DISSERTATION

________________________________________________________________ Experimental Work
directions equally, allowing the formation of homogenous surfaces. The procedure was
controlled by a home-made software. Polishing clothes were soaked in water prior to polishing
and covered homogeneously with an appropriate polishing paste. Electrodes were polished with
diamond pastes of 3, 1, 0.5 and 0.1 µm particle size successively, using separate polishing cloths
for each paste. Polishing time depended on the state of the electrode.
Afterwards, the gold electrodes were electrochemically cleaned by cyclic voltammetry in 0.5
M H2SO4 until reproducible voltammograms were obtained. Cycling was performed in the
potential range of 0 V to 1.6 V vs. Ag/AgCl (3 M KCl) at 100 mV/s scan rate. The roughness
factor was kept around 1.4 and its determination was done according to 111 . The method is based
on the determination of oxygen adsorption on a gold surface. During a positive potential scan
chemisorption of oxygen occurs, where different gold facets have different oxidation potentials
(Figure 5.3). During the negative potential scan oxides are reduced, which can be seen as a
single reduction peak. Assuming that oxygen atoms form a monolayer on the gold surface, the
roughness factor of an electrode can be determined using the following equations:
R = A real
A g
(5.1)
A g = r 2 π (5.2)
A real = Q exp
Q theor
(5.3)
Q exp =
peak area
ν
(5.4)
where Ag is the geometrical surface area of the electrode (0.0314 cm 2 for a 2 mm diameter gold
electrode), Areal is the real surface area, Qexp is the charge involved in the reduction of gold
oxide, Qtheor is 482 μC/cm 2 and it is a calculated charge value for chemisorption of an oxygen
monolayer on the surface of polycrystalline gold, based on the density and atomic weight of
gold 112 , υ is the scan rate of the measurement and peak area is the area under the reduction peak
from the CV measurement obtained by integration of the peak (Figure 5.3, area marked in
green).
After mechanical polishing and electrochemical cleaning, the electrodes were immediately
characterized by EIS and CV to verify their cleanliness prior to modification (procedures
explained in Sections 5.9.1 and 5.9.2, respectively).
112