110
4 Changes in Surface Stress Associated with Underpotential …
of g in the absence of Pb
2+ varies monotonously with potential in both cathodic
and anodic potential scans. It is known that the potential of zero charge E pzc for
the unreconstructed Au (111) electrode in perchloric acid is 0.48 V (SHE) [21].
Therefore, the surface tension γ of the Au (111) electrode should take a maximum at
0.48 V (SHE). On the other hand, the g vs. E curve in the absence of Pb
2+ does not
take a maximum in the potential region between −0.24 V and 0.80 V (SHE), which
is consistent with that reported by Stafford and Bertocci [13]. The g vs. E curve
in the presence Pb
2+ has maxima at about 0.2 V and humps at about −0.05 V (SHE)
in both cathodic and anodic potential scans. These maxima and humps correspond
to the C 1 /A 1 current peaks and the C 2 /A 2 and C 3 /A 3 current peaks, respectively, in
the cyclic voltammogram (Fig. 4.3a), which are associated with electrodeposition
(UPD) of Pb
2+ and with anodic stripping of electrodeposited Pb. The g vs. E curve
in the presence of Pb
2+ indicates that g decreases toward compressive direction
with the progress in Pb-UPD at potentials more negative than 0.2 V (SHE). The
humps at about - 0.05 V (SHE) result from the structural changes of the Pb-UPD
layer as discussed later. The difference (g) between the changes in surface stress
in the solutions without and with Pb
2+ attains to −1.07 J m
−2 at a cathodic limit
potential of −0.24 V (SHE).
Figure 4.4 shows the relationship between changes in surface stress g and
cathodic charge density q c derived from the results of Fig. 4.3 [12]. The value
of g is taken in the cathodic potential scan from 0.80 V (SHE), while the value
Fig. 4.4 Relationship between changes in surface stress g and cathodic charge density q c
derived from the results of Fig. 4.3 [12]. The value of g is taken in the cathodic potential scan
from 0.80 V (SHE), while the value of q c is obtained from the integration of the corresponding
cyclic voltammogram, referred to zero at 0.80 V (SHE). The surface coverage θ Pb of Pb on the top
abscissa of Fig. 4.4 is calculated from the cathodic charge density by regarding as θ Pb = 1.0 at −
0.24 V (SHE). Reproduced from [12] with permission from The Electrochemical Society
4 Changes in Surface Stress Associated with Underpotential …
of g in the absence of Pb
2+ varies monotonously with potential in both cathodic
and anodic potential scans. It is known that the potential of zero charge E pzc for
the unreconstructed Au (111) electrode in perchloric acid is 0.48 V (SHE) [21].
Therefore, the surface tension γ of the Au (111) electrode should take a maximum at
0.48 V (SHE). On the other hand, the g vs. E curve in the absence of Pb
2+ does not
take a maximum in the potential region between −0.24 V and 0.80 V (SHE), which
is consistent with that reported by Stafford and Bertocci [13]. The g vs. E curve
in the presence Pb
2+ has maxima at about 0.2 V and humps at about −0.05 V (SHE)
in both cathodic and anodic potential scans. These maxima and humps correspond
to the C 1 /A 1 current peaks and the C 2 /A 2 and C 3 /A 3 current peaks, respectively, in
the cyclic voltammogram (Fig. 4.3a), which are associated with electrodeposition
(UPD) of Pb
2+ and with anodic stripping of electrodeposited Pb. The g vs. E curve
in the presence of Pb
2+ indicates that g decreases toward compressive direction
with the progress in Pb-UPD at potentials more negative than 0.2 V (SHE). The
humps at about - 0.05 V (SHE) result from the structural changes of the Pb-UPD
layer as discussed later. The difference (g) between the changes in surface stress
in the solutions without and with Pb
2+ attains to −1.07 J m
−2 at a cathodic limit
potential of −0.24 V (SHE).
Figure 4.4 shows the relationship between changes in surface stress g and
cathodic charge density q c derived from the results of Fig. 4.3 [12]. The value
of g is taken in the cathodic potential scan from 0.80 V (SHE), while the value
Fig. 4.4 Relationship between changes in surface stress g and cathodic charge density q c
derived from the results of Fig. 4.3 [12]. The value of g is taken in the cathodic potential scan
from 0.80 V (SHE), while the value of q c is obtained from the integration of the corresponding
cyclic voltammogram, referred to zero at 0.80 V (SHE). The surface coverage θ Pb of Pb on the top
abscissa of Fig. 4.4 is calculated from the cathodic charge density by regarding as θ Pb = 1.0 at −
0.24 V (SHE). Reproduced from [12] with permission from The Electrochemical Society