Single-Walled Carbon Nanotube-in-Binary-Polymer Nanofiber Structures and Their Use as Carbon Precursors for Electrochemical Applications

Hierarchical structuring of materials in the nanometer regime provides opportunities to achieve extraordinary characteristics of the resulting products. Here, we report unique one-dimensional hierarchical nanostructures consisting of single-walled carbon nanotubes (SWNTs), polyvinyl alcohol (PVA), and polyacrylonitrile (PAN). First, SWNT-in-binary-polymer nanofiber (SbPNF) structures were obtained through the incorporation of PVA-wrapped SWNTs into PAN, followed by the electrospinning of the SWNT/PVA/PAN solution. Importantly, the SbPNFs exhibited an aligned SWNT-in-nanofiber structure and enhanced ordering of the polymer chains. The SbPNFs were successfully converted to carbonized products [SWNT-in-carbon nanofibers (SbCNFs)] with enhanced crystallinity and tunable electrochemical properties. Compared to those of the control samples (no SWNT), the charge-transfer resistance and the surface area of the SbCNFs were two orders of magnitude lower and 11-20% higher, respectively, which resulted in better electrochemical properties. The major factors determining the properties of the SbCNFs included the SWNT content and PVA/PAN microphase behavior. Furthermore, the removal of the PVA phase from the SbPNFs provided another opportunity to control the textural properties of the carbonized products. It was found that meso- and macropores were more developed in the carbonized products (SCNFs). The specific capacitance of the SCNFs increased to a maximum of 577 F g(-1), which was 3.7 times higher than that of the SbCNFs. The SCNF with the best properties was successfully applied to electrochemical capacitors as the electrode material. It is believed that further optimization of the hierarchical nanostructures will impart attractive properties for various applications.