Electrospun nanocomposite fibers from lignin and iron oxide as supercapacitor material

Nanofibrous carbon-based electrodes constitute key components in light-weight and environmentally-friendly supercapacitors. However, there is still need to reach higher specific capacitance, better stability of the electrode materials and more efficient energy density. In particular, the carbon electrodes' applications are limited by their low Electric Double-Layer Capacitance (EDLC) and high cost. Our goal is to achieve a supercapacitor electrode with high specific capacitance, combining the fast charging of EDLC and high energy density of pseudocapacitor feature. Here, we report a method to prepare flexible lignin-based composite nanofibers which includes iron oxide nanoparticles (L-CNFs@FexOy nanofibers) in one-step via electrospinning. Morphology, surface chemical compositions, pore structure, phase formation and structure properties of the L-CNFs@FexOy nanofibers were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS), N-2 absorbance, X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction Spectroscopy (XRD) and X-ray Absorption Spectroscopy (XAS). The electrical properties and electrochemical performance of the nanofibers were investigated by using Conductive Atomic Force Microscopy (C-AFM) and Potentiostat/Galvanostat (i.e. CV, GCD, EIS), respectively. L-CNFs@Fe3O4 electrodes exhibit high specific capacitance (216 F g(-1) at 0.1 A g(-1)) and ultra-high energy density (43 Wh kg(-1)). We suggest that the nanostructures developed around the presence of amorphous and crystalline carbon and the iron oxide nanostructure produce the unique porosity and surface area that contribute to the intrinsic electrochemical performance. This model study involving nanostructures formed by earthly-abundant metal compound and biomass carbon presents a new approach to novel, cost-effective and durable electrodes in alternative energy storage application. (C) 2021 The Authors. Published by Elsevier B.V.