Coal Liquefaction Residues Based Carbon Nanofibers Film Prepared by Electrospinning: An Effective Approach to Coal Waste Management

Abstract

As a major byproduct of direct coal liquefaction, coal liquefaction residue (CLR) waste is environmentally harmful but also valuable. Considering environmental and economic efficiency, exploiting these wastes as electrodes for new generation energy storage devices will increase the economic value and decrease environmental pollution synchronously. In this regard, CLRs are used to prepare carbon nanofibers film for supercapacitors via electrospinning followed by HNO 3 preoxidization, air stabilization, and carbonization processes for the first time. The influences of HNO 3 preoxidization over the formation of fiber morphology, textural structure, surface chemistry, and electrochemical performance are investigated. Our work demonstrates that HNO 3 preoxidization can enhance the content of the heteroatom of the as-spun nanofibers and promote the polymerization of the asphaltene (CLRA) molecular during air stabilization, leading to the changes of the thermal behaviors and thus avoiding the fibers melting successfully. The results show that the obtained sample exhibits a 3D nonwoven network with an average diameter of 200 nm, good flexibility, high content of nitrogen, and large specific surface area. Owing to these merits, the as-obtained sample shows high specific capacitance, excellent rate capability (143 F g −1 at 100 A g −1 ), and long lifespan (98% of its initial capacitance after 10 000 cycles) as supercapacitor electrode.

Flexible All-Solid-State Supercapacitor Fabricated with Nitrogen-Doped Carbon Nanofiber Electrode Material Derived from Polyacrylonitrile Copolymer

“…These values are much higher than the power density of 298.25 W kg –1 and the energy density of 12.03 Wh kg –1 obtained in the sulfuric acid electrolyte. It is also higher than those of other CNF-based aqueous SCPs (Figure G). ,,− …”

Effects of the molecular structure from pitch fractions on the properties of pitch‐based electrospun nanofibers

“…On the other hand, pitch‐based nanofibers are easily fused during electrospinning and stabilization because of too rapid coagulation of pitch‐based nanofibers to spread and more intense exothermic reaction during heat treatment 2,7 . The pitch‐based nanofibers are treated with I 2 and HNO 3 to maintain the morphology of the nanofibers and chemically modify the surface of the synthesized CNFs 8,9 . It is well known that pitch is composed of hundreds of polyaromatic molecules with various chemical structures and molecular sizes, 10 and the difference in molecular structure significantly affect the spinnability of pitch and the structure of the final product 11 .…”

“…Park et al 3,4 reported that the carbon fiber could be obtained from the dimethylformamide (DMF) insoluble and THFS of the pitch, but the thick (>2 μm), discontinuous, and non‐uniformly distributed morphology of fibers emerged. Furthermore, the hexane insoluble‐toluene soluble fraction is used in preparation for CNFs, and the serious bond between the fibers appeared, due to the low softening point of the pitch precursor 8,19 . However, the previous researches usually involve only one pitch fraction to prepare CNFs nothing else the other pitch fractions‐derived nanofibers are compared or investigated.…”

“…2,7 The pitch-based nanofibers are treated with I 2 and HNO 3 to maintain the morphology of the nanofibers and chemically modify the surface of the synthesized CNFs. 8,9 It is well known that pitch is composed of hundreds of polyaromatic molecules with various chemical structures and molecular sizes, 10 and the difference in molecular structure significantly affect the spinnability of pitch and the structure of the final product. 11 However, it is of great difficulty to study a simple molecule of pitch on the influence of carbon materials.…”

“…Furthermore, the hexane insoluble-toluene soluble fraction is used in preparation for CNFs, and the serious bond between the fibers appeared, due to the low softening point of the pitch precursor. 8,19 However, the previous researches usually involve only one pitch fraction to prepare CNFs nothing else the other pitch fractions-derived nanofibers are compared or investigated. Besides, the stabilization and carbonization behavior of nanofibers derived from each pitch fraction is either not discussed.…”