Chemistry Reference
In-Depth Information
•
for
t
=
0
and
x
≥
0
c
=
c
for
t
≥
0
and
x
Æ
0
c
Æ
c
•
for
t
>
0
and
x
=
0
c
=
0
it is possible to calculate that the variation of the concentration of elec-
troactive material as a function of time at the surface of the electrode:
d
d
c
x
c
•
Ê
Ë
ˆ
¯
=
[1.48]
12
12 12
p
D
t
(
)
0
,t
and the flux of material crossing the boundary of the electrode is obtained
by the following equation:
InA
c
d
(
)
0,
t
=
FD
[1.49]
d
x
The concentration-distance profiles predicted by Equation 1.48 and result-
ing in the current in Equation 1.49 are given in Fig. 1.13. A complete expres-
sion for the current that results from semi-infinite diffusion is obtained as
follows, which in fact is also called the Cotrell equation for a planar
electrode:
nA
t
FD
12
12 12
•
[1.50]
I
=
c
p
x
1.13
Concentration profile of the analyte in the vicinity of the elec-
trode and concentration gradient variation as a function of pro-
ceeding electrochemical reaction.
