Heat-treated iron(III) tetramethoxyphenyl porphyrin chloride supported on high-area carbon as an electrocatalyst for oxygen reduction - Part II. Kinetics of oxygen reduction

Oxygen reduction was investigated at FeTMPP-Cl adsorbed on the Black Pearls carbon and heat-treated at temperatures from 200 to 1000 degrees C. Kineti c parameters of the reaction and the dependence of the reaction rate on the heat-treatment temperature were established in acid and alkaline media. It was found that the O-2 reduction rate increases with increase in the heat- treatment temperature of the electrocatalyst, reaching a plateau at 700 les s than or equal to T less than or equal to 1000 degrees C. The reaction rat e was higher in alkaline solution on all electrocatalysts examined, but its dependence on the heat-treatment temperature was the same as in acid media . Like similar other macrocycle catalysts, FeTMPP-Cl/BP was found to be met hanol-tolerant. The effect of sulfate, perchlorate, and phosphate anions wa s also investigated and no influence on the reaction rate was found. Activi ties of FeTMPP-Cl/BP and Pt/BP electrocatalysts were compared. FeTMPP-Cl/BP heat-treated at 700 less than or equal to T less than or equal to 1000 deg rees C showed similar activity to Pt/BP if they are compared in alkaline so lution, but in acid solution, the reaction rate on the Pt electrocatalyst w as higher. The controversy in the literature on the role of metallic Fe par ticles in O-2 reduction catalysis is discussed. Comparison of present resul ts with previous cyclic voltammetry and TEM investigations of the same elec trocatalyst gave further evidence that some other products of the heat-trea tment are responsible for the high activity of the catalyst. (C) 1999 Elsev ier Science S.A. All rights reserved.