Preparation of activated carbon nanofibers using degradative solvent extraction products obtained from low-rank coal and their utilization in supercapacitors

Abstract

In this study, low-rank coal was separated into three solid fractions by a degradative solvent extraction method. The high-molecular-weight extract (termed Deposit) had some outstanding properties such as high carbon content, almost no ash, high aromaticity, good thermoplasticity and high solubility in DMF. Therefore, Deposit with some proportion of polyacrylonitrile (PAN) was used to prepare activated carbon nanofibers by electrospinning and CO₂ activation. Moreover, the utilization of these carbon nanofibers as a supercapacitor electrode was preliminarily investigated. The results showed that the specific surface area of the Deposit-based carbon nanofibers (1005 m² g⁻¹) was significantly higher than that of the nanofibers obtained from pure PAN (688 m² g⁻¹). TGA simulations showed that this was caused by the different thermal decomposition behaviors of Deposit and PAN during the stabilization and activation processes. In addition, the Deposit-based carbon nanofibers showed a better specific capacitance (192.6 F g⁻¹ at 1 A g⁻¹) and cycling performance (retention rate of 89.8% after 1000 cycles at 5 A g⁻¹) in a 6 M KOH electrolyte. The factors, such as the enhanced surface area and pore volume and decreased average fiber diameter, affected the electrochemical properties of the carbon nanofibers. Thus, it has been proven that the high-molecular-weight extract obtained from low-rank coal by degradative solvent extraction is a promising precursor for the preparation of carbon nanofibers with unique electrochemical properties.