Factors Affecting ORR Activity of Nb-Added TiOx Catalyst Using Carbon Support for PEFC

Cup-stacked carbon nanotubes (CSCNTs) were covered with niobium-added titanium oxide by hydrolysis method to increase effective surface area of the oxides. In addition, reductive heat-treatment was performed to produce the active sites for the oxygen reduction reaction (ORR). The use of CSCNTs as supports was found to be effective to form the electron conductive path. The ORR currents of the Nb-added titanium oxide supported by CSCNTs significantly larger than those of Nb-added titanium oxide powder mixed with Ketjenblack. On the other hand, the ORR current at 0.6 V had maximum at the heat-treatment temperature of 800°C. We focused on the ratio of Ti3+ of the catalysts and found that the positive correlation between the ratio of Ti3+ and the ORR current density at 0.6 V. Therefore, it was found that the formation of the oxygen vacancies on the oxide surface strongly affected the ORR activity.