Since electrochemical power sources that use oxygen as a reactant will be indispensable for society’s future energy needs, there are several projects progressed in global. This study is also one of the research supported by the “Advanced Low Carbon Technology Research and Development Program (ALCA)” of the Japan Science and Technology Agency (JST), and Research Project A of the Venture Business Laboratory of Oita University. The move toward a clean energy society has dramatically spurred interest in battery and fuel cell technology. However, current devices suffer from low energy density or high materials costs, and there is much work to be done to optimize these systems. The promise of oxygen-based electrochemical power systems necessitates the development of components that maximize their potential. Here, we report a fibrous electrode catalyst based on titania oxynitride and activated carbon fibers (TiOxNy-C). This material is produced by liquid phase deposition of TiO2 particles on activated carbon fibers and subsequent ammonia nitridation. Interestingly, we found that this material catalyzes the oxygen reduction reaction (ORR) in both acidic and alkaline electrolyte, which approaches that of the typical Pt catalysts especially in alkaline solution. We also endeavor to discuss the details of its mechanism in the ORR. This catalyst is formed only the highly abundant elements C, O, N, and Ti and therefore, both the costs and material limitations of the electrochemical power sources are expected to be reduced. Optimization and analysis of the active sites, crystallinity, and increment in the surface area will afford significant improvement in the ORR activity. We believe that the findings of this study contribute to the further development of air battery as well as fuel cell for realization a clean energy society.
Taro Kinumoto, Yoshinori Sou, Kohei Ono, Miki Matsuoka, Yasuhiko Arai, Tomoki Tsumura, Masahiro Toyoda. Journal of Power Sources, Volume 273, 2015, Pages 136-141.
Department of Applied Chemistry, Faculty of Engineering, Oita University, 700 Dannoharu, Oita 870-1192, Japan.
A fibrous catalyst of titania oxynitride and carbon is prepared and its catalytic behavior in the oxygen reduction reaction (ORR) are investigated in both HClO4 and KOH aqueous solutions. TiO2 particles are successfully deposited on activated carbon fibers by a liquid phase deposition technique using (NH4)2TiF6and H3BO3. The catalyst obtained after subsequent ammonia nitridation at 1273 K had a fibrous structure with TiOxNy and TiN components.
Interestingly, the product demonstrates catalytic activity for the ORR in not only HClO4 but also KOH aqueous solution. The onset potential in HClO4 solution is assumed to be moderate, at 0.85 V; on the other hand, that in KOH solution is relatively high at 0.95 V. Furthermore, it is considered from the Tafel plot analysis of the KOH solution result that the ORR mechanism follows a peroxide intermediate pathway and the rate-determining step would be a one-electron-transfer reaction to oxygen molecules adsorbed on the active site.