DISSERTATION

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Results and Discussion
C d = 1
(3.4)
2πfZ
′′
where ω is the angular frequency.
Figure 3.13. Example of a Nyquist plot used for the system characterization and
calculation of Cd. The presented curve was recorded for a potential of 0.8 V vs. Pb/PbF2/5
M KF (0.2 V vs. Ag/AgCl/3 M KCl) in the frequency range from 4 kHz to 100 Hz. The
measurement was performed in 10 mM PB with 20 mM K2SO4. A capacitive bridge (2 µF)
was used. The beige line represents the fit to the RC equivalent circuit.
Figure 3.14 shows the obtained Cd values for three electrolyte solutions of different ionic
strengths calculated at three different frequencies. Comparing different ionic strengths, no clear
minimum is observed (Figure 3.14, a-c). On the contrary, for the highest ionic strength a
maximum was observed in one part of the curve. This behavior was previously observed for
high ionic strength electrolytes 83 . Furthermore, looking at the individual ionic strength, the
same trend can be observed for all three chosen frequencies. However, when different ionic
strengths for the same frequency are compared (Figure 3.14, d-f), the biggest difference is
observed between different ionic strengths for a frequency of 100 Hz (Figure 3.14, d).
3.2 Importance of knowing the surface 45