Biomedical Engineering Reference
In-Depth Information
(a)
(b)
12
400
320
8
240
160
4
320 Hz
0.15 Hz
80
5.0 kHz
0
0
0
80
160
240
320
400
0
4
8
12
Z'
(Ω cm
2
)
Z'
(Ω cm
2
)
FIGURE 4.26
The Nyquist plots for the BDD electrode in K
4
Fe(CN)
6
+ H
2
SO
4
aqueous solution after (a) anodic pretreatment at
3.0 V or (b) cathodic pretreatment at -3.0 V. Frequency intervals: 50 kHz to 30 MHz (a) and 50 kHz to 10 Hz (b).
Measurements carried out at 0.60V. (From Suffredini, H.B.,
Electrochim. Acta
, 49, 4021, 2004. With permission.)
[148]
inner or the surface structure of the BDD material is obviously altered by this treatment
and leads to faster electron transfers consequence.
Figure 4.27 presents Nyquist plots obtained at 0.37 V in a 0.5 × 10
-3
mol L
-1
ferrocene + 0.5 mol
L
-1
H
2
SO
4
aqueous solution for the BDD electrode after anodic and cathodic pretreatments.
The value of the high-frequency resistance element after the cathodic surface pretreatment is
also significant but not as in the case of the Fe(CN)
6
4-
/
3-
couple. The EIS experiments demon-
strate that a discontinuous passive layer or an internal transformation of the BDD will decrease
the surface blocking, which is caused by the cathodic pretreatment.
(a)
(b)
400
20
100 Hz
16
300
44.0 Hz
12
200
8
100
25 Hz
4
4.0 kHz
0
0
0
100
200
300
400
0
4
8
12
16
20
Z'
(Ω cm
2
)
Z'
(Ω cm
2
)
FIGURE 4.27
The Nyquist plots for the BDD electrode for a 0.5 × 10
-3
mol L
-1
ferrocene + 0.5 mol L
-1
H
2
SO
4
aqueous solu-
tion with measurements carried out at 0.37 V. (From Suffredini, H.B.,
Electrochim. Acta
, 49, 4021, 2004. With
permission.) [148]
