On previous papers it was shown that composite electrodes, incorporating Y zeolite, in its sodium form, were able to induce the electro-oxidation of phenol; it was also established that exchanging sodium by protons seriously deteriorated the electrode's ability to oxidise phenol, indicating that cation composition of the zeolite was very important in the electrode's performance. In this work the influence of the nature and content of cations in the zeolite and in the supporting electrolyte were studied for this electro-oxidation. Cations such as lithium, sodium, potassium, calcium and praseodymium were used. The presence of these cations, as compensating cations in the zeolite, bears a direct influence the electrode's performance, but the cation content of the electrolyte also has a bearing on this performance. Although ion exchange processes probably occur during measurements, it was not significant in comparison with the phenol diffusion into the electrode. The influence of having different cations in the electrolyte, such as sodium, potassium, cesium or ammonium (NH4+) was also inspected and it was observed that they also have a bearing on the electro-oxidation of phenol, probably due to their influence in the mass transfer of phenol into the composite zeolite/graphite electrode and probably to molecular traffic effects originated in the ion-exchange processes that occur simultaneously with the electro-oxidation, in which the last one has less influence. Among all conditions and zeolites that were tested, the electrode using a sodium Y zeolite with a SUM ratio of 2.5, composited with graphite, in the combination with a sodium phosphate buffer, gave the best results for the electro-oxidation of phenol. (c) 2007 Elsevier B.V. All rights reserved.