Tantalum oxide-based electrocatalysts made from oxy-tantalum phthalocyanines as non-platinum cathodes for polymer electrolyte fuel cells

The development of non-platinum-based cathodes is required in order to commercialize polymer electrolyte fuel cells. We have previously investigated group 4 and 5 transition metal oxides because they exhibit high chemical stability under cathode conditions and are less costly than platinum. In this paper, tantalum oxide-based cathodes were prepared from oxy-tantalum phthalocyanines by heat treatment under low oxygen partial pressures. We successfully obtained nano-sized tantalum oxide-based particles dispersed on multi-walled carbon nanotubes to increase the oxygen reduction reaction (ORR) current density. We investigated the factors which influence ORR activity in terms of the onset potential and ORR current density. The onset potential increased with increasing crystalline distortion of orthorhombic Ta2O5, which was experimentally observed as changes in the position and full width at half maximum of the Ta2O5 (0 0 1) peak in the X-ray diffraction patterns. In addition, the amount of the deposited carbon strongly influenced the ORR current density because it affected the surface area of the oxides and the formation of local electron conduction paths.