(625b) Lignin Derived Mesoporous Carbons for Ultracapacitor Electrode Material

Mesoporous carbons were synthesized from pre-crosslinked lignin based materials by surfactant templating with pluronic F127 followed by physical and chemical activation to enhance the pore texture properties. The BET surface areas of the mesoporous carbons were in the range of 185 to 1148 m²/g with total pore volume of 0.28 to 1.0 cm³/g. Besides pore textural properties, these materials were also characterized with electron microscopy, electron energy loss spectra (EELS), small-angle x-ray scattering (SAXS) and x-ray photoelectron spectroscopy (XPS). The ultracapacitor electrodes were fabricated with three samples with varying porosity and aqueous KOH as electrolyte. Majority of the plots in the cyclic voltammetry exhibited rectangular shape exhibiting ideal double layer capacitance. The trend in mass and surface area based specific capacitance did not follow the pore textural properties and that can be attributed to the electrode-electrolyte interactions, surface functionality and various pore geometries. The capacitive characteristics of those materials are investigated with impedance spectra in 10 mHz and 0.2 MHz frequency and a vertical tail in the low frequency domain demonstrated the good capacitive behavior. The electrochemical capacitive characteristics were also investigated with Bode plot, RC characteristics and equivalent electrical circuit by employing the constant phase elements (CPEs).