B Ali A, Renz F, Koch J, Tegenkamp C, Sindelar R
Institut für Anorganische Chemie, Leibniz Universität Hannover, Callinstr. 7, 30167 Hannover, Germany.
Hannover School for Nanotechnology, Laboratorium für Nano und Quantenengineering (LNQE), Leibniz Universität Hannover, Schneiderberg 39, 30167 Hannover, Germany.
Nanomaterials (Basel). 2020 Feb 18;10(2):351. doi: 10.3390/nano10020351.
Improving the graphitic structure in carbon nanofibers (CNFs) is important for exploiting their potential in mechanical, electrical and electrochemical applications. Typically, the synthesis of carbon fibers with a highly graphitized structure demands a high temperature of almost 2500 °C. Furthermore, to achieve an improved graphitic structure, the stabilization of a precursor fiber has to be assisted by the presence of tension in order to enhance the molecular orientation. Keeping this in view, herein we report on the fabrication of graphene nanoplatelets (GNPs) doped carbon nanofibers using electrospinning followed by oxidative stabilization and carbonization. The effect of doping GNPs on the graphitic structure was investigated by carbonizing them at various temperatures (1000 °C, 1200 °C, 1500 °C and 1700 °C). Additionally, a stabilization was achieved with and without constant creep stress (only shrinkage stress) for both pristine and doped precursor nanofibers, which were eventually carbonized at 1700 °C. Our findings reveal that the GNPs doping results in improving the graphitic structure of polyacrylonitrile (PAN). Further, in addition to the templating effect during the nucleation and growth of graphitic crystals, the GNPs encapsulated in the PAN nanofiber matrix act in-situ as micro clamp units performing the anchoring function by preventing the loss of molecular orientation during the stabilization stage, when no external tension is applied to nanofiber mats. The templating effect of the entire graphitization process is reflected by an increased electrical conductivity along the fibers. Simultaneously, the electrical anisotropy is reduced, i.e., the GNPs provide effective pathways with improved conductivity acting like bridges between the nanofibers resulting in an improved conductivity across the fiber direction compared to the pristine PAN system.
改善碳纳米纤维（CNF）中的石墨结构对于挖掘其在机械、电气和电化学应用方面的潜力至关重要。通常，合成具有高度石墨化结构的碳纤维需要近2500°C的高温。此外，为了实现改进的石墨结构，前驱体纤维的稳定化必须借助张力来增强分子取向。鉴于此，我们在此报告了使用静电纺丝，随后进行氧化稳定化和碳化来制备石墨烯纳米片（GNP）掺杂碳纳米纤维的方法。通过在不同温度（1000°C、1200°C、1500°C和1700°C）下对其进行碳化，研究了掺杂GNP对石墨结构的影响。此外，对原始和掺杂的前驱体纳米纤维在有和没有恒定蠕变应力（仅收缩应力）的情况下都实现了稳定化，最终在1700°C下进行碳化。我们的研究结果表明，GNP掺杂可改善聚丙烯腈（PAN）的石墨结构。此外，除了在石墨晶体成核和生长过程中的模板效应外，封装在PAN纳米纤维基质中的GNP在原位充当微夹单元，在不对纳米纤维毡施加外部张力的稳定化阶段，通过防止分子取向的丧失来发挥锚固功能。整个石墨化过程的模板效应通过沿纤维方向电导率的增加得以体现。同时，电各向异性降低，即GNP提供了具有改善导电性的有效路径，就像纳米纤维之间的桥梁一样，与原始PAN系统相比，导致纤维方向上的导电性得到改善。
