Photon Factory Activity Report 2017 #35 (2018)

BL-9A/2017G156

Revisit of Pt Deposition via Surface Limited Redox Replacement of Copper UPD
Layer on Au(111) by EXAFS
Qiuyi Yuan,1 Yuki Wakisaka,1 Yohei Uemura,2 Takahiro Wada,3 Hiroko Ariga-Miwa,1 Satoru
Takakusagi,1 Kiyotaka Asakura1* and Stanko R Brankovic4
1Intitute for Catalysis, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo, Hokkaido 0010021, Japan
2
Institute for Molecular Science, Okazaki, Aichi 444-0867, Japan
3Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
4
Department of Electrical and Computer Engineering, University of Houston, Houston, Texas,
77204-4005, USA

1 Introduction
Two-dimensional (2D) Pt thin films have been used invariety of applications in recent years. A new deposition
method, called as SLRR (Surface Limited RedoxReplacement)
was developed based on UPD
monolayer serving as a reducing sacrificial template in agalvanic displacement reaction with more noble Pt ions[1].
The deposition protocol involves several steps in which theAu surface (substrate) is first covered with a UPD layer ofCu which plays a role as sacrificial metal and wasdisplaced with Pt under open circuit potential (OCP).
We reported that [PtCl4] was a main and initial productafter the SLRR which was totally different from theoriginal pictures[1].
After the critical discussion werevisted the XAFS analysis and now we proposed anothernew model structure that satisfied all characterization
results including XAFS[2].
2 Experiment
A φ15 mm Au(111)(5 mm thick) single crystal (SPL)
was used as substrate. The Au(111) was electrochemicallypolished and flame-annealed and then transferred into anAr filled glovebox for further deposition. A monolayer ofCu was underpotentially deposited which was thenreplaced with Pt by immersing the sample into 0.1 M
HClO4 + 1 mM H2PtCl6 for 30 s. sample was thentransferred to the in-situ XAFS cell. 6 m Mylar film wasused as X-ray window. The XAFS cell was assembled
inside the glovebox filled with N2, and then transferred toa 5-axis goniometer for total reflection adjustment. XAFS
spectra were measured at BL12C and BL9A, PF. A 19element Ge solid state detector (MSSD; Canberra) wasused as the fluorescence detector. A Zn filter (3) was
placed in front of the MSSD to remove the elastic
scattering from the solution and Au substrate.
3 Results and Discussion
Previous EXAFS analysis clearly showed that PtCl4
complex was present with Pt-Cl =0.226 nm parallel to theAu surface[2]. However, we assumed the mixture modelof PtCl4 and Pt nanoclusters as shown in Fig .1 where PtPt was wqual to 0.288 nm, Pt-Au was 0.282 nm and total
particle size was 2.2 nm. The PtCl4 to Pt ratio was 2:3.
Figure 2 shows the comparison between the observed andcalculated EXAFS oscillations in parallel andperpendicular directions. This structure was consistent
with XPS, AFM and cyclic voltammetry results
We concluded the mixture Pt species present on the Au
surface after the SLRR.[3]Fig. 1: Proposed model structure(a)(b)

Fig.2 XAFS oscillations (a) ⃗ ∥ surface (b) ⃗ ⊥ surface[1] Brankovic, S. R., Wang, J. X. & Adzic, R. R. (2001).
J.Serb.Chem.Soc. 66, 887-898.
[2]Yuan, Q., Takakusagi, S., Wakisaka, Y., Uemura, Y., Wada,T., Ariga, H. & Asakura, K. (2017). Chem. Lett. 46, 1250-1253.
[3] Yuan, Q., Wakisaka, Y., Uemura, Y., Wada, T., ArigaMiwa, H., Takakusagi, S., Asakura, K. & Brankovic, S. R.
(2017). Submitted to J.Phys,Chem, C.

* askr@cat.hokuda.ac.jp