Elucidation of the Redox Behavior of 2,5-Dimercapto-1,3,4-thiadiazole (DMcT) at Poly(3,4-ethylenedioxythiophene) (PEDOT)-Modified Electrodes and Application of the DMcT−PEDOT Composite Cathodes to Lithium/Lithium Ion Batteries

Abstract

The redox reactions of DMcT at PEDOT-modified glassy carbon electrodes (GCEs) in acetonitrile (AN) have been investigated via cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM) in order to elucidate the redox reaction mechanism. A redox couple at -0.29 V versus Ag/Ag+ was assigned to the dimerization process of singly protonated DMcT (DMcT-1H), and a second couple observed at +0.42 V was assigned to the polymerization process of the protonated DMcT dimer. Our investigations revealed further that the anodic current response at +0.55 V (polymerization process) has a shoulder at +0.38 V ascribed to the dimerization process of doubly protonated DMcT (DMcT-2H), indicating that the redox couple at +0.42 V is the overlapping response of the polymerization of the protonated DMcT dimer and the dimerization of the DMcT-2H monomer. It was also confirmed that the dimerization process of DMcT-1H at -0.29 V proceeded not only at the surface of a PEDOT film but also inside the film as previously suggested. Moreover, the thermodynamics of these redox reactions at PEDOT-modified GCEs are dependent on the basicity (or acidity) of the solution, as anticipated and previously shown at unmodified GCEs. The oxidation of DMcT occurs at less positive potentials and the reduction occurs at more negative potentials in the presence of base. On the basis of the results obtained, the full redox reaction scheme for DMcT at a PEDOT-modified GCE is proposed.

Poly[dithio-2,5-(1,3,4-thiadiazole)] (PDMcT)–poly(3,4-ethylenedioxythiophene) (PEDOT) composite cathode for high-energy lithium/lithium-ion rechargeable batteries

“…Additionally, organic materials offer the advantage of making them relatively low cost and derived from abundant resources, being particularly suitable to applications requiring large amounts of electroactive materials, such as power sources for pure electric vehicles (PEVs) and hybrid electric vehicles (HEVs). However, the practical application of these compounds has been hindered because of the sluggish kinetics of the redox reactions at room temperature [3,17,18], the lack of electronic conductivity, and the poor charge/discharge durability in liquid electrolyte systems [19].…”

“…We have studied organosulfur-based composite systems in which a conducting polymer (e.g., PEDOT) is employed as an efficient electrocatalyst to accelerate the redox reactions of organosulfur compounds such as 2,5-dimercapto-1,3,4-thiadiazole (DMcT) [9,19]. An additional advantage of conducting polymers is that they possess their own redox reactions, and thus can also be used as an electroactive material in their own right [20].…”

Electrochemical Energy Generation and Storage. Fuel Cells and Lithium-Ion Batteries

“…42,46,47 Additional advantages of conducting polymers are that they possess their own redox reactions (and thus additional capacity) and exhibit electronic conductivity when they are oxidized (p-type doping) or reduced (n-type doping). 48 Therefore, they can also be used both as an electroactive material and for providing electronically conductive pathways in their own right.…”

“…46 It was revealed that, while the thermodynamics of the redox reactions of DMcT are strongly dependent upon the basicity or acidity of the solution employed, all forms of DMcT (Scheme 1) are electrocatalyzed at PEDOT film-coated GCEs. For an anodic potential scan, DMcT-2H and singly protonated DMcT (DMcT-1H) are oxidized to the protonated dimer at +0.38 and À0:26 V vs. Ag/Ag þ , respectively, and doubly deprotonated DMcT (DMcT 2À ) is oxidized to the deprotonated dimer at À0:30 V. The dimerization of DMcT-1H occurs not only at the surface of a PEDOT film but also inside the film.…”

“…54 The proposed anodic and cathodic reactions are summarized in Schemes 2 and 3, respectively. 46 The potentials reported are the peak potentials for the reactions and referenced against a Ag/Ag þ electrode. Furthermore, we have quantitatively analyzed the electronexchange reaction between DMcT and PEDOT via rotatingdisk electrode (RDE) voltammetry.…”