Chemistry Reference
In-Depth Information
Z
1
Z
1
Z
2
Z
2
Z
3
Z
3
Z
n
Z
n
(a)
(b)
9.11
Schematic representation of two sets of electrodes of palladium
(a) and textile electrode (b) and the influence of roughness of the
electrode surface on the measured impedance (
Z
).
locations at the electrode surfaces. This is shown schematically and in a
somewhat simplified form in Fig. 9.11. Contrary to the palladium electrodes,
the surface of textile structures is not flat, particularly for the non-woven
structures. Therefore, the experimental impedance is the sum of the indi-
vidual local impedances:
=
Â
1
Z
[9.8]
n
n
is not equal to
n
times
Z
1
or
Z
2
or
Z
n
because of differences in local dis-
tances between the textile electrodes. This is not the case for the flat palla-
dium electrode where
Z
1
=
Z
2
=
Z
3
=
Z
n
. Larger differences in the values of
Z
1
,
Z
2
,
Z
3
, to
Z
n
result in wider error margins, an effect that is clearly
observed for the non-woven structure and is related to the high degree of
roughness compared with the knitted and woven structure and to the flat
palladium electrode surfaces.
The cause of the second observation should be sought by examing the
way in which the electrodes are positioned in the electrochemical cell. In
Fig. 9.12, the positioning of a palladium electrode (a) and a woven (b) and
knitted (c) textile electrode at one side of the electrochemical cell is pre-
sented. Note that these drawings represent cross-sections. It must also be
mentioned that the structure of the knitted electrode is relatively elastic,
which is typical for knitted structures, while the structure of the woven elec-
trode is tight and rigid. This effect can explain the shifts of the calibration
curves. For a woven structure, the measurement of
Z
will be somewhat
higher compared with the palladium electrode, because a large fraction of
