Electrochemical Oxidation of Smooth and Nanoscale Rough Pt(111): An In Situ Surface X-ray Scattering Study

Abstract

The potential dependent surface structure of Pt(111) electrodes in electrochemical environment was studied by in situ crystal truncation rod measurements and in operando grazing incidence small angle X-ray scattering. Determination of the interface structure in the oxidation region reveal a continuous increase of the coverage of place exchanged atoms toward more positive potentials. The resulting oxide consists of an oxygen rich outer and a Pt-rich inner atomic layer. With increasing potential the oxide approaches a more uniform stoichometry. While place exchange on atomically smooth terraces only occurs above 1.05 V, structural changes of 3D Pt islands, grown by repetitive oxidation/reduction cycles, already commence at 0.8 V, which is assigned to oxidation at Pt steps. Evolution of the 3D island distribution occurs in all stages of the cycles: Whereas Pt oxidation leads to narrowing of the lateral size distribution, vertical island growth occurs during the subsequent reduction.

Pt oxide and oxygen reduction at Pt(111) studied by surface X-ray diffraction

“…However, their X-ray absorption near edge structure (XANES) measurements on Pt nanoparticles suggested that the PE mechanism commences as soon as 0.75 V. These XANES observations could be due to a different oxidation reactivity associated with the finite size as well as the presence of other crystal facets and step sites on the nanoparticles. Indeed, GISAXS measurements of nanoscale roughened Pt(111) surfaces also provided evidence of the surface oxidation shift to lower potentials, which was attributed to the step edge oxidation [37].…”

Correlation of surface site formation to nanoisland growth in the electrochemical roughening of Pt(111)

“…Initially both {100} and {111} steps (more precisely, these step sites should be denoted as < 110 > /{100} and < 110 > /{111} respectively, that is, steps along a direction equivalent to [110] and exhibiting a square {100} or hexagonal {111} geometry) form on the roughened surface, while eventually only {111} steps remain. Advanced in situ EC-STM 16,17 and X-ray reflectivity [18][19][20][21][22] experiments are ideal tools to study this system at the atomic level. Using X-ray scattering experiments, and following the surface evolution for 20 ORCs, Ruge et al observed an increasing island size with increasing cycle number and decreasing upper potential limit 21 .…”

Nanoscale morphological evolution of monocrystalline Pt surfaces during cathodic corrosion

“…In contrast, monocrystalline electrodes are the surfaces of choice to study the atomic scale’s structural transformation process ( 18 , 19 ). Studying cathodic corrosion on monocrystalline surfaces allows tracking the changes from a well-defined atomic structure to a corroded (roughened) surface and correlates the surface etch patterns obtained in the polycrystalline and monocrystalline electrode ( 20 – 23 ). Such an atomistic understanding may ultimately guide approaches to avoid cathodic corrosion or to design procedures to make tailored nanoparticles via cathodic corrosion.…”