孔结构对煤基活性炭电极材料电化学性能的影响(英文)

以太西无烟煤为前驱体,NaOH为活化剂制备电化学电容器电极材料。采用N2吸附法及电化学测试对活性炭的孔结构和电化学性能进行了表征。在1mol/L(C2H5)4NBF4/碳酸丙烯酯有机电解液体系中,研究了孔结构对活性炭电极材料的电化学性能的影响。结果表明:以NaOH为活化剂可制备出比表面积943mol/L～2479mol/L、比电容57F/g～167F/g的活性炭电极材料。活性炭电极材料的比电容不仅取决比表面积,而且与活性炭的孔径分布有关。孔径为2nm～3nm的中孔的存在可以有效降低电解液的扩散阻力,提高电极材料比表面积的利用率,从而使电容器的电化学性能得到增强。     

丝瓜络基活性炭电极材料的制备及其电化学性能表征

以丝瓜络作为前驱体,KOH为活化剂,在不同温度下炭化、活化制备活性炭,并将其作为超级电容器电极材料。采用N2吸附及电化学测试对活性炭的孔结构和电化学性能进行了表征,研究了炭化温度、碱炭比对活性炭电极材料孔结构和电化学性能的影响。结果表明:丝瓜络经过一步炭化即可制备出电化学性能优异的炭材料,经过KOH活化后比电容明显增加,在碱炭比为2时制备活性炭的比表面积、总孔容分别达到1549m2/g和0.901cm3/g,比电容达到228F/g,是未活化炭化物比电容的2.5倍,是一种理想的电极材料。活性炭作为电极材料,其比表面积存在一个最佳值,孔的容积、大小和形状对电解质离子的储存、扩散有着重要作用,对电化学性能有很大影响。     

利用核桃壳制备高比表面积活性炭电极材料的研究

以核桃壳为原料,采用KOH活化法制备活性炭,并将其用作超级电容器电极材料。利用N2吸附和扫描电镜(SEM)表征活性炭的孔结构及表面形貌,系统研究碱炭比(KOH与核桃壳炭化料的质量比)对活性炭孔结构的影响,并采用恒流充放电及循环伏安等测定核桃壳活性炭电极材料在3mol/L KOH电解液中的电化学性能。结果表明,随着碱炭比的增大,活性炭的比表面积、总孔容及中孔比例先逐渐增大后稍有减小。当活化温度为800℃,活化时间为1h,碱炭比为4时,可制备出比表面积为2404m2/g,总孔容为1.344cm3/g,中孔比例为28.6%,孔径分布在0.7~3.0nm之间的高比表面积活性炭。该活性炭用作超级电容器电极材料具有良好的大电流放电特性和优异的循环性能,电流密度由50mA/g提高到5000mA/g时,其比电容由340F/g降低到288F/g,经1000次循环后,比电容保持率为93.4%。     

模板炭化法制备沥青基中孔炭材料

以MgO为模板,采用低软化点(27℃)各向同性沥青为炭材料前驱体,采用程序升温一步炭化法制得了系列中孔炭材料。采用乙酸镁和柠檬酸镁为MgO的前驱体,沥青与MgO前驱体按照不同质量比混合,混合比例以得到的MgO为计算基准。采用低温N2吸附测得炭材料的比表面积和孔径分布,采用透射电镜观察炭材料的内部结构特征。结果表明,两种前驱体与沥青混合得到的炭材料比表面积均随MgO/沥青质量比例的增加呈线性增加趋势,柠檬酸镁体系中MgO/沥青质量比为8/2时最高比表面积达到1295m2/g,随MgO/沥青质量比的不同分别在2.5nm和5nm处有集中的孔分布;乙酸镁体系制得的炭最高比表面积也达到1199m2/g,并且在5nm和12nm处有集中的孔分布。     

预炭化对KOH活化石油焦的结构及电容性能的影响

以不同温度炭化的石油焦为原料、KOH为活化剂制备电化学电容器用炭电极材料. 采用XRD、TEM和N₂吸附法对前驱体及活化产物的结构进行了表征, 并考察了样品的电化学性能. 结果表明: 通过调整前驱体的预炭化温度, 可实现对石油焦基活性炭的微晶结构和孔结构的调控, 分别制得无晶体特性的高比表面积活性炭和由大量类石墨微晶构成的低比表面积活性炭. 低表面积活性炭依靠充电过程中电解质离子嵌入类石墨微晶层间而实现能量存储, 具有比高比面积活性炭高10倍的面积比电容和更大的体积比电容.     

