Photon Factory Activity Report 2016 #34 (2017)

BL-9A, BL-12C/2015G070

XAFS Study of Structure of Pt Monolayer Prepared by Galvanic Displacement
Reaction
Qiuyi Yuan1, Satoru Takakusagi1, Yuki Wakisaka1, Yohei Uemura2, Takahiro Wada3, Hiroko Ariga1
and Kiyotaka Asakura1*
1
ICAT, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo, Hokkaido 001-0021
2
Institute for Molecular Science, Okazaki, Aichi 444-0867, Japan
3
Tokyo Medical and Dental University, Tokyo 113-8549, Japanas shown in Fig.2. Moreover, electrochemicalmeasurement revealed that the surface was a mixture ofPt metal and Pt complex. Electrochemical analysis gave
the percentage of 70 %. The XAFS spectrum could fit
well when a small amount of Pt metal was present with
the PtCl42-. Setting significance level to 0.05, theacceptable lower percentage of complex was 70%. Thus
we concluded that 70% was PtCl42- with 30 % Pt metal.
a)
0.10

χ(k)

0.08

Mixture

0.06

χ(k)

0.04
0.02
0.00
-0.02
-0.04
-0.06
-0.08b)

34

56

78

k (1/Å)0.10

χ(k)Mixture0.08
0.06

Figure 1: EXAFScomparison between
experimental data andFEFF calculation themixture model. a) spolarization b) ppolarization.

0.04

χ(k)

1 Introduction
Pt is a material of fundamental importance in theelectrocatalyst design for polymer electrolyte fuel cells(PEFCs). Electrodeposition advances other varieties ofmethods for Pt thin film deposition, such as MBE, PVD
and so on in the standpoint of view of its simple process,no requirement of UHV environment and lower cost.
Moreover, electrochemical atomic layer deposition (EALD) [1] was one of the most promising
electrodeposition methods to achieve 2D growth of Pt
though 3D Pt clusters were created by the other method.
E-ALD could be applied in growth of a wide range ofmaterials not only Pt but also other metals like Ru, Ag,
Cu etc.[2] However, as the fundamental step in E-ALD
growth of Pt, galvanic displacement using underpotentially deposited Cu or Pd as the sacrificial layer, has
not been fully understood regarding the structure and theelectronic state of the Pt monolayer, which plays
important role in their application as electrocatalyst.
Polarization dependent total reflection fluorescence X-ray
absorption fine structure (PTRF-XAFS) is ideal for
atomic flat, low coverage surface[3].

0.02
0.00
-0.02

2 Experimental
A φ15 mm Au(111)(5 mm thick) single crystal (SPL)
was used as substrate. The Au(111) waselectrochemically polished and flame-annealed and thentransferred into an Ar filled glovebox for further
deposition. A monolayer of Cu was underpotentailly
deposited and then replaced with Pt by immersing thesample into 0.1 M HClO4 + 1 mM H2PtCl6 for 30 s.
Sample was then transferred to the in-situ XAFS cell [4].
6 𝜇 m Mylar film was used as X-ray window. The XAFS
cell was assembled inside the glovebox, and thentransferred to a 5-axis goniometer for total reflection
adjustment. XAFS spectra were measured at BL12C andBL9A, PF. A 19-element Ge solid state detector (MSSD;Canberra) was used as the fluorescence detector. A Znfilter (𝜇𝑡 = 3) was placed in front of the MSSD toremove the elastic scattering from the solution and Au
substrate.
3 Results and Discussion
Figure 1 showed the EXAFS of Pt monolayer obtained
from displacement reaction in both s- and p-polarizations.
FEFF analyses showed that [PtCl4] was the main species

-0.04
-0.06
-0.08
345678k (1/Å)

Figure 2: [PtCl4] with squareplanar structure that parallel tothe Au(111) surface, with Pt
adsorbed on top on Au.

References[1] C.Thambidurai, Y-G. Kim, J.L Stickney,
Electrochimi. Acta, 53, 6157 (2008)[2] N. Dimitrov, Electrochimi. Acta, 209, 599,(2016)[3] Asakura, K.; Chun, W. J.; Shirai, M.; Tomishige, K.;
Iwasawa, Y. J Phys Chem B, 101, 5549 (1997)[4] Q. Yuan, S. Takakusagi, Y. Wakisaka, Y. Uemura, T.
Wada, H. Ariga, K. Asakura, Chem. Lett., 46 (2017)* askr@cat.hokudai.ac.jp