The oxidative degradation of phenolic compounds (4-chlorophenol and 4-nitrophenol) was studied using different electrochemical systems involving ozone formation at PbO2 anodes: (i) direct electrolysis at constant current; (ii) ex-situ use of O-3 and (iii) combined use of anodically generated stream of O-3/O-2 fed into the cathode where H2O2 is electrogenerated by O-2 reduction. We show that the latter advanced oxidation method gives the best results: it is a Fenton-type degradation of the target pollutants taking place in the cathodic compartment by reason of the highly oxidizing environment brought about by radicals that are formed mainly in the reactions of O-3 with OH- and HO2-. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3589913] All rights reserved.