炭化温度对酚醛树脂基活性炭孔结构及电化学性能的影响研究

以酚醛树脂为炭前驱体,KOH作活化剂,通过调节炭化温度在相同活化条件下制备了具有不同孔隙结构的活性炭材料.N_2吸附测试表明随着炭化温度降低,活性炭材料比表面积先增大后减小,孔容则不断增大.其中,550℃炭化样品与KOH反应活性最佳,可制得比表面积为2983m~2/g,总孔容为1.58cm~3/g,中孔孔容达到0.59cm~3/g的活性炭材料.采用直流充放电法、交流阻抗法和循环伏安法测定以上述多孔炭为电极材料的双电层电容器的电化学性能,结果表明,PF550活性炭材料电容性能最佳,在有机电解液中100mA/g充放电时,比电容达到160F/g,电流密度增大50倍容量保持率达到82%,显示出良好的功率特性;活性炭材料中存在一定比例的中孔不仅可以改善电极材料的功率特性,而且可以提高微孔的利用率.     

微波法煤基活性炭的制备及其电化学性能研究

以内蒙古优质褐煤为原料,KOH为活化剂,采用微波加热活化法制备超级电容器用活性炭,利用低温氮气吸附及恒流充放电、循环伏安等方法测定活性炭的孔结构及其用作电极材料的电化学性能,并与日本商业化超级电容器用活性炭在结构及性能方面进行对比分析。结果表明,在碱炭比为3,微波活化时间为20min的条件下,可制备出比表面积达2593m2/g、总孔容达1.685cm3/g、孔径主要分布在0.5～10nm之间、中孔率达67.3%、平均孔径为2.61nm的优质活性炭。该活性炭用作超级电容器电极材料在3mol/L KOH电解液中具有优异的电化学性能,电流密度由50mA/g提高到10A/g时,其比电容由346F/g降低到273F/g,显示出良好的功率特性,经1000次循环后,比电容保持率为93.2%。与商业活性炭相比,微波法活性炭的性能更加优良。     

针状焦基活性炭的制备及其作为EDLCs电极材料的电化学性能

以针状焦生焦为原料,通过KOH化学活化法,在不同活化条件下制备出一系列高比表面积活性炭,并对这些活性炭进行了孔结构表征.而后以30 % KOH溶液为电解液,测试了由所获活性炭制备的一系列电极的电双层电容性能.结果表明：在碱炭比7：1、活化温度850 ℃时,所制活性炭的BET比表面积为2 728 m^2/g,孔容为2.14 cm^3/g,统计平均孔径为4.4 nm,大中孔孔容占总孔孔容约50 %.该活性炭电极的比电容达305 F/g,有相对较高的能量密度、良好的功率特性以及双电层电容特性.     

柚子皮基层次孔炭的制备及电化学性能

以柚子皮水热炭为前驱体,KOH为活化剂,800℃活化制备层次孔炭电极材料。采用扫描电子显微镜(SEM)、N2吸附法对活性炭的表面形貌和孔结构进行了表征,并评价了其在无机电解液体系(3mol/L KOH)中的电化学性能。结果表明,碱碳比为1∶1时制备的活性炭呈蜂窝状结构,其比表面积、总孔容分别达到1421 m2/g和0.7626cm3/g,相应的电极材料具有典型的双电层电容特性,质量比电容和体积比电容分别达到226F/g和250F/cm3(电极片密度为1.1g/cm3),1000次循环之后电容保持率达到91.45%。与柚子皮直接活化制备的电极材料相比,质量比电容和体积比电容分别增加了31.40%和37.36%。     

