Lignin-derived carbon nanosheets for high-capacitance supercapacitors

Lignin, a type of abundant and low-cost biomass, is successfully utilized as a carbon precursor to prepare carbon nanosheets (CNSs) by freeze-casting of a lignin aqueous dispersion followed by direct carbonization without any activating treatment. The size and specific area of the obtained lignin-derived CNSs can be manipulated by controlling the concentrations of lignin aqueous dispersions, which in turn influences the graphitization degree of the CNSs as confirmed by wide angle X-ray scattering analysis and Raman spectroscopy. X-ray photoelectron spectroscopy study indicates that the CNSs contain similar to 11-16 at% oxygen heteroatoms, which contribute to additional pseudocapacitance. The three-electrode supercapacitors based on optimized CNSs show a high capacitance of 281 F g(-1) at 0.5 A g(-1) current density and good cycling stability in H2SO4 aqueous electrolyte. The study provides a simple, inexpensive, and environmentally friendly method for preparation of CNSs from various water-soluble biomass carbon precursors.