The performance of sulphur doped activated carbon supercapacitors prepared from waste tea.

The pore structure, high surface area and good conductivity are the key properties for the electrochemical double layer based supercapacitors. The activated carbons were produced from the waste tea, utilising microwave pretreatment with H3PO4 and activation at 450°C. Sodium thiosulfate pentahydrate (Na2S2O3·5H2O) was used as sulphur doping agent at 800°C to enhance conductivity of the activated carbons. Supercapacitor electrodes were prepared from both the activated carbon (WTAC) and sulphur doped activated carbon (WTAC-S) samples and the electrochemical performances were tested in the presence of 6 M KOH and 1 M H2SO4 as electrolytes. The activated carbon samples were characterised by Brunauer-Emmett-Teller (BET) surface area, Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) and Fourier Transform Infrared Spectroscopy (FTIR) analysis techniques. The electrochemical performance analyses were performed by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The specific capacitance values of the WTAC and WTAC-S samples under the 1 A g-1 current density were found to be 89.3, 144.7 F g-1 for KOH electrolyte and 73.8 and 101.9 F g-1 for H2SO4 electrolyte, respectively. The results show that the sulphur doping process enhances the electrochemical performance of activated carbon samples.