Experimental Elucidation of the Role of Cocatalyst for High Efficiency in Fuel Cell Reactions

Guidelines for Simultaneously Realizing Reduced Use of Platinum and High Efficiency in Fuel Cells

2012.05.29
(2012.07.05 Update)

National Institute for Materials Science
Japan Atomic Energy Agency

The NIMS Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN) and other NIMS units, in joint research with the Japan Atomic Energy Agency (JAEA), clarified for the first time the role of a metal oxide type co-catalyst in high efficiency in reactions involving the electrodes of polymer electrolyte fuel cells (PEFC) by in-situ measurements using synchrotron radiation.

Abstract

  1. A group of Dr. Takuya Masuda, a NIMS Special Researcher,  Dr. Toshiyuki Mori, Group Leader, and Dr. Kohei Uosaki, Field Coordinator, of the Batteries and Fuel Cells Field of the Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN) of the National Institute for Materials Science (President: Sukekatsu Ushioda),  in joint work with the NIMS MANA/Synchrotron X-ray Station at SPring-8 and Dr. Daiju Matsumura, Researcher, Dr. Kazuhisa Tamura, Researcher, and Dr. Yasuo Nishihata, Chief Researcher of the Quantum Beam Science Directorate of the Japan Atomic Energy Agency (JAEA; President: Atsuyuki Suzuki), clarified for the first time the role of a metal oxide type cocatalyst in promoting high efficiency in reactions involving the electrodes of polymer electrolyte fuel cells by in situ measurements using synchrotron radiation.
  2. Polymer electrolyte fuel cells (PEFC) are power generating devices which make it possible to extract electric power with high efficiency using the reverse reaction of the electrolysis reaction of water. In particular, hydrogen-oxygen fuel cells using hydrogen fuel have numerous advantages, namely, (1) operation at a comparatively low temperature (<100°C), (2) easy realization of compact size, and (3) clean device which discharges only water. As a result, high expectations are placed on commercialization of this technology as a power source for electric vehicles and mobile electronic devices and in household cogeneration systems. At present, platinum, which is a scarce material, is used as the electrode material of both electrodes, and its oxygen reduction reaction activity is low, necessitating use of a large amount of this element. This has been a serious problem for practical application of PEFC.
  3. Recently, a team headed by Dr. Mori developed a platinum-cerium oxide nano-hybrid in which cerium oxide is added as a cocatalyst, and showed that this hybrid displays high oxygen reduction reaction activity in comparison with the conventional platinum catalyst. In the present research, the role of the co-catalyst cerium oxide in increasing reaction activity was clarified by applying an in situ measurement technique for solid-liquid interfaces using X-rays generated by the large-scale synchrotron radiation facility SPring-8, with the aim of developing high performance electrode materials.
  4. As a result, it was found that the oxygen reduction reaction with the conventional platinum catalyst proceeds in a state of partial oxidation of the platinum surface, and the intrinsically high reaction activity of platinum is lost when the surface is in this oxidized state. On the other hand, with the newly-developed platinum-cerium oxide nano-hybrid, partial charge exchange occurs at the interface where the platinum and cerium oxide are in contact, and the cerium oxide is oxidized sacrificially in place of the platinum. As this suppresses oxidation of the platinum, the hybrid catalyst demonstrates the high catalytic activity of platinum itself.
  5. Because this research proved the importance of the platinum/cerium oxide interface in the reduction reaction of oxygen, as described above, it is expected to contribute not only to reduction of platinum consumption by formation of higher efficiency interfaces, but also to development of fuel cell electrode materials with higher activity.
  6. These research results were published in the American scientific journal, “Journal of Physical Chemistry C.”