Lignin-derived heteroatom-doped hierarchically porous carbon for high-performance supercapacitors: “Structure-function” relationships between lignin heterogeneity and carbon materials

Abstract

Sustainably sourced lignin is a desired precursor for carbon materials due to its cross-clinked aromatic structure and high carbon content. However, the heterogeneity of lignin feedstock presents non-negligible effects on its physicochemical properties and thereby substantially influences its applications in carbon materials fabrication. In this work, fractionation of corn stalk enzymatic hydrolysis lignin via a simple two-step ordinal dissolution was adapted to reduce lignin heterogeneity and further improve the microstructure and electrochemical performances of lignin-derived heteroatom-doped carbon materials. The results revealed that the fractionation process successfully obtained three lignin fractions with sequentially increasing molecular weight and specific surface area. When the three lignin fractions were subjected to carbonization/activation to fabricate N/P/S co-doped carbon, the F3-derived carbon material (LC-F3) showed the highest specific surface area (2022.4 m2/g) and the best heteroatom doping effect due to the improved activation process resulted from the largest specific surface area of F3. Moreover, the good thermal stability of F3 also contributed to the maintenance of disordered structure during carbonization. Therefore, LC-F3 exhibited excellent specific capacitance (337.2 F/g, 0.5 A/g) and cycling stability (96.5% after 10,000 cycles) as a consequence of its high disordered level, heteroatom doping density and specific surface area. Consequently, this work systematically evaluates the effects of lignin fractionation on the physicochemical structural and electrochemical performances of the carbon materials and further proposes a simple strategy to enhance electrochemical properties of the heteroatom-doped carbon materials through lignin fractionation.