Effect of fluorinated alcohol on the kinetics of cathodic oxygen reduction at gold electrodes

Abstract

The kinetics of oxygen reduction at Au was studied in 0.5 M H 2SO 4, in which a fluorinated alcohol, 2,2,3,3,3-pentafluoro-1-propanol (CF 3CF 2CH 2OH) was added as a model of the fluorocarbon phase of Nafion® in the electrodes of proton-exchange membrane fuel cells (PEMFCs). A rotating ring-disk electrode technique was used to detect intermediate H 2O 2 formation and to determine kinetic parameters for O 2 reduction. Kinetic parameters such as the kinetic current, Tafel slope, the ratio of the direct four-electron reduction to the series two-electron reduction, and the rate constant for reduction of intermediate H 2O 2 were determined. The kinetic current increased with an increase in the concentration of CF 3CF 2CH 2OH up to 1×10 −2 M, and then decreased with further addition. The rate constant for the reduction of intermediate H 2O 2 decreased monotonously by the addition of CF 3CF 2CH 2OH over the whole concentration range tested. The increase in kinetic current was attributed to a higher concentration of O 2 in the adsorption layer of CF 3CF 2CH 2OH, while the decreases in kinetic current above 1×10 −2 M and in the rate constant were attributed to a decrease in the number of the reaction sites on Au surface.