Enzymatic hydrolysis lignin derived hierarchical porous carbon for supercapacitors in ionic liquids with high power and energy densities

Abstract

Porous carbons were obtained by chemical activation of hydrochar, prepared by hydrothermal carbonization using enzymatic hydrolysis lignin originated from the butanol fermentation of corn straw. The intermediate hydrochar was activated using different KOH/hydrochar weight ratios to evaluate the influence of these ratios on its electrochemical properties. The materials thus prepared exhibited high specific surface areas in the range 1290–1660 m² g⁻¹ mainly attributed to the three-dimensional hierarchical texture made up of abundant micropores, small mesopores and macropores, and high electrical conductivity in the 4.0–5.4 S cm⁻¹ range. Consequently, the samples show high specific capacitance, superior rate performance and outstanding durability in three-electrode and two-electrode systems in 6 M KOH. The as-assembled symmetric supercapacitor in an ionic liquid electrolyte system exhibits a superior energy density of 46.8 W h kg⁻¹ and a value of 22.9 W h kg⁻¹ is maintained even at an ultrahigh power density of 25 400 W kg⁻¹. These materials possessing excellent structural features are an ideal candidate for high performance supercapacitors.