טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentPrilutsky Sabina
SubjectComposite Polymer Nanofibers with Carbon Nanotubes
DepartmentDepartment of Chemical Engineering
Supervisors Professor Yachin Cohen
Professor Eyal Zussman
Full Thesis textFull thesis text - English Version


Abstract

Carbon fibers (CFs) are one of the most successful products to be commercialized in the past years. The structure, and thus the properties of CFs strongly depend on the structure of the precursor fibers. Fabrication of precursor fibers by the electrospinning (ES) technique leads to the higher degree of crystallinity, modulus and strength of CFs, due to the strong elongation and thinning of precursor fibers in this process. Formation of nanocomposite materials in which a polymeric matrix is reinforced by carbon nanotubes (CNTs) is a promising way to translate the unique properties of CNTs to the macro scale. In this work carbon nanofibers (CNFs) were studied by carbonization of precursor composite nanofibers. These were made of poly(acrylonitrile) (PAN) reinforced with multiwalled CNTs (MWCNTs) by the ES technique. The main hypothesis was that the embedded MWCNTs in the PAN nanofibers may serve as nucleating centers for the carbonization process, leading to higher crystallinity of graphitic layers near the CNT, providing enhanced properties and function of the fabricated CNFs.

The morphology of the CNFs at different stages of its fabrication was characterized by transmission electron microscopy (TEM) and Raman spectroscopy. The polycrystalline nature of the CNFs was shown, with increasing of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results validated our assumption that embedded MWCNTs nucleate the growth of carbon crystals during PAN carbonization. Morphological development during the carbonization of composite CNFs characterized by TEM with in-situ heating have shown that the orientation of the graphitic structure does not appear to change significantly with time with constant temperature, except at the stage of 750°C, where noticeable enhancement was observed. The influence of stress application during the stabilization of precursor nanofibers shows enhancement of graphitic layer orientation with increasing of applied stress.

Electrodes made of carbonized PAN (cPAN) nanofibers, with and without embedded MWCNTs were evaluated as anodes in glucose fuel cell (FC) application. The effect of several characteristics, such as the presence of MWCNTs, polymer concentration in the solution and silver electroless plating on FC performance were measured The carbon electrodes were successful as anodes showing significant activity even without silver catalyst, with noticeable improvement by incorporation of MWCNTs. The orientation of graphitic layers and the coherence of layer packing were shown to be important for enhanced electrode activity. Electroless silver metallization of the carbon nanofiber electrodes leads to much better FC performance.