Noel, M. (1984) Studies on electron-transfer and homogeneous redox-catalysis on glassy carbon electrodes. PhD thesis, Madurai-Kamaraj University.

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Abstract

This study examines the structure and redox properties of Glassy Carbon surfaces and their influence on other solution phase electrochemical processes. Cyclic voltammetric technique is employed for surface characterization and evaluation of kinetic parameters of electron transfer and chemical reactions. Even a freshly cleaned Glassy Carbon (GC) surface contains surface functional groups that show redox behavior. In the anodic potential region the surface carbon atoms undergo partial oxidation. In faster sweep cyclic voltammetric experiments these transient carbon-oxygen functional groups are reduced back to carbon skeleton in the reverse sweep. At slow sweep rates the oxidized surface gets stablised which imparts electrocatalytic activity to GC. At extreme cathodic potentials hydrogen adsorption takes place on GC electrode. The voltammetric behavior of GC electrode surface in aqueous sulphuric acid, sodium sulphate, sodium hydroxide and sodium chloride media have been thoroughly investigated. The effect of GC surface structure has a great influence on electron transfer reactions as shown by the study of Ferricyanide/Ferrocyanide redox system. Mild oxidation of GC surface at slow sweep rates and its subsequent reaction to a thin stable oxide layer leads to fast charge-transfer kinetics for this reaction. Based on these studies proper pre-treatment procedures for GC electrodes for various pH regions have been evolved. The supporting electrolyte anions (chloride, sulphate, hydroxide, phosphate oxalate and citrate) either catalyse (chloride) or block and inhibit (oxalate, citrate) the Ferrocyanide/Ferricyanide redox process. Titanous/Titanic redox system forms complexes of varying stability with a number of complexing agents. Among them, the thiocyanate, phosphate, oxalate and citrate complexes show well defined redox properties on GC electrodes. For all these complexes the charge transfer rate however is lower on GC when compared to mercury. As we would be expected the electrode material has no influence on the solution phase redox reactions (reduction of hydroxylamine by titanous ions) associated with electron transfer at the electrode (reduction of titanic to titanous ions). In tri-sodium citrate medium, hydroxylamine is more easily reducible when compared to Titanic citrate and hence the former functions as the redox catalyst and the later functions as a substrate. This probably is the first observation of catalyst-substrate interchangeability depending on pH

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Electron-transfer; Homogeneous redox-catalysis
Subjects:	Electrodics and Electrocatalysis
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	13 Jun 2012 04:57
Last Modified:	13 Jun 2012 04:57
URI:	http://cecri.csircentral.net/id/eprint/2827

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