28
1 Surface Thermodynamics of Solid Electrode
0.45
0.40
0.35
0.30
0.25
/ J m
-2
-1.0
-0.5
0.0
0.5
(E - E pzc ) / V
Hg / electrolyte
KOH
NaCl
NaBr
KI
Fig. 1.6 Electrocapillary curves measured for the mercury electrode in electrolyte solutions
containing various anions [30]. Reprinted with the permission from [30], Copyright 1947, American
Chemical Society
as a function of potential, the electrocapillary curve of the solid electrode can be
obtained by using Eq. (1.130) or Eq. (1.131) under the condition that the last term in
the right-hand side of Eq. (1.112); i.e., (g − γ )
∂ε
∂E
T ,μ i
is neglected. Figure 1.8 shows
the surface charge density versus potential (q vs. E) curves for an unreconstructed
Au (111) electrode in 0.1 M HClO 4 solutions without and with 10
−5 M, and 5 ×
10
−3 M K 2 SO 4 [32]. The potential in the abscissa of Fig. 1.8 is referred to a saturated
calomel electrode (SCE), the potential of which is more positive by 0.241 V than
that of a standard hydrogen electrode (SHE). Since the absolute value of γ for a solid
electrode cannot be measured experimentally, the integration of the charge density
data (in Fig. 1.8) with respect to potential is made from −0.20 V (SCE) to the
positive direction to obtain the changes in surface tension γ , referred to zero at −
0.20 V (SCE). Figure 1.9 shows the electrocapillary curves ((γ vs. E) thus obtained
for the unreconstructed Au (111) electrode [32]. The electrocapillary curves merge
at E < 0.20 V (SCE) and diverge at more positive potentials where γ decreases
with increasing bulk SO 4
2− concentration, indicating that the adsorption of sulfate
proceeds significantly at E > 0.20 V (SCE). As explained above, the electrocapillary
curve ((γ vs. E) for a solid electrode can be obtained from the data of the differential
capacity or surface charge density measured as a function of potential.
1.10 Surface Stress versus Potential Curve of Solid Metal
Electrode
It is unable to measure the absolute value of the surface stress as well as the surface
tension for a solid metal electrode. Nevertheless, the changes in surface stress can be
1 Surface Thermodynamics of Solid Electrode
0.45
0.40
0.35
0.30
0.25
/ J m
-2
-1.0
-0.5
0.0
0.5
(E - E pzc ) / V
Hg / electrolyte
KOH
NaCl
NaBr
KI
Fig. 1.6 Electrocapillary curves measured for the mercury electrode in electrolyte solutions
containing various anions [30]. Reprinted with the permission from [30], Copyright 1947, American
Chemical Society
as a function of potential, the electrocapillary curve of the solid electrode can be
obtained by using Eq. (1.130) or Eq. (1.131) under the condition that the last term in
the right-hand side of Eq. (1.112); i.e., (g − γ )
∂ε
∂E
T ,μ i
is neglected. Figure 1.8 shows
the surface charge density versus potential (q vs. E) curves for an unreconstructed
Au (111) electrode in 0.1 M HClO 4 solutions without and with 10
−5 M, and 5 ×
10
−3 M K 2 SO 4 [32]. The potential in the abscissa of Fig. 1.8 is referred to a saturated
calomel electrode (SCE), the potential of which is more positive by 0.241 V than
that of a standard hydrogen electrode (SHE). Since the absolute value of γ for a solid
electrode cannot be measured experimentally, the integration of the charge density
data (in Fig. 1.8) with respect to potential is made from −0.20 V (SCE) to the
positive direction to obtain the changes in surface tension γ , referred to zero at −
0.20 V (SCE). Figure 1.9 shows the electrocapillary curves ((γ vs. E) thus obtained
for the unreconstructed Au (111) electrode [32]. The electrocapillary curves merge
at E < 0.20 V (SCE) and diverge at more positive potentials where γ decreases
with increasing bulk SO 4
2− concentration, indicating that the adsorption of sulfate
proceeds significantly at E > 0.20 V (SCE). As explained above, the electrocapillary
curve ((γ vs. E) for a solid electrode can be obtained from the data of the differential
capacity or surface charge density measured as a function of potential.
1.10 Surface Stress versus Potential Curve of Solid Metal
Electrode
It is unable to measure the absolute value of the surface stress as well as the surface
tension for a solid metal electrode. Nevertheless, the changes in surface stress can be