Supercapacitance and oxygen reduction characteristics of sulfur self-doped micro/mesoporous bio-carbon derived from lignin

The growing global concerns about the increased fossil fuel consumption and related environmental issues have motived scientists to find new, green and sustainable energy resources and technologies. In this work, byproduct lignin biomass was successfully converted into sulfur self-doped carbon via in-situ hydrothermal carbonization followed by thermal annealing. The sulfur surface content in the as-prepared porous carbon is up to 3.2 wt % as indicated by the XPS measurements. Beyond the traditional synthesis methods which employ KOH or ZnCl2 treatment to activate the carbon surface, the developed synthesis strategy doesn't include such separate activation step. Activation of the as-prepared porous carbons has been conducted in-situ via a calcium ions during the synthesis process. The resulting materials displayed high BET surface areas up to 660 m(2) g(-1) along with micro/meso porosity and graphitic/amorphous carbon structure. The as-prepared sulfur self-doped electrode materials displayed high electrochemical activity for supercapacitor applications. The sulfur-doped carbon SC-850 electrode exhibited capacitance of 225 F/g at a current density of 0.5 A/g, and high durability where the electrode capacitance did not change over 10,000 cycles at harsh conditions. Additionally, the as-prepared sulfur-doped carbons are promising catalysts for oxygen reduction reaction with 3.4 electrons transferred per molecule at 0.8 V, which approaches the optimum 4-electron pathway.