The effects of lignin structure on the multiscale properties and electrochemical performance of activated carbons

Lignin is a nature’s wonder most abundant aromatic biopolymer and a promising precursor for a wide range of sustainable carbon materials (CMs). However, the effects of lignin structural heterogeneity on the properties and performance of lignin-based CMs are still poorly understood. In this paper, we address the influence of the lignin structural heterogeneity on the properties of lignin-based activated carbons (ACs). Taking two structurally different kraft (KL) and hydrolysis (HL) lignins, we show that they result into ACs with different properties and electrochemical performance in supercapacitor application. In similar carbonization and activation conditions, ACs from HL showed higher specific capacitances than ACs from KL. The difference between the two groups of ACs could not be solely attributed to the difference in their specific surface areas. They were rather found to result from different particle morphologies, pore size distributions, pore wall nanostructures, and surface chemistries, as revealed by multivariate data analyses. Moreover, we observed that KL and HL had different thermophysical behaviors and reactivities during the thermal treatment, which would have influenced the porosity development and surface oxygenation levels and consequently the electrochemical performance of the derived ACs. This work also shows that it is possible to engineer ACs from HL with electrochemical performance close to the commercial YP-50F Kuraray AC, which implies that less pure, carbohydrate-containing lignins are no less advantaged compared to purer KL to produce high-performance ACs for supercapacitor application.