Synthesis and electrochemical properties of potassium 5-trifluoromethyl-1,3,4-thiadiazole-2-thiolate/disulfide redox couple

A new redox couple, composed of the reduced species potassium 5-trifluoromethyl-1,3,4-thiadiazole-2-thiolate 2 and the oxidized species 5,5′-bis (2-trifluoromethyl-1,3,4-thidiazole) disulfide 3, was synthesized and characterized chemically and electrochemically when dissolved in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMITFSI). Platinum (Pt), glassy carbon (GC) and cobalt sulfide-coated indium tin oxide glass (ITO-CoS) electrodes were used. The diffusion-controlled redox processes were shown to be electrochemically irreversible. At higher electrolyte temperature, the current densities are enhanced, and the potential difference between the anodic and cathodic peaks is decreased, in conjunction with a decrease in the viscosity of the electrolytic medium. The best electrocatalytic performance was obtained with the ITO-CoS electrode, followed by GC and Pt electrodes. A greater thiolate/disulfide ratio favors larger anodic current densities, whereas a smaller ratio leads to higher cathodic current densities. Preliminary stability studies of the ITO-CoS electrode confirmed the very good electrochemical and mechanical stability of this electrode considered as a serious candidate to replace platinum as the counter electrode in dye-sensitized solar cells (DSSCs). The electrolytic media studied in this work exhibits a very low absorption of visible light, contrarily to the conventional I3−/I− mediator, offering the possibility of illumination of the device via the counter electrode.