Electrode kinetics of oxygen reduction on platinum in trifluoromethanesulphonic acid

Abstract

The kinetics of oxygen reduction at Pt in trifluoromethanesulphonic acid (TFMSA) (0.05–6.0 M) and in 1.0 M TFMSA with addition of small concentrations of phosphoric acid (0.003–0.1 M) was investigated using the rrde technique. In TFMSA, the oxygen reduction current on the oxide-covered Pt was found to be smaller than that on the oxide-free Pt surface. This result is consistent with the greater amonut of hydrogen peroxide produced on the oxide-covered Pt. A reaction order of one-half with respect to the oxygen concentration for the oxygen reduction reaction was obtained from the ring-disc data. Addition of increasing amounts of phosphoric acid to TFMSA resulted in a progressive decrease in the oxygen reduction current and in an increase of the reaction order with respect to oxygen. On the basis of these experimental results the reaction mechanism proposed for the oxygen reduction of Pt in TFMSA is the fast dissociative adsorption of oxygen, followed by the slow electron transfer step.