Metallo-Corroles Supported on Carbon Nanostructures as Oxygen Reduction Electrocatalysts in Neutral Media

In this work, we report the investigation of Fe and Co triphenylcorrole complexes supported on two different carbon supports as eletrocatalysts for the ORR in neutral pH media, comparing their performances with the corresponding tetra- phenylporphyrin complexes. Cyclic voltammetry experiments were acquired in neutral phosphate buffer demonstrating that corroles exhibit a superior catalytic activity towards ORR than porphyrins, as demonstrated by more positive oxygen reduc- tion peak potential (Epr) and half-wave potential (E1/2) values of corroles. Also, iron complexes performed better than cobalt ones, showing an ORR activity even superior to that of platinum taken as reference, as demonstrated by RDE experiments. We investigated the role of the axial ligand on the ORR activity of the macrocycles, and we found that Epr and E1/2 values are more positive along the series: PPh3Co < py2Co = μ-oxoFe2 < FeCl. By contrast, there was not much difference in activity support- ing the porphyrinoids on carbon nanotubes or carbon black pearls, indicating that the effect of carbon support is less im- portant to that of the axial ligand. The results allowed pointing at iron corroles as a promising class of molecular catalysts for application as cathodes in biolectrochemical systems at neutral pH, such as microbial fuel cells.