The kinetics of oxygen reduction at a gold electrode was studied in 0.5 M sulfuric acid, in which different kinds of straight-chain [CF 3 (CF 2 ) 2 CH 2 OH, CF 3 CF 2 CH 2 OH, and CF 3 CH 2 OH] and branched [(CF 3 ) 2 CHOH] fluorinated alcohols were added. The adsorbed layers of the fluorinated alcohols were used as models of the fluorocarbon phase of the perfluorinated polymer electrolyte in gas-diffusion electrodes in proton-exchange membrane fuel cells. A rotating ring-disk electrode was used to determine kinetic parameters for O 2 reduction and to detect intermediate H 2 O 2 formation. The kinetics of oxygen reduction were strongly dependent on the molecular structure of fluorinated additives. The addition of the straight-chain fluorinated alcohols enhanced the kinetic current density while addition of the branched alcohol did not. The linear C 3 fluorinated alcohol, CF 3 CF 2 CH 2 OH, gave the maximum enhancement effect. Oxygen is reduced predominantly via the two-electron series path in the range of 0.4 to 0.0 V at Au, on which no effect of fluorinated additives was observed. The rate constant for intermediate H 2 O 2 reduction, k 3 , was negligible in the range 0.40-0.25 V, whereas it increased with decreasing E D in the range 0.25-0.0 V. In the lower potential range, k 3 decreased with an increase in the concentration of fluorinated alcohol and this decreasing tendency was greatly dependent on the molecular structure of the fluorinated alcohol.