Chemistry Reference
In-Depth Information
17
6
5
4
12
3
2
7
1
2
0
0.1
0.2
0.3
0.4
0.5
0.6
E
(V) vs. SCE
-3
7.7
Voltammetric curves of sodium dithionite at a bare gold electrode
(curves 1 and 4), at a CoTSPc-modified gold electrode (curves 2
and 5) and at a CoTSPor-modified gold electrode (curves 3 and 6),
in pH
=
12 buffer solution containing 9.85
¥
10
-
4
(curves 1, 2 and 3)
and 1.46
¥
10
-
3
mol l
-
1
(curves 4, 5 and 6) of sodium dithionite.
T
=
298.0 K;
v
=
50 mV s
-
1
.
overpotential (or generally activation energy) should be applied to the
system because of the presence of CoTSPc that provides an alternative, less
energy demanding, oxidation reaction path for sodium dithionite. Secondly,
the slope of the inclining part of the wave is higher at the modified elec-
trodes, revealing faster charge-transfer kinetics. Thirdly, the shape of the
voltammetric wave is better defined (more peak-shaped wave), and the
peak currents are higher compared with the peak currents obtained at an
unmodified electrode. Finally, experiments with varying concentrations of
sodium dithionite at gold electrodes and CoTSPc-modified gold electrodes
(Fig. 7.8) showed that the peak current shift towards more positive poten-
tials is much more expressed at unmodified gold electrodes than is the case
at the modified ones. This again indicates that, for the modified electrodes,
the influence of the charge-transfer kinetics in the overall oxidation rate
is smaller. Important to note is that the oxidation of sodium dithionite at
the modified gold electrodes is still behaving irreversibly, so charge-
transfer kinetics still play a role in the overall rate, particularly at low
overpotentials.
Another remark is the relatively mild electrocatalytic effect resulting in
a shift of the wave of 20 mV and an increase of the peak currents by approx-
