The influence of Nafion(R) film on ORR kinetics and H2O2 formation on a Pt electrode was investigated using RRDE in 0 1 M HClO4 It was found that the Nafion(R)-coated Pt system showed lower apparent ORR activity and more H2O2 production than the bar e Pt electrode system From the temperature sensitivity it was revealed that the apparent activation energies of ORR in the Nafion(R)-coated Pt system were lower than the bare Pt electrode system and the H2O2 formation was suppressed with the increase of the temperature In order to analyze the results furthermore other systems (0 1/1 0 M HClO4/CF3SO3H) with the bare Pt electrodes were also examined as references It was exhibited that the ORR kinetic current the H2O2 formation and the apparent activation energies of 1 0 M CF3SO3H system were close to those of the Nafion(R)-coated Pt system We concluded that the orientation of anion species of Nafion(R) and CF3SO3H to the Pt surface via water molecules as well as a fluorocarbon polymer network of Nafion(R) might block O-2 adsorption resulting in the smaller effective surface area of the Pt electrode for ORR the smaller ORR kinetic current and the more H2O2 production (C) 2010 Elsevier Ltd All rights reserved