http://support.spring8.or.jp/Report_JSR/PDF_JSR_31A/2019A1768.pdf

2019A1768

BL14B2඲཯ᑕ⺯ග XAFS ࡟ࡼࡿⓑ㔠ࣔࢹࣝゐ፹⾲㠃ୖ࡬ࡢ㧗ศᏊࣂ࢖ࣥࢲ࣮ศᏊࡢ྾╔ゎᯒ
Binder Polymers Adsorbed on Surface of Pt Model Catalyst Analyzed byTotal Reflection Fluorescence XAFS࣏ࣥࢳࣕࣀࢵࢡࢳࢼࣃࣥ a, Ώ㎶๛ b, ㇂⏣⫕ c, ᯇᮏ໷ྐ d, ௒஭ⱥே d, ≟㣫₶἞ a
Pondchanok Chinapang a, Takeshi Watanabe b, Hajime Tanida c, Masashi Matsumoto d,
Hideto Imai d, Junji Inukai aaa

ᒣ᲍኱Ꮫ, b JASRI, c JEAE, d ᪥⏘࢔࣮ࢡ

University of Yamanashi, b JASRI, c JEAE, d NISSAN ARC

The structure and the chemical state of a 100-nm Nafion thin film cast on a Pt substrate were examined byin-situ XAFS of Pt. The information of the interfacial properties were combined with the layered structures
obtained by neutron reflectometry.
Key Word㸸 polymer electrolyte fuel cell, binder, Pt model catalyst, total reflection fluorescence XAFS㸯㸬Background and Aim of Research
The structures of polymer electrolyte membranes and catalyst layer binders and the distribution of water
therein are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. To aid
the understanding of the in-plane water distribution, we carried out neutron reflectometry 㻔NR㻕 in J-PARC
on a Nafion® film with a thickness of 150 nm formed on a 20-nm Pt layer deposited on Si㻔100㻕 with a native
SiO2 layer. In this study, ambient pressure X-ray absorption spectroscopy at room temperature in air wascarried out.
㸰㸬Experimental
On an Si㻔100㻕 substrate 㻔2 inch diameter, 1 mm thick㻕 with a native SiO2 layer, Pt was deposited with athickness of approximately 20 nm. An alcohol dispersion of 5 wt% Nafion was spin-coated onto thePt/SiO2/Si㻔100㻕 substrate and annealed at 80 ºC in air for 1 hour. The thickness of the Nafion film wasapproximately 150 nm. X-ray absorption spectroscopy 㻔XAS㻕 in the fluorescence mode was carried out onpristine Nafion/Pt/SiO2/Si㻔100㻕 at the BL14B2 beamline of SPring-8 in air at RT. The glancing angle of theX-rays was set at 0.38 º to realize total reflection, and the fluorescence intensity from the sample wasmonitored at the front of the specimen in the perpendicular direction to the incident X-ray. The XAS
information was obtained from the surface in the depth of approximately 2 nm. As reference samples, a Pt
foil and PtO2 powder were used for conducting XAS measurements in a transmission mode. The extended䠉㻝㻜㻤䠉

X-ray absorption fine structure 㻔EXAFS㻕 data were analyzed by performing standard procedures using theAthena and Artemis programs in the IFEFFIT package. The k2-weighted Ȥ㻔k㻕 data ranging from 0.3 to 2.0
nm were Fourier-transformed into R-space spectra for fitting in Artemis.
㸱㸬ResultsFigure 1㻔a㻕 shows the Pt L3-near-edge regions 㻔Xray absorption near-edge structure, XANES㻕 of pristine
Nafion/Pt/SiO2/Si㻔100㻕 㻔red line, fluorescence mode㻕,Pt foil 㻔black line, transmission mode㻕, and PtO2
powder 㻔green line, transmission mode㻕 obtained in airat RT. As has been reported, the heights of the whitelines of the XANES are directly connected with theoxidation state of Pt. From the XANES, the oxidation
state of Pt in Nafion /Pt/SiO2/Si㻔100㻕 was found to bevery similar to that of a Pt foil. Figure 1㻔b㻕 shows theFourier-transformed EXAFS spectra without a phasecorrection. The peak at ca. 0.27 nm for the Pt foil 㻔blackline㻕 was assigned as Pt-Pt, whereas that at 0.17 nm for
the PtO2 powder 㻔green line㻕 was assigned as Pt-O. In
the spectrum of Pt in Nafion/Pt/SiO2/Si㻔100㻕 㻔red line㻕,no peak was seen for Pt-O. Therefore, the Pt of thepristine Nafion/Pt/SiO2/Si㻔100㻕 was metallic. Theresults have been published elsewhere [1].
Fig. 1㸲㸬Future Plans
In-situ measurements of total reflection fluorescence
XAFS in solution under electrochemical conditions are

Pt L3-edge XANES 㻔a㻕 and Fouriertransformed EXAFS 㻔b㻕 spectra for Pt
foil 㻔black line, transmission mode㻕,PtO2 powder 㻔green line, transmission

now in progress.

mode㻕, and Nafion/Pt/SiO2/Si㻔100㻕㻔red line, fluorescence mode) collected

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[1] "Sublayered Structures of Hydrated Nafion® Thinat room temperature in air.

Film Formed by Casting on Pt Substrate Analyzed
by X-ray Absorption Spectroscopy under Ambient Conditions and Neutron Reflectometry at
Temperature of 80°C and Relative Humidity of 30–80%", T. Kawamoto, M. Aoki, T. Kimura, P.
Chinapang, T. Mizusawa, N. L. Yamada, F. Nemoto, T. Watanabe, H. Tanida, M. Matsumoto, H. Imai,J. Miyaka, K. Miyatake, J. Inukai, (OHFWURFKHPLVWU\, 87, 270 㻔2019㻕.

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