Activated carbons from agricultural waste solvothermally doped with sulphur as electrodes for supercapacitors

Abstract

Revalorization of an agricultural waste from olive oil industry was performed by transforming it into activated carbon. In such a way, a material with excellent textural properties (high surface area and large micro and mesopore volumes) was obtained by carbonization and chemical activation of solid residues from olive oil industry. Moreover, this activated carbon was solvothermally treated in order to improve its electrochemical properties by adding sulphur and oxygen functionalities on its surface. The treatment was able to introduce a great proportion of sulphur and oxygen, mainly located on the external surface of sample. This modification led to functionalized materials with not only larger capacitance (325 versus 158 F g−1 at 0.125 A g−1 in H2SO4 1 M), but also with a greater retention at higher current densities (large capacitance even at current densities as high as 30 A g−1), due to their lower electrical resistance. Furthermore, the amount of electric energy stored by these materials was largely increased (from 21.8 to 37.0 Wh kg−1 in H2SO4 1 M) as well as their power density (from 7393 to 34360 W kg−1 in H2SO4 1 M). Several charge/discharge cycles were performed in order to test the cyclability of these materials, showing not significant reduction on their electrochemical properties after 12,500 cycles.