3 The Measurements of the Oxygen Reduction Reaction
73
where k f (E) = k
0 exp{−a f
E − E
}, f = F/RT k0 is the standard rate constant
and α is the transfer coefficient. When there is no exact measurement, α is generally
considered to be equal to 0.5.
Substituting (3.66 into (3.67) gives:
i = F Ak f (E)C 0 (1 −
i
i d
)
(3.68)
Order i k = F Ak f (E)C 0 , you can get the Koutecký-Levich equation:
1
i
=
1
i k
+
1
i d
(3.69)
Where i k represents the current without any mass transfer, called the kinetic current;
i d is the limiting current; i is the measured current at any potential.
(3.69) can be transformed into:
i k =
i d × i
i d − i
(3.70)
By measuring the oxygen reduction polarization curve, we can obtain the
measured current i and the limit current i d , and substitute it into the above deformation
expression to obtain the kinetic current i k .
After the kinetic current i k is obtained, the i k is removed from the mass of the
catalyst platinum or its relative electrochemical specific surface area, and two key
parameters characterizing the activity of the oxygen reduction catalyst, mass activity
im and specific activity is further solved.
The measured current value at 0.9 V versus RHE is generally selected for dynamic
correction, and the kinetic current i k , mass activity i m and specific activity is calculated. The main reason is that if the important kinetic parameters of the exchange
current density are used for correction, since this parameter can only be obtained
by extrapolating the measured current, the extrapolation of the extrapolation method
causes a large error in the exchange current density, resulting in significant experimental error. In addition, if the activity standard is set at 0.9 V versus RHE, one can
guarantee the maximum output of power, because the fuel cell generally operates at
less than 0.9 V versus RHE; both can minimize the test error, which is Because at
lower potentials, the current is affected by Ohmic drop and oxygen mass transfer,
while at higher potentials, the test on the rotating ring disk electrode is affected by
the electric double layer, and the fuel cell stack is infiltrated by hydrogen influences.
Moreover, the simulation test results of the rotating disk electrode at 0.9 V versus
RHE have a high degree of fit with the actual test results of the fuel cell. H. A.
Gasteiger et al. reported that the oxygen reduction activity on the rotating disk electrode of the Pt/C catalyst at 0.9 V versus RHE was consistent with that measured by
73
where k f (E) = k
0 exp{−a f
E − E
}, f = F/RT k0 is the standard rate constant
and α is the transfer coefficient. When there is no exact measurement, α is generally
considered to be equal to 0.5.
Substituting (3.66 into (3.67) gives:
i = F Ak f (E)C 0 (1 −
i
i d
)
(3.68)
Order i k = F Ak f (E)C 0 , you can get the Koutecký-Levich equation:
1
i
=
1
i k
+
1
i d
(3.69)
Where i k represents the current without any mass transfer, called the kinetic current;
i d is the limiting current; i is the measured current at any potential.
(3.69) can be transformed into:
i k =
i d × i
i d − i
(3.70)
By measuring the oxygen reduction polarization curve, we can obtain the
measured current i and the limit current i d , and substitute it into the above deformation
expression to obtain the kinetic current i k .
After the kinetic current i k is obtained, the i k is removed from the mass of the
catalyst platinum or its relative electrochemical specific surface area, and two key
parameters characterizing the activity of the oxygen reduction catalyst, mass activity
im and specific activity is further solved.
The measured current value at 0.9 V versus RHE is generally selected for dynamic
correction, and the kinetic current i k , mass activity i m and specific activity is calculated. The main reason is that if the important kinetic parameters of the exchange
current density are used for correction, since this parameter can only be obtained
by extrapolating the measured current, the extrapolation of the extrapolation method
causes a large error in the exchange current density, resulting in significant experimental error. In addition, if the activity standard is set at 0.9 V versus RHE, one can
guarantee the maximum output of power, because the fuel cell generally operates at
less than 0.9 V versus RHE; both can minimize the test error, which is Because at
lower potentials, the current is affected by Ohmic drop and oxygen mass transfer,
while at higher potentials, the test on the rotating ring disk electrode is affected by
the electric double layer, and the fuel cell stack is infiltrated by hydrogen influences.
Moreover, the simulation test results of the rotating disk electrode at 0.9 V versus
RHE have a high degree of fit with the actual test results of the fuel cell. H. A.
Gasteiger et al. reported that the oxygen reduction activity on the rotating disk electrode of the Pt/C catalyst at 0.9 V versus RHE was consistent with that measured by