气流时,喷出的热分解产物会对入射激光产生屏蔽作用;有气流时,激光对玻璃纤维的破坏方式是其升温熔化后再被切向气流带走;当激光功率密度较低时,切向空气气流以加强样品表面的对流冷却作用为主,不利于激光对玻璃纤维复合材料的破坏;当激光功率密度较高时,切向空气气流以降低屏蔽作用和提供氧气助燃为主,有利于激光对玻璃纤维复合材料的破坏。三种气流状态下,质量损失随功率密度呈现单调增加趋势,当入射激光功率密度在100~600 W/cm2范围内,随着功率密度的增大,激光能量的利用效率逐渐增大并趋于稳定。     

Breakthrough/drainage pressures and X-ray water visualization in gas diffusion layer of PEMFC

The primary role of the gas diffusion layers (GDLs) in polymer electrolyte membrane fuel cells (PEMFC) is to maintain the delicate balance between water retention and removal in GDLs. Water management in the fuel cell is related to the breakthrough pressure at which water starts to pass through GDL, and the drainage pressure, which is maintained after the breakthrough. These pressures are both related to water management in fuel cells. Here we measured these pressures for two different GDLs and used X-ray tomography to visualize the water distributions within them. We then relate the variations in liquid pressures to the visualization and discuss water management in PEMFC.     

石蜡填充碳纳米管复合材料的制备与界面传热性能研究

以石蜡和经硝酸处理过的碳纳米管(CNTs)为原料,苯为溶剂,采用真空渗透法制备了石蜡填充CNTs纳米胶囊复合材料,并设计了一个简易的热界面装置,对石蜡填充CNTs材料在电子设备热管理中的应用能力进行了测试。结果表明:石蜡成功填充到CNTs管内,且在CNTs管外基本没有残留的石蜡。在传热界面未涂抹二甲基硅油时,内外两侧最高温度的温差为4.7℃,而分别涂抹二甲基硅油、未经酸处理(20%)CNTs/二甲基硅油、酸处理后(20%)CNTs/二甲基硅油、(20%)石蜡填充CNTs/二甲基硅油时,其内外两侧最高温度的温差分别为3.8℃,3.1℃,3.1℃,2.2℃,说明将石蜡填充CNTs作为二甲基硅油中的散热填充物具有更好的散热效果,且增加了界面间的热反应速度和热稳定性。     

Intense electron emission from carbon fiber cathodes

We studied the emission properties of carbon fiber cathodes. These cathodes were made either of a single carbon fiber or of carbon fabric, or of an array of carbon fiber bundles. It was found that an intense emission of electrons occurs from a plasma which is formed on the carbon fiber surface as a result of a flashover process. In addition, the time delay in the appearance of the electron emission with respect to the start of the accelerating voltage pulse was found to depend strongly on the voltage growth rate. A simple model of the plasma formation is suggested. Received 12 March 2001     

Electrocatalysis of oxygen reduction reaction on Nafion/platinum/gas diffusion layer electrode for PEM fuel cell

In this work a new membrane electrode based on Pt-coated Nafion membrane was fabricated. Chemical deposition process was used to coat platinum on Nafion 117 membrane and then Pt-coated Nafion membrane was hot pressed on gas diffusion layer (GDL) to make new membrane electrode. The electrochemical and chemical studies of the Pt-coated Nafions were investigated by electrochemical techniques, X-ray diffraction and scanning electron microscopy. The electrochemical results indicated that as the concentration of H₂PtCl₆ increased, the oxygen reduction reaction rate increased until the concentration was reached where the reduction reaction was limited by the problem of mass transport. The electrochemical results for oxygen reduction reaction showed that the new electrode which prepared by plating Nafion membrane with 0.06 M H₂PtCl₆ in electroless plating solution, has a higher performance than other electrodes. The XRD results showed that the average platinum particle size of the best sample was about 3 nm. The loading of platinum for this electrode was 0.153 mg cm⁻².