46
2 Methods for Investigating Electro-Chemo-Mechanical …
Fig. 2.6 Schematic two-coupled |A| vs. E and q vs. E (a, b and a , b ) curves in the vicinity of
E pzc for two electrolyte solutions with different concentrations for calibration of the conversion
coefficient K [5]. Modified with the permission from [5], Copyright 1998, American Chemical
Society
−
∂g 4
∂E
= q 4 +
∂q 4
∂ε
.
(2.7)
Then, K may be written in place of Eq. (2.5):
K =
−
∂g 2
∂E
+
∂g 1
∂E
−
−
∂g 4
∂E
+
∂g 3
∂E
(|A 2 | − |A 1 |) − (|A 4 | − |A 3 |)
.
(2.8)
There are unknown parameters to determine K from Eq. (2.8). The term of
∂q
∂ε
is elastic by nature and is not influenced by a diffuse part of the electric double layer
which is purely plastic because it is located in liquid phase. In addition, the variation
of the electrolyte concentration (at least below 0.1 M) does not affect the structure
of the compact (inner Helmholtz) part of the electric double layer near E pzc . This
leads to the reasonable assumption that
∂q 2
∂ε
−
∂q 1
∂ε
and
∂q 4
∂ε
−
∂q 3
∂ε
are independent