Photon Factory Activity Report 2014 #32 (2015) B

BL-3A/2013G095•2014G124

Potential Dependent Structures at Pt(111)/Electrolyte Solution Interfaces Using In situ
Surface X-ray Scattering
Toshihiro Kondo1,2,*, Takuya Masuda2, Nana Aoki1,2, and Kohei Uosaki2
1
Ochanomizu University, Tokyo 112-8610, Japan2
National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan
1 Introduction
To fully understand the mechanisms of electrochemical
reactions and to apply these reactions to modern
nanotechnology such as fuel cells, sensors, and moleculardevices, it is essential to know the structures at theelectrode/electrolyte interfaces in situ in real time at anatomic level. Surface X-ray scattering (SXS) techniqueusing synchrotron radiation is one of the most promising
methods to investigate the three-dimensional interfacial
structures in situ with an atomic dimension. Using thistechnique, we have investigated various interfacial
structures such as Au single crystal electrode/sulfuric acidinterface [1,2], electrodeposited Pd, Ag, and Pt onAu(111) electrode [3-7], and underpotentially deposited
Ag bilayer on Au(111) during Ag/AgCl reaction [8].
Pt is one of the most useful electrocatalytic materials
and then it is of great importance to investigate thestructure at Pt single crystal electrode/electrolyte interface
under electrode potential control in situ. Here we reported
to investigate the potential dependent structures atPt(111)/electrolyte solution interfaces by using in situ
SXS technique.
2 Experiment
Prior to SXS measurements, Pt(111) disk was annealed
at 1600 °C for more than 2 h under argon/hydrogen
atmosphere using an induction heater and quenched with
an ultrapure water under an argon/hydrogen atmosphere.
The electrochemical cell for the SXS measurements wasfilled with a deaerated 0.1 M HClO4 or 0.05 M H2SO4
electrolyte solution under electrode potential control.
After that, the cell was set to the 6 axes diffractomator,
which was installed at the undulator-magnet beamline
BL3A, and in situ SXS measurements were carried out atvarious potentials, where distinguishing current waves
were measured in the cyclic voltammograms (CVs). An
energy of 12 keV was selected.
3 Results and Discussion
By fitting the (00) rod data to theoretical three-layered
model, the interfacial structures were determined.
In 0.1 M HClO4 solution, at -0.05 V (vs. Ag/AgCl) and+0.12 V, where hydrogen underpotential deposition(UPD) current continued to flow and just finished to flow,
respectively, in the CV, a layer distance between theoutermost and second outermost Pt layers was expandedby ca. 3.5 %. At +0.30 V just more negative than thepotential where oxidation current started to flow, several
oxygen species such as water and/or perchlorate anion

were randomly adsorbed on the Pt(111) surface. The layer
distance between the outermost and second outermost Pt
layers was relaxed to that of the same distance as bulk Pt.
At +0.55 V, where the oxidation spike was observed inthe CV, oxygen species which maybe hydroxide anion
were adsorbed on the Pt(111)-(1×1) surface with ap(2×2)_3O structure. At +0.65 V, where the pre-oxidation
current peak just finished to flow in the CV, oxygen
species which maybe hydroxide anion were adsorbed at
an atop site of the Pt(111)-(1×1) surface with a (1×1)
structure. Potential dependent dynamics of the interfacial
structures were now under investigation.
In 0.05 M H2SO4, on the other hand, at -0.05 V (vs.
Ag/AgCl) and +0.12 V, where hydrogen UPD current
continued to flow and just finished to flow, respectively,in the CV, the layer distance between the outermost andsecond outermost Pt layers were expanded by ca. 3.5 %,as well as in the case in 0.1 M HClO4. At +0.30 V in thedouble layer potential region, several oxygen species suchas water and sulfonate anion were adsorbed on thePt(111) surface. At +0.65 V, where the pre-oxidation
current peak just finished to flow in the CV, oxygen
species which maybe hydroxyl anion were adsorbed atthe atop site of the Pt(111) surface with the (1×1)
structure. Potential dependent dynamics of the interfacial
structures were now under investigation.
Acknowledgement
This work was supported by and conducted at theGlobal Research Center for Environment and Energy
based on Nanomaterials Science (GREEN) in NIMS.
References[1] T. Kondo et al., J. Phys. Chem. C 111, 13197 (2007).
[2] T. Kondo et al., Surf. Sci. 631, 96 (2015).
[3] M. Takahasi et al., Surf. Sci. 461, 213 (2000).
[4] T. Kondo et al., J. Electroanal. Chem. 532, 201(2002).
[5] T. Kondo et al., Electrochim. Acta 55, 8302 (2010).
[6] M. Takahasi et al., J. Phys.: Condens. Matter 22,474002 (2010).
[7]M. Shibata et al., J. Phys. Chem. C 116, 26464 (2012).
[8] K. Uosaki et al., J. Phys. Chem. C 115, 12471 (2011).