Lignin-based carbon fiber: A renewable and low-cost substitute towards featured fiber-shaped pseudocapacitor electrodes

Lignin-based carbon fiber (LCF) is originally developed to substitute PAN-based CF for structural applications. Nevertheless, the intrinsic heterogeneous structure of lignin renders the derived LCF with relatively inferior mechanical properties. The mechanical properties as well as other features (sustainable precursor, small diameter, good scalability, low-cost, high flexibility, etc.), however, is promising for functional applications such as fiber-shaped electrodes. In this work, LCF was produced from 100% lignin via melt-spinning, stabilization, and carbonization. The LCF shows high tensile strength of 401 MPa with superior flexibility. To develop the fabrication strategy of LCF-based pseudocapacitors, the mechanism of polyaniline (PANI) electrochemically depositing on LCF was investigated. It was found low CV scan rate (10 mV s−1) was necessary to allow the well-distributed deposition of PANI on LCF. Electrochemical tests prove that LCF-PANI can be used as a low-cost but high-performance electrode, which delivered high areal specific capacitance of 136.26 mF cm−2 at 0.19 mA cm−2. Upon assembling, the device can be bended and twisted (real-time) at arbitrary angles without sacrificing its capacitance. This work is the first attempt to apply LCF towards the fiber-shaped pseudocapacitor electrodes and will define further opportunities for LCF valorization.