The cathodic reduction of oxygen at metal tetrasulfonato-phthalocyanines: influence of adsorption conditions on electrocatalysis

The mechanism of oxygen reduction at iron tetrasulfonato-phthalocyanine incorporated in polypyrrole

“…We have argued that the "kinetic limitation" as observed for the prewave in basic media is caused by the fact that there are only few dimers present on the surface [3]. The same arguments, applied here, lead to the conclusion that in 0.05 M H,SO,, FeTSPc is almost not present in the dimer form on the graphite surface.…”

“…The basis of this calculation is the assumption [6] that two electrons per molecule are involved in the oxidation of pyrrole to neutral polypyrrole, and that in the oxidized form of polypyrole every four pyrrole units carries one positive charge. As we have shown earlier [3], no adsorption of FeTSPc occurs on Cp under the conditions used for the electrooxidation of pyrrole. This means that for a 1 mC thick layer, 4 X 10-'" mol crnp2 is the total coverage.…”

“…7 display almost no "kinetic li~tation", which means that a 1 mC thick layer contains enough dimer sites to obtain a Levich diffusion behaviour [3]. In Fig.…”

“…For FePc (iron phthalocyanine) adsorbed on graphite, we observed similar behaviour 121. Recently, we proposed a mechanism [3] in which the wave at low overpotential (prewave) is ascribed to dimer species, while the second wave (main wave) is attributed to monomer species. Oxygen reduction has also been investigated at FeTSPc incorporated in polypyrrole, a conducting polymer, by Bull et al 141.…”

Reactivity trends of Fe phthalocyanines confined on graphite electrodes in terms of donor–acceptor intermolecular hardness: Linear versus volcano correlations

“…For explaining the volcano correlations, the so-called Sabatier principle is invoked that essentially states that the most active catalyst in a series of them for a given reaction is the one that binds the key intermediate not too weakly, not too strongly [18]. In previous studies, the relationship between the catalytic activity with structural and thermodynamic parameters of the phthalocyanines has been established [15,[20][21][22][23][24][25][26][27]. These parameters include the formal potential of the M(II)/(I) redox couple in the metal complex [11,21], the role of the substituents in the ligand system [15,20], the magnetic moment [28], and the catalytic activity in other processes [11,[15][16][17][18][19][20][21][28][29][30][31][32][33][34][35][36][37].…”