Precise identification of such functional groups as well as quantitative evaluation of the relationship between the structure of functional groups and PEFC performance, however, remains unclear. Furthermore, recently developed accessible-carbon supports with inner mesopores requires more advanced analysis methods to identify and separate structures of functional groups outer and inner parts of complex carbon structures. 3-5) In this study, we therefore developed a new approach to identify, and quantitatively analyze functional groups of the carbon supports with spatial distributions by combination of depth resolved x-ray photoelectron spectroscopies and temperature-programmed desorption mass spectroscopy (TPD-Mass).
In order to detect the functional groups existing on the surface and inside the pores of the supports, depth resolved measurements were performed using two types of photoelectron spectroscopy with different X-ray excitation energies. Generally, the photoelectrons emitted from the same orbit have higher kinetic energy, when irradiated with higher energy X-rays. Thus, we can probe electronic structure information of deeper parts of samples with high-energy photoelectron spectroscopy measurements. The functional groups of the whole of supports were detected from hard X-ray photoelectron spectroscopy (HAXPES) using synchrotron radiation with energy of 8 keV (BL16XU and BL46XU at SPring-8), and the functional groups on the surface of supports were detected from the laboratory XPS (Lab XPS) using Al Kα rays with energy of 1.5 keV . By comparing the both, we analyzed the distribution structure of functional groups on the surface and inside the pores of the supports. In addition, identification of functional groups are conducted by TPD-Mass. By analyzing XPS spectra considering TPD-mass results, we quantitatively evaluated functional groups.
As a first step, we demonstrate this approach by using Ketjen Black as a reference sample. The sample was reduced with a pure hydrogen gas for about 30 minutes at room temperature. By using a transfer vessel, it was introduced into the measuring device without air exposure, and the photoelectron spectroscopy measurements were conducted. Figure 1 shows the C1s and O1s spectra measured by HAXPES as an example. The obtained spectra were deconvoluted assuming functional groups identified by TPD-MS. The results of peak fitting was shown in Fig.1 6,7) We can see, in particular, a large amount of quinone, ether, and carbonyl are exist outer and/or innter part of Ketjen Black. When the functional group structure on the surface layer of the carrier was analyzed from Lab XPS data, it was confirmed that the functional group structure was different from that of the entire support. Details will be reported in the presentation. We also report on other carbon supports and the distribution structure of functional groups formed on Pt-based catalysts using them as supports.
Acknowledgement
This work is based on results obtained from a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
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