ORGANOSULFUR CONDUCTING POLYMER COMPOSITE CATHODES - I - VOLTAMMETRICSTUDY OF THE POLYMERIZATION AND DEPOLYMERIZATION OF 2,5-DIMERCAPTO-1,3,4-THIADIOZOLE IN ACETONITRILE/

This paper describes general trends in the redox potential and solubil ity of a dimercaptan, 2,5,-dimercapto-1,3,4-thiadiazole (DMcT), and it s various derivatives in acetonitrile, and illustrates how these trend s manifest in the cyclic voltammetry observed at glassy carbon electro des. Attention is focused on the polymerization/depolymerization proce sses which are the origins of the excellent charge-storage capabilitie s of electrodes based on the DMcT family of compounds. The extent of o ligomerization/polymerization of DMcT at glassy carbon is shown to inc rease with increasing overpotential and/or oxidation time, as judged f rom its subsequently observed quasi-stable depolymerization wave. Oxid ation of dimer DMcT results in extensive precipitation onto the electr ode, relative to that observed for oxidation of monomer DMcT, as expec ted in light of solubilities observed for those compounds in acetonitr ile. The protonation state of the compounds is shown to have a conside rable effect on both their solubility and, as reported previously in p art, redox potential. Similarly, chemical coupling of the redox proces ses of these compounds to their protonation state and, for DMcT, to a disproportionation reaction known to occur for its oxidation product(s ) complicates analysis of the system as a whole. However, from conside ration of all of the observed trends, a general picture emerges illust rating the redox character of DMcT during polymerization and depolymer ization. Most importantly, it is shown that the electrochemical irreve rsibility typical of those processes can be avoided by careful control of the protonation state and solubility of the electroactive species, allowing the measurement of quasi-reversible redox couples. That and other results are discussed in the context of the use of DMcT in secon dary battery electrodes.