废茶叶基活性炭的制备及其电化学性能研究

以废茶叶的炭化料为前驱体,KOH为活化剂(碱炭比1∶1、2∶1、3∶1),在800℃下活化1h制备双电层电容器用活性炭电极材料。利用扫描电镜、低温N2吸附对活性炭的形貌、孔结构进行表征,采用恒流充放电、循环伏安和交流阻抗等测试方法评价其在3mol/L KOH电解液中的电化学性能。结果表明,3种活性炭比表面积、总孔容和中孔率最高分别达1 900m2/g、0.919 4cm3/g和35.7%;3种活性炭电极材料在0.055 6 A/g电流密度下的比电容分别为202F/g、255F/g、194F/g,电流密度增加到2.780A/g时,电容保持率分别为84.2%、67.1%、86.6%;等效串联电阻仅为0.10~0.12Ω;在碱碳比为2∶1时制备的活性炭电极材料在2.363A/g下比电容为148F/g,经1 000次循环充放电后,其质量比电容为147.7F/g,电容保持率高达99.3%。     

Kinetics of chemical vapor infiltration of carbon nanofiber-reinforced carbon/carbon composites

Preforms containing 0, 5, 10, 15 and 20 wt.% carbon nanofibers (CNFs) were fabricated by spreading layers of carbon cloth, and infiltrated by using the technique of isothermal chemical vapor infiltration (ICVI) at the temperature of 1100 °C under the total pressure of 1 kPa and with the flow of the mixture of propane/nitrogen in a ratio of 13:1. The infiltration rates increased with the rising of CNF content, and after 580 h of infiltration, the achievable degree of pore filling was the highest when the CNF content was 5 wt.%, but the composite could not be densified efficiently as the CNF content ranged from 10 to 20 wt.%. An analysis of the results, based on the effective diffusion coefficient and on the in-pore deposition rates, shows that the CNFs, due to their higher aspect ratio, accelerate overgrowth at pore entrances and thus lead to incomplete pore filling.     

Graphitization behaviour of carbon fibre-glassy carbon composites

Carbon fibre-carbon composites were fabricated by aligning PAN-based carbon fibre unidirectionally in furfuryl alcohol resin char. The graphitization behaviour was investigated by an X-ray diffraction technique and by the measurement of magnetoresistance. The time-temperature superimposition study for interlayer spacing resulted in an activation energy of 242±35 kcal mol⁻¹. The kinetic study on magnetoresistance agreed with the result of X-ray measurement. The activation energy is that for the graphitization of the layer structure formed in the glassy carbon matrix of the composites. The graphitization mechanism of the layer structure is the same as that of soft carbons.     

短切炭纤维增强沥青基C/C复合材料的组织特征

利用新型、高效的模压半炭化成型工艺，在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料制品，并借助光学显做镜和扫描电镜对其微观组织和断口形貌进行了观察。通过分析，解释了短切炭纤维增强沥青基C／C复合材料中炭纤维损伤的形成机制，提出了作为增强体相的短切炭纤维和焦炭颗粒与基体炭之间独特的界而结构模型。研究还表明：复合材料中明显存在着基体相和颗粒相一基体相的显微结构不仅呈层片状，而且层片状的结构好像数层桔子皮，将颗粒相包裹起来，这种“桔皮包裹”式的结构与炭纤维表面的POG结构基本相似。     

短切炭纤维增强沥青基C/C复合材料的力学性能

利用模压半炭化成型工艺在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料（简称SCFRC）。研究了短切炭纤维的体积分数对SCFRC材料的体积密度和力学性能的影响规律。借助光学显微镜和扫描电镜对其微观组织和断口形貌进行了观察，分析了短切炭纤维对SCFRC材料的增强机制。结果表明，当短切炭纤维的体积分数由0％增大到11．8％时，SCFRC材料的力学性能随之呈线性增加；短切炭纤维增强SCFRC材料的机制主要有裂纹偏转效应、桥联效应以及脱粘和拔出效应。     

