eDAQ Picostat, Руководство пользователя

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112 eDAQ Potentiostats
Chronocoulometry
The Integrated Cottrell Equation
The current response equation at a planar electrode for a
chronocoulometric experiment is the time integrated form of the Cottrell
equation:
where
Q = the number coulombs transferred
n = the number of electrons transferred to (or from) the substrate
molecule
A = area of the exposed surface of the electrode (cm
2
)
D = diffusion coefficient of the substrate molecule (cm
2
/s).
C = concentration of the substrate molecule (mol/L)
t = time (s)
k = a constant.
Thus a plot of Q versus t
1/2
should produce a straight line with an
intercept of k , which in turn can be defined as:
k = nFA Γ + Q
dl
where
Γ = surface concentration of adsorbed substrate (mol/cm
2
)
Q
dl
= double layer charging.
Q
i t
d
0
t
∫
2 nFAD
1 2
⁄
Ct
1 2
⁄
1000
π
1 2
⁄
-----------------------------------------
k
+ = =