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 usi ng a rotating ring-disk electrode. In order to detect H2O2 quantitatively, a method based on cyclization of the ring electrode potential had to be app lied. The number of electrons exchanged per O-2 molecule was estimated to b e between 3.45 and 4, depending on the electrode potential, but with no sig nificant influence of the heat-treatment temperature. It was possible to ox idize and reduce H2O2 electrochemically. The oxidation reaction was found t o be faster than the reduction. Based on the data reported here, it is post ulated 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 decomposi tion. The influence of H2O2 on the decay in the activity of the catalyst he at-treated at low temperature was discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.