Recent Research Results On Carbon Nanofiber Porosity And Electronic Structure Control

Porous carbon nanofibers have abundant pore and electronic structure. They not only have small size effect, excellent heat resistance and chemical stability of inorganic nanomaterials, but also form self-supporting thin films, avoiding the defects of increasing interfacial resistance and decreasing mass transfer efficiency due to the use of adhesives, thus playing a great role in energy, sensing, environment and other fields.

At present, the main methods of preparing porous carbon nanofibers are activation method and template method. The activation method is mainly used to etch carbon nanofibers with KOH or HNO3 etch. The template method is mainly to form porous carbon fibers in situ by calcining mixtures of asphalt or polyacrylonitrile and pore forming agents. However, the activation method is usually complex and has pollution and safety problems, and the template method requires a large number of organic solvents. In addition, the porosity and electrical conductivity of carbon nanofibers prepared by these two methods are low. On the one hand, in order to ensure the integrity of the carbon nanofiber membrane structure, the porosity of most porous carbon nanofibers is less than 20%. On the other hand, the conductivity of these porous carbon nanofibers is usually less than 10 s/cm. Therefore, how to maintain the integrity of porous carbon nanofiber membrane and improve its porosity and conductivity is a challenge.

Based on this problem, the nanofiber research team led by Yu Jianyong, academician of Donghua University Textile Science and technology innovation center and Ding Bin researcher has made important progress in the research field of pore structure and electronic structure regulation of flexible carbon nanofibers. The related results are published in "Multifunctional Flexible Membranes from Sponge-Like Porous Carbon Nanofibers with High Conductivity" on the basis of sponge porous carbon nanofibers.

The research team has developed a flexible porous carbon nanofiber membrane with high porosity and high electrical conductivity based on the electrospinning method of the water system and the macro micro dual phase separation technology. In this study, the homogeneous mixing of carbon precursors and pore forming agents is the key factor to control porosity and electrical conductivity. Polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE) particles and boric acid (BA) were used as carbon precursors, macroporous inducers, crosslinking agents and microporous inducers respectively. BA was chemically crosslinked with PVA and PTFE to form a stable PVA-BA-PTFE sol, which avoided the self entanglement of PVA macromolecules. In the pre oxidation process at 280 C, PVA dehydrogenated to form a conjugated C = C bond, which improved the stability of the primary fibers. In N2, after high temperature pyrolysis, three carbon doped carbon nanofibers with high flexibility and high conductivity were formed. The continuous carbon skeleton in porous porous carbon nanofibers provides a fast channel for electron conduction, while the three pore structure (macroporous mesoporous microporous, porosity higher than 80%) reduces the transmission resistance of ions, molecules and particles. Therefore, it shows versatile properties in gas adsorption, sewage treatment, liquid storage, supercapacitors and batteries. For example, the fiber membrane has higher liquid storage capacity and faster methylene blue dye adsorption capacity. The carbon symmetric supercapacitor prepared by this fiber membrane has higher power density (3.9 kW/kg) and energy density (42.8 Wh/kg). When used as sulfur electrode, the capacity of lithium sulfur battery can reach 1200mAh/g under the condition of 1C current charge and discharge.