The initial stages of oxidation of aqueous solutions of p-chlorophenol (pcp) and p-nitrophenol (pnp) on Bi-doped PbO2 electrodes have been studied. From deconvolution and analysis of UV-Vis spectra of the solutions obtained during electrochemical oxidation, benzoquinone and aliphatic acids were identified as the primary oxidation intermediates; oxidation of benzoquitlone was found to be the slow step during the early stages of the electrochemical combustion process. The effect of competing adsorption of pep and pnp on Bi-PbO2 was also examined, and the presence of pnp in solution was found to inhibit the rate of oxidation of pcp during concurrent oxidation of both phenols. (C) 2003 Elsevier Ltd. All rights reserved.