Kinetic Studies for the Electrocatalytic Reduction of Bis(2-mercapto-1,3,4-thiadiazoyl)-5,5'-disulfide at a Poly(3,4-ethylenedioxythiophene)Film-Modified Electrode via Rotating-Disk Electrode Voltammetry

摘要

We have carried out a thorough study of the electron exchange reaction between 2,5-dimercapto-1,3,4-thiadiazole(DMcT)and the conducting polymer poly(3,4-ethylenedioxythiophene)(PEDOT),which dramatically accelerates the redox reactions of DMcT at room temperature.A qualitative analysis of the electron exchange reaction was carried out via UV/vis spectroelectrochemistry,while a quantitative study focused on the charge transfer from the reduced form of PEDOT,(PEDOT)_(red),to the DMcT dimer(diDMcT)using rotating-disk electrode(RDE)voltammetry.The kinetic model employed to estimate the charge-transfer rate was based on the analysis previously proposed by Saveant and co-workers(J.Electroanal.Chem.1982,131,1),which takes into account charge propagation in a polymer film on an electrode surface and diffusion of a substrate through the polymer film.Thus,such an analysis is appropriate for the system investigated in this study,in which charge propagation occurs in a PEDOT film via self-exchange and diDMcT is incorporated and partitioned into the PEDOT film.Specifically,we found that the so-called"SR"model,in which the overall process of a system is controlled by the catalytic reaction and the diffusion of a substrate through a film,is the most appropriate one to describe the diDMcT/PEDOT system.This was based on the fact that diDMcT is incorporated and partitioned into the PEDOT film and not directly reduced at the glassy carbon electrode(GCE)surface(at potentials where PEDOT catalyzes the reactions)and that charge propagation through the PEDOT film is sufficiently rapid that the slope of the concentration profile of PEDOT is essentially zero over the film's thickness under the conditions employed in this study.On the basis of such an analysis,the second-order rate constant for the charge-transfer reaction from(PEDOT)_(red)to diDMcT was estimated as 32 M~(-1)s~(-1).This value is significantly larger than that previously obtained for the charge-transfer reaction from the reduced form of polyaniline(PAn)to diDMcT(0.03 M~(-1)s~(-1)),indicating the high electrocatalytic activity of PEDOT toward the redox reactions of DMcT.Moreover,a comparison of the standard rate constants,k~0,for the DMcT/diDMcT redox couple obtained at bare and PEDOT film-modified GCEs indicates that the redox reaction is accelerated by a factor of approximately 12 000 at the PEDOT film-coated GCE.These results demonstrate that the use of conducting polymers,such as PEDOT,as efficient electrocatalysts for the redox reactions of DMcT,is a promising strategy to utilize organosulfur compounds as energy-storage materials in lithium-ion rechargeable batteries.