3.3 Electrochemical measurements 59
potential. As an example, imagine a resistance of 40
which is corrected for at
85 %. This leaves 6
unaccounted for which at 10 mA corresponds to 60 mV
lost. In terms of catalytic activity 60 mV can make a large dierence.
3.3.2 Measuring techniques
A range of electrochemical techniques has been used extensively during this
project. For determining catalytic activity cyclic voltammetry has been employed,
while for most stability measurements chronoamperommetry (CA) or
chronopotentiometry (CP) have been used. Cyclic voltammetry is a technique
where the applied potential on the working electrode is cycled between two extremes
at a constant scan rate. This is a useful technique for investigating new
samples and can reveal magnitude and shifts of both irreversible and reversible
redox processes, pseudo-capacitance and catalytic activity of electrodes. The
results of cyclic voltammetry are typically plotted as a voltammogram, where
the current (normalised to area) is a function of the potential applied on the
working electrode. An example of such a voltammogram can be seen in gure
3.12.
Figure 3.12: Cyclic Voltammogram of MnOx in 0.1 M KOH, measured with 20
mV/s in the range 0.05 to 1.7 VRHE. The current is normalised with the geometric
area of the electrode and the potential scale has been corrected for Ohmic losses,
measured with impedance spectroscopy.
From that voltammogram, the electrode can be analysed with respect to
electrochemical properties. The feature around 0.9 VRHE is not reversible as
the oxidation and reduction occur at dierent potentials. If the oxidation peak
can be ascribed to a specic reaction it can also be used to estimate the number