Chemistry Reference
In-Depth Information
2
3
4
1
5
12.6
Scheme of the flow-through cells with (1) [Fe(II)TSPc]
4
-
modified
carbon-fibre electrode, (2) glass tubes to immobilise the carbon
fibre, (3) reference electrode, (4) flow-through pipeline and (5)
metallic tube acting as counter electrode.
12.3.3 Electrodeposition of [Fe(II)TSPc]
4
-
in pH
=
7.4 buffer
at carbon fibres
In Fig. 12.7, the electrodeposition of [Fe(II)TSPc]
4-
(Fig. 12.8) is shown as a
function of scan number and was carried out in a 1 ¥ 10
-3
mol l
-1
[Fe(II)TSPc]
4-
solution. Five peaks could be observed during this experi-
ment; all of them were increasing with scan number (some of them
increased weakly). This means that indeed [Fe(II)TSPc]
4-
is being deposited
onto the surface of the carbon fibre. Extensive research on [Fe(II)TSPc]
4-
can be found in the literature
47-53
.The paper by Zecevic
et al.
50
was used as
reference work to identify the observed peaks. However, their study showed
that no peaks were observed in the first scan using [Fe(II)TSPc]
4-
. Around
0V vs. Ag|AgCl in Fig. 12.7, a broad oxidation peak was obtained attributed
to Fe
II
/Fe
III
oxidation. The return peak for this oxidation was observed at
-0.5 V vs. Ag|AgCl (A). A second weak redox couple (B) is attributed to
ring oxidation in the [Fe
III
TSPc(-2)]
3-
, giving [Fe
III
TSPc(-1)]
2-
.A relatively
large irreversible reduction peak (C), centered around 0.2 V vs. Ag|AgCl,
could be identified as the reduction of oxygen. Despite the fact that the
experiments were carried out in solutions purged with nitrogen, oxygen was
produced at the fibre surface at the most positive applied potentials. Scan-
ning the potential to a value less positive than the oxygen-evolution reac-
tion (up to 1.25 V vs. Ag|AgCl) did not result in peak C. Therefore, it could
be concluded that this peak was due to oxygen reduction.
