| This work studies the chemical and physical structure as well as the mechanism of formation of the passivating film produced on the anode during aqueous phenol electrolysis. Electrode passivation is of interest in the areas of electrochemical waste water treatment, the electrosynthesis of quinones and the production of electropolymerized coatings. The work was carried out in acidic aqueous solutions at a platinum anode and the passivation phenomenon was investigated using infrared and Raman spectroscopy, gel permeation chromatography, chronoamperometry, cyclic voltammetry and X-ray photoelectron spectroscopy. High speed data collection software was developed to carry out the chronoamperometric and cyclic voltammetric work.; Investigation of the electro-polymerization of various substituted phenols showed that for less sterically hindered monomers, polymerization occurred more through direct carbon-carbon coupling of the aromatic rings than through ether linkages. Because of this, the less hindered monomers are able to form completely reacted 1,2,4,6 substituted structures resulting in highly branched and crosslinked products.; The main product of phenol oxidation was oligomers/polymers which typically reach weight average molecular weights around 1000 g/mole after only 30 ms. Chronoamperometry shows that the current decay at the passivated electrode is roughly inversely proportional to time and that the currents at a fixed amount of polymerization reaction follow a Tafel type relationship. These results are interpreted as being due to electron tunneling through a growing insulating film.; Phenol was found to react at both the inner and outer Helmholtz layers (IHL and OHL). Phenol in the IHL is irreversibly adsorbed, conductive and oxidizes with a n{dollar}sb{lcub}rm eff{rcub}{dollar} greater than 18 equivalents/mole. The OHL oxidation is rapid, involving minimal rearrangement of the reactant molecule (n{dollar}sb{lcub}rm eff{rcub}{dollar} around 3 equivalents/mole). Thus, once stable products are formed in the OHL, they must move to the IHL to be further oxidized.; Therefore the initial current flow during phenol oxidation is due mainly to simple, fast OHL reactions. This produces layers of high molecular weight, oxidized material at the electrode surface. The rate determining step is then electron tunneling from reactive molecules, through the immobile oxidized material, to the electrode. As additional layers of oxidized material form, tunneling from the OHL decreases and slower IHL reactions predominate. For elimination of phenols from waste-water, methods of increasing the more thorough IHL reactions are needed. For quinone synthesis the OHL reactions need to be shifted away from coupling type reactions. |
