SPring-8, the large synchrotron radiation facility

A research group led by Yasumasa Takagi (assistant professor) and Toshihiko Yokoyama (professor) of the Institute for Molecular Science, in collaboration with a research group led by Yasuhiro Iwasawa (professor) of the Innovation Research Center for Fuel Cells, the University of Electro-Communications, and a research group led by Mizuki Tada (professor) of the Research Center for Materials Science, Nagoya University, and Tomoya Uruga (research scientist) of JASRI, developed an ambient-pressure photoelectron spectroscopy instrument that is used with hard X-rays^*1 produced at SPring-8.^*2 They successfully achieved in situ hard X-ray photoelectron spectroscopy of catalytic electrodes during the operation of a polymer electrolyte fuel cell for the first time in the world.

Although fuel cells have been put to practical use as a next-generation energy source and progressively applied to automobiles, many issues remain to be solved, such as the improvement of power generation performance and the reduction in the usage of expensive platinum catalysts in the cathode. Understanding the electronic states of platinum in electrodes during the operation of a fuel cell is crucial to addressing these issues; however, the electronic states of platinum are difficult to investigate and have been studied with limited methods. Photoelectron spectroscopy^*3 is a method of measuring the energy of photoelectrons emitted from a sample irradiated with X-rays and is very effective for investigating the electronic states of materials. However, it has been difficult to observe electrodes during the operation of a fuel cell in which reaction gas exists because the sample needs to be maintained in high vacuum in conventional photoelectron spectroscopy.

The researchers of this study developed an ambient-pressure hard X-ray photoelectron spectroscopy instrument that enables photoelectron spectroscopy under an ambient pressure of 3,000 Pa. They installed the instrument at the beamline constructed by the University of Electro-Communications under a New Energy and Industrial Technology Development Organization (NEDO) program, BL36XU (Catalytic Reaction Dynamics for Fuel Cells), at SPring-8. They also developed a new polymer-fuel-cell-type measurement cell that operates as a fuel cell in this instrument and succeeded in the hard X-ray photoelectron spectroscopy of electrode catalysts during the operation of a fuel cell for the first time in the world. The changes in the electronic states of platinum nanoparticles in electrodes that depend on the voltage applied between the electrodes of the fuel cell were observed. This means that the investigation of the electronic states in electrodes during the operation of a fuel cell, which was difficult by conventional methods, has now become possible. This instrument will enable the observation of various fuel cell electrodes during operation in the future, promoting the development of fuel cell electrodes and catalyst materials.

This research was conducted under the theme of “Study of Reactions in Catalytic Structures Using Time- and Spatially Resolved X-ray Absorption Fine Structure (XAFS) Techniques” as a part of the NEDO project “Development of Technologies to Promote Application of Polymer Electrolyte Fuel Cells / Development of Basic Technologies / Analysis of Structure, Reaction and Mass Transfer in Membrane Electrode Assembly (MEA) Materials.” Their achievements were published online in Applied Physics Letters, an applied physics journal published by the American Institute of Physics, on 1 October 2014. (DOI No.: 10,1063/1,4897007)

Publication:
Applied Physics Letters
Title: "In situ study of an oxidation reaction on a Pt/C electrode by ambient pressure hard X-ray photoelectron spectroscopy"
Authors: Yasumasa Takagi, Heng Wang, Yohei Uemura, Eiji Ikenaga, Oki Sekizawa, Tomoya Uruga, Haruhiko Ohashi, Yasunori Senba, Hirokatsu Yumoto, Hiroshi Yamazaki, Shunji Goto, Mizuki Tada, Yasuhiro Iwasawa and Toshihiko Yokoyama.
doi: 10.1063/1.4897007