Heat-treated iron(III) tetramethoxyphenyl porphyrin chloride supported on high-area carbon as an electrocatalyst for oxygen reduction: Part III. Detection of hydrogen-peroxide during oxygen reduction

Oxygen reduction was investigated on heat-treated FeTMPP-Cl/BP catalysts in 0.1 M H2SO4. The amount of H2O2 generated in the reaction was detected using a rotating ring-disk electrode. In order to detect H2O2 quantitatively, a method based on cyclization of the ring electrode potential had to be applied. The number of electrons exchanged per O-2 molecule was estimated to be between 3.45 and 4, depending on the electrode potential, but with no significant influence of the heat-treatment temperature. It was possible to oxidize and reduce H2O2 electrochemically. The oxidation reaction was found to be faster than the reduction. Based on the data reported here, it is postulated that O-2 reduction on this catalyst comprises both direct and series reaction paths. The increase in the catalyst's activity with the increase in the heat-treatment temperature is more likely caused by the decrease in the activation energy of the reaction than by more efficient H2O2 decomposition. The influence of H2O2 on the decay in the activity of the catalyst heat-treated at low temperature was discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.