Kinetic study of oxygen reduction reaction on tantalum oxide-based electrocatalysts produced from oxy-tantalum phthalocyanines in acidic media

• Published in: Electrochimica acta 2015-11, Vol.182, p.789-794
• Main Authors: Uehara, N., Ishihara, A., Nagai, T., Matsumoto, M., Imai, H., Kohno, Y., Matsuzawa, K., Mitsushima, S., Ota, K.
• Format: Article
• Language: English
• Subjects: non-platinum cathode; oxygen reduction reaction; oxygen vacancy; polymer electrolyte fuel cell; tantalum oxide
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2015.09.161

In our previous study, we prepared tantalum oxide-based cathodes from oxy-tantalum phthalocyanines by heat treatment under low oxygen partial pressure for polymer electrolyte fuel cells. We revealed that the high onset potential for oxygen reduction reaction (ORR) indicated a low hydrogen peroxide formation rate due to the large extent of crystalline distortion of orthorhombic Ta2O5. However, the hydrogen peroxide formation rate was consistent with an apparent four-electron reaction rate because it included the effect of the hydrogen peroxide reduction reaction. Therefore, in this study, we calculated the individual rate constants of the ORR for tantalum oxide-based cathodes to obtain the four-electron reaction rate (four-electron reduction rate of O2/two-electron reduction rate of O2) and investigated the factors influencing the four-electron reaction rate. The values of the four-electron reaction rate for the tantalum oxide-based cathodes were larger than 1, indicating that the four-electron reaction mainly occurred on the oxide surface. A higher four-electron reaction rate was obtained in the case of severe crystalline distortion and shrinkage of orthorhombic Ta2O5 due to the large number of oxygen vacancies.