Comparison of the electrochemical properties of activated carbon prepared from woody biomass with different lignin content

In this study, activated carbon was prepared from lignocellulosic biomass and its electrochemical properties were analyzed and compared. The highest total specific net energy efficiency was 1.12 kW/kg when the mixed softwood (MSW) was ground, while the value was as low as 0.54 kW/kg for logging residue (LOR). The lignin content ranged from 27.38 to 33.43% depending on the biomass type, and the value was the highest for LOR. The activated carbon was prepared by carbonization and activation with KOH. A partially graphitic structure was observed in the MSW by high-resolution transmission electron microscope, X-ray diffractometer, and X-ray photoelectron spectroscopy analyses. The activated carbon prepared from MSW and mixed hardwood showed higher specific surface areas (> 1832 m²/g) and micropore volume (> 0.69 cm³/g) than commercial activated carbon (1729 m²/g and 0.64 cm³/g). The gravimetric specific capacitance (17.1 F/cc) and the specific capacitance retention ratio of cycling stability (91.1%) properties were excellent in MSW. However, lignin content was not proportional to the improvement in electrochemical properties.