Iron phthalocyanine correlations

Differences in the orientations and polymorphism have been identified on vapor deposited thick films of iron phthalocyanines supported on glassy carbon (129). These "bulk" differences correlated directly with the ability of the film to catalyze... 

According to the scheme above, the total driving force of the reaction will be given by the applied potential and also by the M(III)/M(II) formal potential of the catalyst, so the catalytic activity could be correlated with the formal potential of the catalyst. Many authors have discussed this issue and it is yet not clear what sort of correlation should be expected. Reduction should occur at the potential of reduction of the M(III)02 adduct and not at the potential of the M(III)/(II) couple. The latter should only be observed if the reaction were outer sphere. For the particular case of iron phthalocyanines and other iron macrocyclics, O2 reduction starts at potentials very close to the Fe(III)/(II) couple ". In contrast, for cobalt macrocyclics reduction of O2 begins at potentials much more negative than those corresponding to the Co(III)/(II) couple . Several authors have reported correlations between activity (measured as potential at constant current) and the M(III)/(II) formal potential and volcano-shaped curves have been obtained -see for... 

Linares C, Geraldo D, Paez M, Zagal JH (2(X)3) Non-linear correlations between formal potential and Hammett parametral of substituted iron phthalocyanines and catalytic activity for the electro-oxidation of hydrazine. J Solid State Electrochem 7 626-631... 

Similarly, using phthalocyanine or porphyrin complexes of a range of transition elements, cobalt and iron again appear to be the best metal ions. Although the mechanisms of the reactions are not fully understood, it is believed that two-electron oxidation is again important and some correlation between oxygen yield and redox potential (M " /M " ) for the phthalocyanine complexes is observed. TTie anomalously low efficiency of zinc compounds compared with those of cobalt, which have similar first oxidation potentials, suggests that the second oxidation potentials are also important. ... 

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