软硬混编预制体增强沥青基4D-C/C材料的拉伸破坏行为

以X-Y平面依次铺设炭纤维束、Z向穿插炭棒的4D软硬混编为预制体,采用沥青液相常压、高压浸渍/炭化-石墨化循环致密工艺制备4D-C/C复合材料。通过该材料Z向(炭棒方向)的拉伸实验,测定其拉伸性能和力学行为,并采用SEM分析试样表面及断口形貌。结果表明:宏观上拉伸试样以炭棒整体拔出的形式破坏;细观尺度上,试样表面形成了与载荷方向垂直的贯穿性裂纹,裂纹以2 mm左右的距离呈等间距分布;材料进一步的破坏过程中,基体裂纹在X-Y向纤维束中呈线性扩展,快速分割了基体材料,使4D-C/C复合材料的拉伸破坏演变为1D-C/C复合材料的破坏模式,由于炭棒与基体炭界面结合弱,炭棒以拔出方式失效和破坏。     

Mesoscale evolution of non-graphitizing pyrolytic carbon in aligned carbon nanotube carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high-strength low-density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano- and mesoscale structural evolution of phenol-formaldehyde-derived PyCs is established as a function of pyrolysis temperature (\(T_{\mathrm {p}}\)) using X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Aligned CNT PyC matrix nanocomposites are found to evolve faster at the mesoscale by plateauing in crystallite size at \(T_{\mathrm {p}}\) \(\sim\)800 \(^{\circ }\hbox {C}\), which is more than \(200\,\,^{\circ }\hbox {C}\) below that of unconfined PyCs. Since the aligned CNTs used here exhibit \(\sim\)80 nm average separations and \(\sim\)8 nm diameters, confinement effects are surprisingly not found to influence PyC structure on the atomic-scale at \(T_{\mathrm {p}}\) \(\le \)1400 \(^{\circ }\hbox {C}\). Since CNT confinement could lead to anisotropic crystallite growth in PyCs synthesized below \(\sim\)1000 \(^{\circ }\hbox {C}\), and recent modeling indicates that more slender crystallites increase PyC hardness, these results inform fabrication of PyC-based meta-materials with unrivaled specific mechanical properties.     

Activated carbon catalyzing the formation of carbon nanotubes

Activated carbon (AC), a common carbon material, is employed as catalyst to synthesize carbon nanotubes (CNTs) through chemical vapor deposition (CVD) and detonation-assisted CVD methods. The results show AC can effectively catalyze CNT formation. From the microscopic observations on morphologies and structures of the formed intermediates, it is found that carbon-catalyzed CNT formation follows particle-wire-tube stepwise evolution mechanism, in which carbon nanoparticles first assemble into wire-like nanostructures, then evolve into nanotubes via particle-particle coalescence and structural crystallization.     

Biodistribution of carbon single-wall carbon nanotubes in mice

Carbon nanotubes are promising for use in biomedical and pharmaceutical sciences. Therefore, it becomes imperative to know the basic biological properties of carbon nanotubes in vivo. We labeled the water-soluble hydroxylated carbon single-wall nanotubes with radioactive 125I atoms, and then the tracer was used to study the distribution of hydroxylated carbon single-wall nanotubes in mice. They moved easily among the compartments and tissues of the body, behaving as small active molecules though their apparent mean molecular weight is tremendously large. This study, for the first time, affords a quantitative analysis of carbon nanotubes accumulated in animal tissues.     

Vitreous joining of SiC-coated carbon/carbon composites

This paper investigated the feasibility of joining of carbon/carbon (C/C) composites by using a silicate as interlayer. A SiC coating was pre-prepared on C/C substrate by pack-cementation technique to improve the wettability of glass on C/C composites, then the joints were prepared by a one-shot and low cost way. Microstructure and morphologies of the as-received joints were characterized by XRD, SEM and EDS. The results indicated that the SiC coating not only had a strong bonding with C/C composites, but also had a good physical and chemical compatibility with silicate glass. The room-temperature shear strength of the joints gives encouraging results, which can be up to 26 MPa. The fracture mode and the fracture behavior were discussed also.