Lowering of Polythiophene Polymerization Activation Energy on Its Electrodeposition from Protonated Thiophene Monomer in a Binary Solvent
Duke Orata *
Department of Chemistry, University of Nairobi, P.O. Box-30197-00100, Nairobi, Kenya.
Eric Okong’o
Department of Chemistry, Jomo Kenyatta University of Agriculture and Technology, P.O. Box-62000, Nairobi, Kenya.
Daniel Ichangi
Department of Geology, University of Nairobi, P.O. Box-30197-00100, Nairobi, Kenya.
*Author to whom correspondence should be addressed.
Abstract
In this paper we report on poly-thiophene electrodeposited from thiophene monomer initially protonated in concentrated sulfuric acid prior to mixing the resultant product in a binary solvent mixture consisting of varying ratios (vol/vol) of acetonitrile and water.
Cyclic voltammetry was used in the electrochemical profiling of the redox processes in the resultant mixture. The cyclic voltammograms obtained for all the binary solvent mixtures studied were reversible with significantly improved oxidation -reduction peaks, signifying improvement in the faradaic processes associated with polythiophene electrodeposition.
The relative non-dependence of the polythiophene redox processes on the protonation –deprotonation equilibria in the 1:1 acetonitrile –water binary system is a strong pointer to the key role of polaron /bipolaron model for polymerization in polythiophene.
The cyclic voltammograms obtained in the various binary solutions mixtures for acetonitrile-water mixtures were reproducible. They had well –behaved electrochemistry and are quasi-reversible
Analysis of oxidative peak current and scan rates for the various binary solvent mixtures, yielded linear plots for peak current versus square root of scan rate, suggesting diffusion limited processes.
Graphical plot of anodic versus cathodic peak currents demonstrated that for every incremental increase in anodic peak current there was a corresponding increase in the cathodic peak current pointing to a highly efficient redox process.
In this paper the significant improvement in the electro-deposition of the poly-thiophene is attributed to lowering of the polymerization activation energy associated with the formation of polarons/bipolarons which are key in the polymerization of thiophene monomeric units. The functional dependence of pH is captured in the resultant expressions.
Keywords: Polythiophene, thiophene monomer, polymerization, voltammograms, binary solvent