Abstract
Electrocatalytic activities of metal-phthalocyanines (Me-Pc) and -dibenzotetraazaannulenes (Me-TAA) for oxygen reduction have been measured by standardized dispersion electrode in 4.5-n. H2SO4 . The most active chelates are Fe-Pc and Co-TAA. Normally substitution of the ringsystem leads to a strong decrease in activity. Exceptions are - COOH, - NO2 with Me-Pc, -Cl with Me-TAA. In alcaline media, the Co-chelates are especially active. Electrocatalytic activity and catalase effect are not correlated. A mechanism is given, which is called “redox-catalysis”. In a chemical step, the electrocatalyst is oxydized by the oxygen to the cation, which is reduced in an electrochemical follow up step. This gives a satisfactory explanation for the complementarity of activity and stability of these electrocatalysts.
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