Sustainable supercapacitor electrodes produced by the activation of biomass with sodium thiosulfate

Abstract

High-surface area carbons are produced from biomass-based products (wood sawdust and tannic acid) by means of an environmentally friendly process based on the use of sodium thiosulfate as activating agent and an inert salt (KCl) that serves as a confinement medium for the activation reaction. These porous carbons have high BET surface areas of up to 2650 m2 g-1, large pore volumes of up to 2.3 cm3 g-1 and a porosity that combines micro- and mesopores in different amounts depending on the quantity of activating agent employed. Such carbons have two additional remarkable properties: a) they are S-doped (2–6 wt% S) and b) they have good electrical conductivities in the 2.5–4.5 S cm-1 range. The above properties make these carbon materials highly attractive as supercapacitor electrodes. Indeed, when tested in a variety of electrolytes (H2SO4, TEABF4/AN and EMImTFSI) using commercial-level mass loadings, they show high specific capacitances (up to 200 F g-1, 140 F g-1 and 160 F g-1 in aqueous, organic and ionic liquid electrolytes, respectively) and high capacitance retention at high rates in all the electrolytes in combination with a good stability under cycling and floating modes.