Photon Factory Activity Report 2019 #37 (2020)

BL-9A, BL-12C/2017G156

An in-situ PTRF-XAFS Investigation into Self-terminated Pt Deposition on Au(111)
Qiuyi YUAN1, Yuki WAKISAKA1, Satoru TAKAKUSAGI1, Yohei UEMURA2, Takahiro WADA3
and Kiyotaka ASAKURA1*
1
Institute for Catalysis, Hokkaido University, Kita 21 Nishi 10, Sapporo, Hokkaido, 001-0021, Japan
2
Institute for Molecular Science, Okazaki, Aichi 444-0867, Japan
3
Tokyo Medical and Dental University, Tokyo 113-8510, Japan

2 Experiment
2D Pt layer was deposited on the Au(111) surfacefollowing the H-terminated deposition protocol [5]. A -0.7
V vs Ag/AgCl potential was applied on a Φ15mm Au(111)single crystal electrode in 0.5 M NaCl + 3 mM H2PtCl4 for
5 s with RPM of 400, then transferred into the in-situ
PTRF-XAFS cell which was described previously [7] for
XAFS measurements. Experiment was conducted at BL9A
and BL12C, PF. We use a 19-element Ge MSSD(Canberra) as fluorescence detector. A Zn filter (𝜇𝑡=3) wasused to remove the elastic scattering from the electrolyte.
3 Results and Discussion
At 0.45 V, where there was no adsorptions of H nor
OH on the Pt surface, s- and p-polarization EXAFS
spectra were shown by black curves in Fig.1b, c). The
oscillation basically followed that of Pt metal, indicatingthat the Pt deposit on the Au surface mainly existed in theform of Pt metal. Based on the EXAFS spectra, weproposed a 2D Pt layer on Au(111) with the thickness of 2
atomic layer height, as shown in Fig. 1a), with blue atoms

indicating Pt and yellow ones of Au. The resulted EXAFS
simulation were shown by red curves in Fig.1 b, c). Thisstructure were also consistent with STM results.
a)b)

0.05

0.45 V sFEFF

0.04
0.03c(k)

0.02
0.01
0.00

-0.01
-0.02
-0.03

R = 0.326

-0.04
3c)

4

5

6k (Å-1)

7

0.04

8

90.45 V pFEFF

0.03
0.02
0.01c(k)1 Introduction
It has been proved that core-shell catalyst could be oneof the feasible directions in polymer electrolyte fuel cell(PEFC) designs [1]. Many efforts have been made todevelop catalysts with uniform core-shell structure withnoble metal like Pt as shell, to improve the stability as wellas activity [2]. Displacement methods were used for a longtime as surface decoration method using noble metals [3].
However, it was later found that the Pt shell was not
perfectly formed, as multi-layer islands were formed on thecore material instead of a homogeneous shell [4]. This
would further cause problems including the core material
out-leaching and the stability decrease.
In our study, we deposited Pt on Au using selfterminating deposition method [5], which could result in amore uniform 2D Pt coverage on the Au surface. To furtherunderstand the catalyst activity of this monolayer Pt
covered Au surface, it is necessary to first understand its
structure, like Pt-Pt and Pt-Au bond length, and electronic
structure change under in-situ condition using model
structure like single crystal to exclude other complicating
factors like the inhomogeneity of the substrate. Here weused in-situ polarization dependent total reflection
fluorescence (PTRF) XAFS, which can provide the three
dimensional(3D) structures of metals highly dispersed on
the flat surfaces.

0.00

-0.01
-0.02
-0.03

R = 0.479-0.043456k (Å-1)

789Fig. 1: a) proposed model structure. b) EXAFS oscillationof Pt/Au(111) at 0.45 V, s-polarization. c) EXAFS
oscillation of Pt/Au(111) at 0.45 V, p-polarization.
References[1] S. Alayoglu, A.U. Nilekar, M. Mavrikakis and B.
Eichhorn, Nature Materials 7, 333 (2008)[2] M. Oezaslan, F Hasche and P. Strasser, J. Phys. Chem.
Lett. 4, 3273 (2013)[3] R.R. Adzic et al., J. Am. Chem., Soc. 131, 17298 (2009)[4] M. Shao et al., Chem., Rev., 116, 3594 (2016)[5] Liu, Y., et al, Science 338, 1327 (2012)[6] Q. Yuan., et al., J. Phys. Chem. C 122, 16664 (2018)* askr@cat.hokudai.ac.jp