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In this work we have re-interpreted volcano correlations for the oxidation of hydrazine catalyzed by CoMN4 catalysts and found that the highest catalytic activity is observed when the formal potential of the catalyst matches the reversible potential of the reaction, i.e. the hydrazine/dinitrogen reversible potential, that is −0.4959 V vs. SCE at pH 13. This clearly shows that the formal potential of the catalysts needs to be "tuned" or to be very close to the reversible potential of the target molecule to undergo an ET process. This is also true for other reactions we are studying.Electrocatalysis is present in many processes of technological relevance. These electron transfer (ET) reactions involve molecules that for reacting at desired rates, apart from an overpotential, they require the interaction of reactants, intermediates or products with active sites on the electrode surface. 1-3 It is very important to understand the fundamentals of electrocatalysis in order to design better catalytic electrode materials. 1-4 In particular, MN4 macrocyclic complexes like phthalocyanines and porphyrins, when adsorbed on electrode surfaces, catalyze a myriad of electrochemical reactions and in many cases the activity plotted versus the formal potential of the catalyst give volcano correlations. 4 We have shown the importance of "tuning" the formal potential of MN4 macrocyclic complexes for optimizing the electrocatalytic activity of these species for many reactions. 3,4 However in previous work no reference to the reversible potential of the reaction under study has been made. In this work we have re-interpreted data previously published in the literature related to the electrooxidation of hydrazine catalyzed by CoN4 macrocycles adsorbed on graphite electrodes and propose a new mechanism for the reaction. Further, we have found that for Co macrocyclics, in a volcano correlation, the maximum activity is observed for the catalyst that has a formal potential very close or equal to the reversible potential of the hydrazine/dinitrogen couple. This is also true for Fe macrocyclics. 5 This finding is very important since it suggests that to design a catalyst, its formal potential need to be tuned so to approach the reversible potential of the reaction to be catalyzed under the experimental conditions. This seems to be true for other reactions, like the oxidation of L-cysteine catalyzed by CoN4 macrocyclic complexes. 6

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Amino-functionalized multiwalled carbon nanotubes (MWCNT-NH 2 ) were modified with Fe phthalocyanine (FePc) and perchlorinated Fe phthalocyanine (16(Cl)FePc) and deposited on glassy carbon electrodes (GCE). The electrocatalytic activity of these hybrid electrodes was examined for the reduction of molecular oxygen in alkaline media (0.2 M NaOH) using stationary and rotating disk electrodes. Electrodes containing 16(Cl)FePc are more active than those containing FePc. Electrodes containing CNTs are more active than electrodes without CNTs but the higher activity can be attributed to a greater real surface area, compared CGEs and not necessarily to a catalytic effect.

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