Incorporation of Pyridinium Axial Ligands for Fe Phthalocyanines Anchorage on Carbon Nanotubes Electrodes for Biomimetic Oxygen Reduction

Metallo phthalocyanines confined on electrode surfaces such as graphite and carbon materials have been used extensively as active molecular catalysts for a variety of reactions1. When anchored on carbon nanotubes the activity of these catalysts increases by almost 2 orders of magnitude in part due to an increase in effective area. Recently, Cao et al. have shown that anchoring FePc to carbon nanutubes using an axial ligand produces very active materiales for the reduction of O2 in alkaline media, mimicking in this fashion the function of cytochrome c in the catalytic reduction of O2 in living systems. In this work we have used iron phthalocyanines (FePcs) for O2 reduction in basic medium incorporated single wall carbon nanotubes (SWCNTs) modified with pyridiniums axial ligands (py) obtained by reacting diazonium salts. The two phthalocyanines used correspond to the unsubstituted iron phthalocyanine FePc and perchlorinated iron phthalocyanine (16(Cl)FePc)). Our results show that for ORR: (i) As expected, carbon nanotubes produce a pronounced increase in electrode surface area, favoring the incorporation of more active sites of the molecular catalysts studied. (ii) The incorporation of the axial ligand causes an increase in the rate of ORR, resulting in the onset for ORR to more positive values compared to the response of electrodes having FePcs without the axial ligand.. (iii) Of the studied phthalocyanines, 16(Cl)FePc exhibits the highest catalytic activity (Fig.1) due to the synergistic effect of Cl electron withdrawing substituents and the electron withdrawing pyridinium axial ligand. Acknowledgment: Fondecyt Nº 1140192 and postdoctoral proyect Nº 3150271. 1. Zagal, J. H., Griveau, S., Silva, J. F., Nyokong, T. & Bedioui, F. Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions. Coord. Chem. Rev. 254,2755–2791 (2010). 2. Cao, R. et al. Promotion of oxygen reduction by a bio-inspired tethered iron phthalocyanine carbon nanotube-based catalyst. Nat. Commun. 4, 2076 (2013). Figure 1