Electrospining: Preparation of novel highly conductive copper core-shell carbon nanofibers by coaxial electrospinning

Background

Over the past few decades, carbon nanofibers (CNFs) have gained tremendous academic and industrial importance due to their comprehensive properties, such as mechanical, thermal, and electronic properties. CNFs also have unique one-dimensional structures (high orientation and high specific surface area) and controllable morphologies (hollow, porous, and core-shell), which are highly desirable in many applications, including composites, electromagnetic interference (EMI) shielding, lithium-ion batteries, supercapacitors, microwave absorption, sensors, and fuel cells. In practical applications, there are three common methods for preparing CNFs, namely chemical vapor deposition (CVD), template method, and spinning. Although the CVD method can provide uniform and pure CNFs, the disadvantage of this method is that it is difficult to obtain long fibers and large-scale CNFs at a low cost. Spinning methods for converting polymer precursors into nanofibers include wet spinning, melt spinning, and electrospinning. The main advantage of spinning methods is that they can produce large quantities of nanofibers, both in the laboratory and on an industrial scale. Among them, electrospinning uses electrostatic forces and is widely used to produce uniform, flexible, continuous, low-cost, and scalable nanofibers.

The main point of this paper

Importance of electrospinning technology:

Electrospinning is a common and effective technology that can directly prepare CNFs. The regular diameter and ideal morphology of CNFs are highly dependent on electrospinning parameters such as feed rate, voltage, collector distance, solution conductivity and viscosity, medium humidity, etc.

Precursor materials for CNFs:

Precursors of more than 200 carbon skeleton polymers have been used to prepare electrospinning-based CNFs. Polyacrylonitrile (PAN) and polyethylene oxide (PEO) are two commonly used polymers with good carbon yield and mechanical properties.

Morphological design of CNFs:

By adding a variety of modifications to the basic process of electrospinning, different carbon nanofiber morphologies can be designed, such as random structure, arranged structure, twisted structure, cross-linked structure and hybrid structure.

Coaxial electrospinning technology:

Coaxial electrospinning is considered to be a promising alternative technology to overcome the inability of traditional electrospinning methods to spin low-conductive polymers and non-polymer materials (such as metal oxides, ceramics, semiconductors, etc.).

Electrical properties of CNFs:

The electrical conductivity of CNFs is related to factors such as carbonization temperature, different nano-dopants, and morphological parameters. With increasing carbonization temperature, ordered domains of graphite structure evolve, thereby enhancing the conductivity of CNFs.

Effect of nano-dopants:

Naturally conductive nanomaterials such as carbon nanotubes (CNTs), graphene, and metal oxide components are introduced into CNF precursors to improve their electrical properties.

Preparation of copper-coated core-shell carbon nanofibers by coaxial electrospinning: Effect of pressure on their structure and conductivity

Attention to electrospun CNFs:

Electrospun CNFs have gained great attention due to their unique properties, but the limitation of conductivity restricts their application

Application of coaxial electrospinning method:

In this paper, copper-coated core-shell CNFs were prepared by coaxial electrospinning method and heat-treated to study the effect of different loads on the surface structure and electrical properties of electrospun nanofiber felt

Parameter optimization and characterization:

The morphology and structure of compressed CNFs were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The surface conductivity of CNFs was measured using four-point probe technique

Effect of pressure on the structure and conductivity of CNFs:

The results show that the pressure applied to the nanofibers slightly deforms the graphite-like framework and increases the defect structure of CNFs. The increase in these defects is accompanied by an increase in the quaternary nitrogen (QN) content in CNFs, indicating that QN may exist in the graphite-like lattice

Significant improvement in electrical conductivity:

These effects become more pronounced with increasing pressure on the nanofibers. With increasing loading, the electrical conductivity of CNFs increases significantly, reaching around 100.7 Scm−1 at 5 tons

Summarize

Core-shell carbon nanofibers were prepared by coaxial electrospinning, with a core liquid of copper acetate-PEO composite and a shell liquid of polyacrylonitrile solution. The effects of different pressures on the electrical and structural properties of the electrospun nanofiber mats were investigated. After carbonization at 1000°C, the nanofibers showed a hollow morphology with diameters between 500 and 600 nm. XRD data showed that the intensity of the copper oxide peak decreased with increasing pressure values, which was associated with the decrease in the interfiber spacing. XPS and Raman spectroscopy results showed that the graphitic domains of the CNF mats decreased slightly with increasing pressure, while the quaternary nitrogen concentration increased relatively. This finding supports the view that quaternary nitrogen atoms may be integrated into the graphitic lattice of the carbon nanofibers. The conductivity of the carbon nanofiber mats increased significantly with increasing loading, reaching a conductivity of about 1007 μ m−1 at 5 tons. This enhancement in conductivity can be explained by the increased concentration of defects in the graphitic lattice and the transfer of additional electrons to the delocalized π system when the quaternary nitrogen is incorporated into the graphite-like structure.