Electrochemical study of the redox processes of elemental sulfur in organic solvents using poly (3,4-ethylene-dioxy-thiophene) modified glassy carbon electrodes as working electrodes and ionic liquids as electrolytes

Abstract

The commercial use of Lithium-sulfur batteries has been limited by their short service life due to the shuttle effect of polysulfides, which is due to the transport of polysulfides towards the anode and the formation of highly resistive deposits that passivate the electrodes. This problem can be solved by decreasing the transport of these species from the cathode to the anode and simultaneously improving the kinetics of electron transfer reactions. This work studies by electrochemical impedance spectroscopy and cyclic and ac voltammetry the redox reactions of elemental sulfur in either acetonitrile (CH3CN) or dimethyl sulfoxide (DMSO) using as a working electrode either pristine glassy carbon (GC) or GC modified with a thin film of poly-3,4-ethylenedioxythiophene (GC-PEDOT) as working electrodes. Tetrabutylammonium hexafluorophosphate (TBAPF6), 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) and 1-Butyl-3-methylimidazolium triflate ([Bmim][OTf]) were investigated as electrolytes. It was found that the kinetics of the first reduction reaction of S8 on GC is much faster in CH3CN than in DMSO and when [Bmim][OTf] is used as an electrolyte. On the other hand, it was found that PEDOT is electrocatalytic for the first reduction reaction of elemental sulfur. Finally, by encapsulating the sulfur in PEDOT it is possible to increase the retention of the sulfur species inside PEDOT upon redox cycling if pure ionic liquids are used as electrolytes.