Optimization of high‐quality carbon fiber production from electrospun aligned lignin fibers

Lignin-based carbon fibers: Insight into structural evolution from lignin pretreatment, fiber forming, to pre-oxidation and carbonization

Lignin remains the second abundant source of renewable carbon with an aromatic structure. However, most of the lignin is burnt directly for power generation, with an effective utilization rate of <2 %, making value addition on lignin an urgent requirement. From this perspective, preparation of lignin-based carbon fibers has been widely studied as an effective way to increase value addition on lignin. However, lignin species are diverse and complex in structure, and the pathway that enables changes in lignin structure during pretreatment, fiber formation, stabilization, and carbonization is still uncertain. In this review, we condense the common structural evolution route from the previous studies, which can serve as a guide towards engineered lignin carbon fibers with high performance properties.

Molecular Modification of Lignin-Based Carbon Materials: Influence of Supramolecular Bonds on the Properties

For the application of lignin-based materials, it is necessary to develop simple and efficient chemical modification strategies for lignin. In this work, the iodization modification strategy is selected to improve the specific surface area and graphitization degree of lignin-based carbon fibers. The introduction of an iodine atom can effectively increase the π electron cloud density of the lignin aromatic hydrocarbon structure. High π electron cloud density can effectively enhance the π-π interaction force between lignin molecules (the supramolecular bonds). The biomass precursors with this intermolecular microstructure exhibit good thermal stability and can maintain the original fibrous morphology during high-temperature treatment, which is beneficial for increasing the specific surface area of biomass-based carbon materials. Furthermore, this intermolecular microstructure also contributes to the graphitization of biomass precursor materials and reduces the spacing of graphite micro-lamellae. The obtained lignin-based carbon fibers with iodization modification exhibit a specific capacitance of 333 F/g at a current density of 1 A/g in the three-electrode tests in 6 M KOH solution. As the assembled supercapacitor, the specific capacitance of lignin-based carbon fibers reaches 87 F/g in 1 M Na₂SO₄ solution. Compared to other modification processes for raw materials, this strategy is simple and efficient and has reference value for the synthesis of other high-performance biomass-based materials.