Structural and Electrochemical Characteristics of Activated Carbon Derived from Lignin-Rich Residue

Abstract

Lignin-rich residue was obtained by sequential acid pretreatment (sulfuric, oxalic, and maleic acid; H-ST, H-OT, and H-MT) and enzymatic hydrolysis (EH). Pretreatment using dicarboxylic acid (oxalic and maleic acid) showed a relatively low solid yield (72.55 and 69.27%) compared with sulfuric acid pretreatment (74.83%). In addition, the enzymatic hydrolysis yield of pretreated biomass differed significantly depending on the acid catalyst used. To investigate structural properties of lignin-rich residue, milled wood lignin (MWL) was extracted. H-MT-EH-MWL and H-OT-EH-MWL were found to have higher M-w and polydispersity values than H-ST-EH-MWL, but the syringyl-to-guaiacyl (S/G) ratio of H-ST-EH-MWL was the highest. The lignin-rich residue was used to prepare activated carbons (ACs) to make commercially viable energy storage materials. These activated carbons showed commercially viable specific surface areas (SSAs) (>2000 m(2)/g) and high rate capabilities (>90% at 50 mA/cm(2)). H-ST-EH-AC had the highest BET SSA value (2182 m(2)/g). H-MT-EH-AC had a slightly lower value (2156 m(2)/g), but H-OT-EH-AC had the lowest value (2079 m(2)/g). The sp(2)/sp(3) ratio of H-ST-EH-AC (3.8) is higher than the others (H-MT-EH-AC: 3.6 and H-OT-EH-AC: 3.1). On the basis of the lignin-rich residue structure, it is considered the high S-type lignin content of H-ST-EH can be attributed to the graphitic structure in H-ST-EH-AC.