Oxygen reduction (OR) is a critical reaction occurring at one of the electrodes of both fuel cells and metal-air batteries. However, this reaction has slow electrode kinetics and thus, the catalysis of this reaction has vital importance. The studies in literature showed that some phthalocyanine (Pc) complexes had the ability of displaying high catalytic performance for dioxygen reduction, due to their highly conjugated π-electrons systems and rich redox properties.¹ There is a strong relationship between the redox properties of Pc compounds and their efficiency as OR catalyst. Thus, the determination of the electron transfer properties of novel Pc derivatives is highly important.

This work involves the identification of redox properties of various novel mononuclear tetra-2,6-dimethoxy-substituted cobalt(II), iron(II), manganese(II) and nickel(II) Pcs by voltammetry and electrocolorimetry supported in situ spectroelectrochemistry in nonaqueous solution medium. It also includes determination of their suitability for usage as OR catalyst in energy conversion and/or storage devices such as fuel cells and metal-air batteries. In situspectroelectrochemical measurements provided critical support for the complete assignment of the redox processes, i.e., whether the reactions are metal- or ligand-based. The complexes displayed enriched reversible or quasi-reversible ligand and/or central metal-based one-electron redox processes. The electrocatalytic performances of the novel Pc complexes with different metal centers towards OR have been tested and compared by dynamic rotating disk and rotating ring-disk voltammetry measurements of the MPc/C(Vulcan XC-72)/Nafion modified glassy carbon electrodes in aqueous medium. In general, the complexes display different catalytic performances depending on the differences in the interactions of their metal centers with oxygen.

References

[1].  İ. Koç, M. Özer, A.R. Özkaya, Ö. Bekaroğlu, Dalton Trans., 32, 6368–6376 (2009).

Acknowledgement: This work was supported by Marmara University, Scientific Research Projects Committee (Project No: FEN-C-YLP-080715-0345).

Fig.1. Molecular structure of mononuclear tetra-beta substituted metal Pc template.