Ab Initio Atomistic Thermodynamics for Fuel Cell Catalysis - Fuel Cell Catalysis: A Surface Science Approach - page 148

Figure 5.9 Schematic cyclic voltammogram showing the electro-oxidation of the electrode
(dashed box). The curve was generated from measurements by Jerkiewicz et al. [2004] of Pt in
0.5 M H 2 SO 4 with a reversible hydrogen reference electrode (RHE). For each separable potential
range, an atomistic model of the electrode structure is shown above.
After forming an adsorbate layer of oxygen or an O-containing species on the elec-
trode surface, the persistent current density that can be observed at higher electrode
potentials is usually attributed to the formation of a surface oxide, which, after a certain
time, continues growing to finally form the bulk oxide. While different electrochemi-
cal techniques [Gilroy and Conway, 1968; James, 1969; Kim et al., 1971; Allen et al.,
1974] show evidence of the formation of an oxide, even for the standard system of Pt
in contact with an aqueous solution, the exact structure and thickness of this oxide is
still unclear [Dickinson et al., 1975; You et al., 1994; Clavilier et al., 1996; Jerkiewicz
et al., 2004]. Here, the common view is that oxide growth first begins with the for-
mation of a thin layer of PtO composition, onto which an oxide of PtO 2 composition
continues growing.
Before we can apply the extended ab initio atomistic thermodynamics approach to
the oxygen-covered surface or the surface/bulk oxide, we have to investigate the struc-
ture of the bulk electrode.
5.3.3 Morphology of the Bulk Electrode (Stability Condition)
While at low electrode potentials the bulk electrode will be purely platinum, at high
positive electrode potentials the cyclic voltammogram shows that it becomes an