An atomic scale understanding of the surface degradation
mechanism
during cathodic corrosion of a platinum electrode is still lacking.
Here, we present results of surface structural changes observed during
cathodic polarization of a polycrystalline Pt electrode and single
crystalline Pt(111) in acid electrolytes in the absence and presence
of cations (Na+) byin situelectrochemical
atomic force microscopy (EC-AFM) imaging. The electrolyte cation is
proved to be a prerequisite to trigger cathodic etching of the polycrystalline
Pt surface. Further examination of the evolution of electrochemical
signals and distinct surface structural transformations of an atomically
defined Pt(111) single-crystal electrode during cathodic corrosion
reveals clearly that the roughening process commences at the under-coordinated
sites of the Pt(111) surface. The created triangular-shape pattern,
actually a 100-oriented pit in a 111-terrace, grows primarily laterally
in the initial regime, while prolonged cathodic corrosion leads to
the existing etching pits growing in depth until ultimately they coalesce
with each other, generating a highly roughened surface.