In this work we investigate the acetaldehyde electrooxidation reaction on PtRh electrodeposits as a function of their composition. Potentiodynamic results show that the balance between CO2 and acetic acid pathways depends on the PtRh composition. By using in situ FTIR we interpret this dependence in terms of a dual role played by Rh during acetaldehyde electrooxidation. Rh seems to favor the break of C-C bonds (favoring the production of CO2) whilst prevents the deliverance of oxygen-containing species, thus inhibiting the oxidation steps. (C) 2010 Elsevier Ltd. All rights reserved.