We studied the oxygen reduction reaction on a typical carbon supported Pt fuel cell catalyst in the presence of different anions. Similarly to smooth polycrystalline and single crystal Pt electrodes, the oxygen reduction reaction (orr) activity decreases in the order ClO4- > HSO4- > Cl-, consistent with the increasing adsorption bond strength of the anions. The orr properties of Pt/Vulcan in the presence of adsorbed Cl can be interpreted as a superposition of the individual orr properties of the Pt(111)-Cl-ad and Pt(100)-Cl-ad solid / liquid interface, both with respect to kinetic limitations and to the formation of H2O2. This is in qualitative agreement with the assumed cubo-octahedral Pt particle shape. Although these results were obtained in liquid electrolyte, similar reduced activity and enhanced formation of H2O2 can be expected in a PEMFC, therefore indicating the necessity of chloride free electrode preparation schemes in order to avoid performance losses and/or corrosion/degradation effects.