A model has been proposed according to which the voltammetric charge involved in the Ti/IrO2 electrodes is due to two contributions: a faradaic contribution due to surface redox activities at the IrO2 coating and a non-faradaic contribution due to the charging of electrical double layer (q(dl)*). The later q(dl)* has been proposed as a tool for the estimation of the relative surface area of the Ti/IrO2 electrodes. Differential electrochemical mass spectrometry (DEMS) measurements using (H2O)-O-18 has demonstrated that we are dealing with an active electrode in which the surface redox couple IrO3/IrO2 acts as mediator in the oxidation of formic acid (FA). From the voltammetric measurements using different IrO2 loading and FA concentrations, the kinetic parameters of FA oxidation via the surface redox couple IrO3/IrO2 have been determined. Finally a model has been proposed considering that FA oxidation at Ti/IrO2 anodes is controlled by mass transfer. The good agreement between the experimental results and the model indicates that the surface reaction between FA and the electrogenerated IrO3 is a fast reaction. (C) 2008 Elsevier Ltd. All rights reserved.