Biomedical Engineering Reference
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by Ludi and coworkers from single crystals by electron and neutron diffraction meas-
urements [6]. Prussian blue has a basic cubic structure consisting of alternating iron(II)
and iron(III) located on a face centered cubic lattice (Fig. 13.1), in such a way that the
iron(III) ions are surrounded octahedrically by nitrogen atoms, and iron(II) ions are sur-
rounded by carbon atoms. The cubic unit cell dimensions are of 10.2Å.
13.2.2 Electrochemistry of transition metal hexacyanoferrates
Commonly, deposition of Prussian blue on various conductive surfaces is carried out
from the aqueous solutions containing a mixture of ferric (Fe
3
) and ferricyanide
([Fe
III
(CN)
6
]
3
) ions, either spontaneously in open-circuit regime or by applying a
reductive electrochemical driving force. Chronopotentiometric investigations in equi-
molar ferric-ferricyanide mixtures has shown the two basic plateaus: at 0.7 V and at
0.4 V (SCE) [7]. These plateaus have been attributed to reduction of the one-to-one
complex of Fe
III
[Fe
III
(CN)
6
], discovered earlier [8], and of Fe
3
ions, respectively. At
0.7 V Prussian blue is deposited according to reduction of the ferric-ferricyanide com-
plex (Fe
III
[Fe
III
(CN)
6
]). Around 0.4 V the bulk precipitation of Prussian blue occurs due
to reduction of Fe
3
to Fe
2
, the latter reacts with ([Fe
III
(CN)
6
]
3
). The open-circuit
deposition is highly dependent on the electrode support. Its mechanism is probably
the oxidation of the conductive material with the (Fe
III
[Fe
III
(CN)
6
]) complex, which
forms Prussian blue after one-electron reduction. Posing of the electrodes to the poten-
tials lower than 0.2 V is, according to our experience, not plausible for deposition of
Prussian blue, because both Fe
3
and [Fe
III
(CN)
6
]
3
ions are reduced, and the structure
of the resulting polycrystal is less regular.
A cyclic voltammogram of a Prussian blue-modifi ed electrode is shown in Fig.
13.2. In between the observed two sets of peaks the oxidation state, which is corre-
spondent to the Prussian blue itself, occurs. Its reduction is accompanied with loss of
FIGURE 13.1
Prussian blue unit cell according to Keggin and Miles, plotted using data from measure-
ments [6]; (
) Fe
3
, (
) Fe
2
.
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