Abstract
AbstractCO adlayers on Pt(111) electrode surfaces are an important electrochemical system and of great relevance to electrocatalysis. The potential‐dependent structure and dynamics of these adlayers are complex and still controversial, especially in the CO pre‐oxidation regime. We here employ in situ high‐speed scanning tunneling microscopy for studying the surface phase behavior in CO‐saturated 0.1 m H2SO4 on the millisecond time scale. At potentials near the onset of CO pre‐oxidation local fluctuations in the (2×2)‐CO adlayer are observed, which increase towards more positive potentials. Above 0.20 V (vs. Ag/AgCl), this leads to an adlayer where COad apparently reside on every top site, but still exhibit a (2×2) superstructure modulation. We interpret this observation as a dynamic effect, caused by a small number of highly mobile point defects in the (2×2)‐CO adlayer. As shown by density functional theory calculations, the CO lattice near such defects relaxes into a local (1×1) arrangement, which can rapidly propagate across the surface. This scenario, where a static (2×2) COad sublattice coexists with a highly dynamic sublattice of partially occupied top sites, explains the pronounced COad surface mobility during electrooxidation.
Highlights
CO adlayers on Pt(111) electrode surfaces are an important electrochemical system and of great relevance to electrocatalysis
We here employ in situ high-speed scanning tunneling microscopy for studying the surface phase behavior in CO-saturated 0.1m H2SO4 on the millisecond time scale
At potentials near the onset of CO preoxidation local fluctuations in the (2 2)-CO adlayer are observed, which increase towards more positive potentials
Summary
CO adlayers on Pt(111) electrode surfaces are an important electrochemical system and of great relevance to electrocatalysis. In situ studies by STM,[4] infrared spectroscopy,[5] sum frequency generation (SFG),[6] as well as density functional theory (DFT) calculations[7] have found a significant potential dependence of the COad adsorption sites and the resulting CO adlayer structure on Pt(111) electrodes.
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