Parallel pathways forming CO2 and acetic acid occur during the electrooxidation of acetaldehyde at Pt in acid medium. The yields of products depend on potential and acetaldehyde concentration. In the whole range of concentrations investigated (2.5 x 10(-3) -0.5 M) and at potentials below 0.6 V, CO2 is the only product of acetaldehyde oxidation. Acetic acid is detected at potentials higher than 0.7 V. According to the analysis of products using FTIR spectroscopy, a maximum yield of CO, production is obtained for an acetaldehyde concentration of 0.01 M at 0.6 V. The pathway forming CO, is strongly inhibited for 0.5 M of acetaldehyde. It is suggested that, at high concentrations, a competition with water for active sites occurs, which inhibits the oxidation of adsorbed species, which probably follow a Langmuir-Hinshelwood mechanism. (c) 2006 Elsevier B.V. All rights reserved.