DISSERTATION

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Results and Discussion
3.2.2 Potential of zero charge of bare and DNA-modified electrodes
Theoretical discussions were done with Dr. Fabio La Mantia. Parts of this section were
published in ref. 5 : “D. Jambrec, M. Gebala, F. La Mantia, W. Schuhmann, Angew. Chem. Int.
Ed. 2015, 54, 15064-15068; Angew. Chem. 2015, 127, 15278-15283.”.
The potential of zero charge is a fundamental property of an electrode-electrolyte interface.
Therefore, for the in-depth understanding of the surface behavior it is of high importance to
know the value of the pzc. At the pzc the excess charge density on the electrode surface equals
zero 76,77 . The term “potential of zero free charge” (pzfc) is also used for the same value in order
to differentiate it from the so-called potential of zero total charge (pztc) that refers to the case
when a specific adsorption occurs on the interface involving charge transfer. The pztc is defined
as a potential at which the sum of free electronic excess charge density and charge density
transferred in the adsorption processes equals zero 76 . In order to better understand these terms,
three different situations at the electrode-electrolyte interface are shown in Figure 3.11, when
the applied potential equals pz(f)c, pztc or any other value.
In the literature there is a substantial variation of reported values for the pzc of gold electrodes 78 .
Due to the polycrystalline nature of the Au surface, the use of different electrolyte solutions and
the fact that the pzc is very sensitive to surface impurities, many different values were proposed.
Therefore, we determined the pzc for our system with thoroughly cleaned Au electrodes in the
same solution that was later used for the modification of the surface.
The most common way to determine the pzc is to find the minimum of the differential
capacitance in the Cd-E curve, predicted by the GC theory 77 . It should be noted that for systems
in which specific adsorption occurs the capacitance minimum provides the value of the pztc.
Since we used a solution that contains sulfates, the obtained value evidently represents the pztc.
However, for convenience of the readers, the general term pzc is used in the following text.
Based on the definition, the pzc can be described by equation 3.1:
σ m = dC d
dE = 0 (3.1)
3.2 Importance of knowing the surface 41