Development of Nitrogen-Doped Titanium Oxide Electrocatalysts for PEFCs

Abstract

With their efficiency, high power density, and low/zero emissions, polymer electrolyte fuel cells (PEFCs) are recognized as promising energy converting system. However, high cost and insufficient durability currently hinder their commercialization. Especially, one of the major barriers is the high cost and low stability of platinum (Pt)-based catalysts 1). Thus, developing alternative catalysts with low cost and high stability has been strongly required for the commercialization of PEFCs. In the effort to reduce the cost of PEFCs, we have been developing nitrogen doped titanium oxide (N- TiO2) as a non-noble metal electrocatalyst in NEDO (New Energy and Industrial Technology Development Organization, Japan) project. In this paper, we introduce a new and convenient synthesis method of N-doped TiO2electrocatalysts and their catalytic activities for oxygen reduction reaction (ORR). In this study, we used phthalocyanine (Pc) as nitrogen source in order to dope nitrogen into TiO2. For the high surface area of electrocatalyst, TiO2 nanoparticles were deposited on high surface area carbon supports (C). The carbon supported TiO2 (TiO2/C) and phthalocyanine (Pc) were mixed and heat-treated at 900oC in inert gas atmosphere containing a small amount of hydrogen (H2) and oxygen (O2) in order to finally obtain N-TiO2/C electrocatalysts. TiO2 nanoparticles of ca. 20 nm size deposited on the carbon supports were observed by transmission electron microscope (TEM), indicating that the synthesized N-TiO2/C may have considerably high surface areas. In X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) studies, it was found that the XPS core-level peaks of Ti was very similar to that of Ti-N binding energy and the XRD peak of TiO2 shifted to higher angles, respectively. These results well explain that the nitrogen was successfully doped into TiO2 nanoparticles by our synthesis process. Fig. 1 compares the ORR catalytic activities of the synthesized N-TiO2/C and TiO2/C. The synthesized N-TiO2/C electrocatalyst shows significantly higher ORR catalytic activity than that of TiO2/C. It is believed that the enhanced catalytic activity of N-TiO2/C is due to the doping effect of nitrogen into TiO2. Acknowledgements The authors wish to thank NEDO (New Energy and Industrial Technology Development Organization) for financial support. References Ken-ichiro Ota, Yoshiro Ohgi, Kyung-Don Nam, Koichi Matsuzawa, Shigenori Mitsushima, Akimitsu Ishihara, J. Power. Sources., 196, 5256, ( 2011). Figure 1