Research on Redox Properties of Novel Electronically Conducting Materials and Their Application

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The subject of this research project is to develop electroactive materials with novel or improved functionality by molecularly coupling organosulfur compounds and conducting polymers. The promise of these composite materials was examined in the application to a cathode material for lithium secondary batteries with high energy density.1.Synthesis and Electropolymerization of Organosulfur-Functionalized Pyrrole MonomersOrganosulfur functional groups such as thiols and disulfides were covalently introduced to a pyrrole monomer in an attempt to enhance electrocatalytic activity of conducting polymers toward organosulfur redox reactions. Pyrrole monomer, to which disulfide group was attached, was successfully synthesized and further electropolymerized at electrode surfaces. A polypyrrole derivative thus obtained showed higher electroactivity compared to that of unmodified, pristine polypyrrole prepared under the same condition, which suggested that the redox reaction of the disulfide group … More was activated due to electrocatalysis of polypyrrole chain. However, clear evidences for the redox transformation between disulfide and thiol have not so far obtained from Raman spectroscopy and electrochemical quartz crystal microbalance. Further characterization of the polymer is currently under way.2.Electrocatalytic Redox Reactions of Organosulfur Compounds on Poly(3,4-ethylenedioxythiophene) (PEDOT)In this study, high electrocatalytic activity of poly(3,4-ethylenedioxythiophene) (PEDOT) toward organosulfur redox reactions was confirmed for the first time. It was observed that redox reactions of an organosulfur compound such as 2,5-dimercapto-1,3,4-thiadiazole (DMcT) was efficiently activated at a PEDOT-modified carbon electrodes. PEDOT also electrocatalyzed the redox reactions of DMcT dimer and oligomers. Such acceleration of the DMcT redox reactions, which is essential to practical application of organosulfur compounds to batteries, was ascribed to electronic properties of PEDOT matrix, into which DMcT was incorporated. Chronopotentiometric results indicated that the redox reactions of DMcT were enough fast at PEDOT modified electrodes to sustain an electrolysis current even at 1.0 mA/cm^2 and coulombic efficiency for DMcT was virtually 100%. Less