The general behaviour of potentiostatically grown gold oxide films during the oxidation of phenol in basic solutions has been studied using cyclic voltammetry. No catalytic activity is observed and phenol oxidation is prevented when the oxide film consists of both α-and β-oxides. The depletion of β-oxide is accompanied by rapid electrode passivation, showing that the presence of Au(OH) 3 is essential for the oxidation process to take place. A tentative reaction mechanism based on the IHOAM model of electrocatalysis is proposed to account for the participation of the redox mediator couple Au(I)/Au(III).In solutions having high concentrations of KClO 4 or KCl and short reaction times chlorination occurs at gold oxide electrode films, without polymerization at temperatures lower than 308 K and 321 K respectively. Oxidation and chlorination reactions occur with apparent activation energies of ca 17 and 70 kJ mol -1 respectively : this indicates that oxidation is favoured at lower concentrations of the additives.Aqueous wastes containing phenolic contaminants are resistant toward purification and toxic toward microorganisms in conventional biological treatment reactions. As a 'front-end' technology aimed at their detoxification rather than complete mineralization, electrolysis can be used ahead of biological treatment (1). In general, phenols cause deactivation of the anode, reportedly via formation of polyoxyphenylene (POP) deposited when phenoxy radicals attack unreacted substrate. Deactivation by the polymer occurs more slowly at oxide-based electrodes (2, 3) and their activity varies greatly with the nature of the oxide (4). Although gold is the noblest and most inert of metals, and is a very weak chemisorber, it displays a very wide range of electrocatalytic activity especially in base (5). Electrocatalytic processes have been widely studied, firstly to understand their reaction mechanism better and secondly to improve their relevance to industrial applications. The reaction mechanisms can be studied by modifying the structure of the electrode surface in order to influence the adsorption of the different species involved in the electrocatalytic processes. One way of modifying the catalytic surface is the oxidation of the metal by potentiostatic or potentiodynamic polarization. Potentiostatic pretreatment of a polycrystalline gold (pc-Au) electrode at high overpotentials results in thick film growth consisting of ␣-and -oxides (6, 7). The objective of this study was to increase our knowledge of the mechanism of phenol oxidation at potentiostatically grown gold oxide films in alkaline solutions of various compositions and especially to examine the effect of additives on the thickness and catalytic properties of the oxide.