Photon Factory Activity Report 2022 #40 (2023)

BL-12C, NW-10A/2021G564

In-situ PTRF-XAFS study on ultrathin layer Pt on Au(111)
Kaiyue DONG1, Daiki KIDO1, , Chenghao YANG1, Bing HU1, Soichi TOMIDOKORO1, Takahiro
WADA2, Satoru TAKAKUSAGI1, and Kiyotaka ASAKURA1*
1
Institute for Catalysis, Hokkaido University, Kita 21-10, Sapporo, Hokkaido, 001-0021, Japan
2
Tokyo Medical and Dental University, Yushima 1-5-45, Bunkyo-ku, Tokyo 113-8510, Japan
1 Introduction
Platinum has been proved to possess an outstanding
catalytic property in fuel cell technology, especially in
Oxygen Reduction Reaction (ORR) occurring at thecathode of the fuel cell system. However, the high priceof Pt has greatly limited the wide spreading of PEMFCs.
Some reports have revealed that the core-shell (Pt@M)
structure not only increases the utilization of Pt even up
to 100%, but also enhances the specific activity [1]. In
Pt@Au core-shell nanocluster, shorter Pt-Pt distanceswere found[2] though the Pt-Pt distance was suggested tobe elongated and to have the same as Au-Au on Pt onAu(111) single crystal surface in our previous studies.[3]But the Pt on Au(111) system was the mixture of Pt
monolayer and [PtCl2]n structures so that the Pt-Pt
distance was not so clearly determined in the previouswork. In order to confirm the Pt-Pt distances were reallylonger on Au(111) surface we prepared flat sub
monolayer Pt on Au(111) and we carried out in-situ
electrochemical polarization dependent total reflection
fluorescence X-ray absorption fine structure spectroscopy(in-situ EC-PTRF-XAFS) for model catalyst system ofPt/Au(111) with a well-defined surface.[4]2 Experiment
Before Pt deposition experiment, Au(111) wasannealed by butane gas to reveal the characteristic surface.
A sub monolayer (subML) Pt species was deposited by aso-called Cu underpotential deposition (Cu UPD) andSurface Limited Redox Replacement (SLRR)[3]. The
freshly prepared PtsubML/Au(111) sample was set on ahomemade electrochemical (EC) cell with 0.1 M HClO4
filled. All above-mentioned operation was carried out in aN2-filled glovebox. The in-situ EC-PTRF-XAFS of Pt L3edge was measured at BL12C using a Si(111) double
crystal monochromator. Total reflection condition wasadjusted by a 5-axis goniometer. The fluorescence signal
was detected by a 7 channel SDD. Due to the interference
coming from the Au L3 edge, the measurement had tostop at k = 7 Ǻ-1.

Fig.1 (Left) In-situ EC-PTRF-XAFS apparatus.
(Right) details of in-situ EC cell.
3 Results and Discussion

Figure 2 shows Pt L3 edge XANES spectra at reduced
condition (+0.4 V vs RHE) which had a slightly higher
white line (WL) compared to that of Pt foil. Pt 4f XPS
suggested the main species was metallic species as shownin Fig.3. To determine the Pt-Pt bond distance, theconstrained thorough search analysis(CTS) was carriedout for both s- and p-polarization [5-7] using the model
structure of monolayer Pt on Au (111) as shown in Fig.4.
Figure 5 shows the CTS results and experimental data.
The Pt-Pt bond distance was confirmed to be 2.88 Å.
This is due to the epitaxial growth of Pt monolayer on Au.

Fig.2 Pt L3 edge XANES spectra.

Fig.4 Pt19/Au(111) model.
Acknowledgement

Fig.3 XPS for subML
Pt/Au(111) sample.

Fig.5 thorough-search result ins-pol.

This work was supported by JSPS Grant-in-Aids for
Scientific Research 20H00367.
References[1] Oezaslan et al., J. Phys. Chem. Lett. 4. 3273(2013).
[2] B.Hu et al., J.Phys.Chem.C 126, 1006-1016 (2022).
[3] Q. Yuan et al. J. Phys. Chem. C. 122, 16664 (2018).
[4] S. Takakusagi et al., Top. Catal. 56, 1 (2013).
[5] D. Kido et al. Acc. Mater.Surf. Res., 5, 148(2020).
[6] D.Kido et al. e-J Surf.Sci.Nanotech. 18, 249(2020).
[7] D.Kido et al. Chem.Lett., 51, 538(2022).
* askr@cat.hokudai.ac.jp