Oxygen Electroreduction on Zinc and Dilithium Phthalocyanine Modified Multiwalled Carbon Nanotubes in Alkaline Media

Abstract

Dilithium and zinc phthalocyanine derived catalysts supported on multiwalled carbon nanotubes (MWCNTs) have been studied as non-precious metal catalysts for oxygen electroreduction. The electrocatalysts were prepared by simple pyrolysis by varying the pyrolysis temperature and metal phthalocyanine-to-MWCNT ratio. The surface morphology of the catalyst materials was characterized by scanning electron microscopy (SEM) and surface composition by X-ray photoelectron spectroscopy (XPS). The rotating disk electrode (RDE) method was used to determine the electrocatalytic activity of these materials in 0.1 M KOH solution. The oxygen reduction reaction (ORR) activities achieved are comparable to well-studied Fe and Co phthalocyanine based catalysts in alkaline media, showing the great potential of non-redox-active metal phthalocyanine-derived catalysts as cathode materials for metal-air batteries and fuel cells. The number of electrons transferred per O2 molecule was determined by the Koutecky-Levich analysis, which indicated that at high negative potentials the ORR process followed a four-electron pathway. The O2 reduction results obtained in this study show clearly the important role of non-redox-active metal ion in the formation of active sites for ORR on pyrolyzed and carbon supported Li and Zn metallomacrocyclic compounds.