74
C. Juhong et al.
the fuel cell stack, while at 0.8 V versus RHE there was a bias. Therefore, in combination with various factors, most literature and fuel cell activity standards use 0.9 V
versus RHE as the dynamic correction standard and activity comparison standard.
From the above derivation process and the Levich limit current equation, the
factors affecting the limit current value include the number of electrons involved in
the electrode reaction, the electrode area, the angular velocity of the electrode, the
dynamic viscosity of the electrolyte solution, and the diffusion ability and solubility
of oxygen molecules. From the current measurement of the limit current in most
of the literature, the limit current measured at 1600 rpm for different catalysts is
6 mA.cm
−2 at 298 K, which also proves that for the speed, temperature, electrolyte
type and the oxygen reduction test system of the same concentration has a constant
current value as long as the catalyst layer is sufficiently uniform and the thickness is
moderate, regardless of the type of the catalyst and the grain size.
If i d → 6 mA.cm
−2 , L Pt = 20 μg.cm
−2 , the relationship between i and i m can be
obtained.
i m (A mg
−1
Pt ) →
3i(mA cm
−2
)
60 − 10i(mA cm
−2
)
(3.71)
The graph of Fig. 3.21 can be obtained by plotting the above formula. When the
measured current i at 0.9 V infinitely approaches the limiting current of 6 mA.cm
−2 ,
the mass activity i m increases rapidly.
The mass activity of the catalyst released by the U.S. Department of Energy at 0.9
V iR-free versus RHE will reach 0.44A.mg Pt
−1 by 2017. Although most of the current
research is focused on improving oxygen reduction activity, there are still many
problems to be solved. If only from the point of view of mass activity calculation
and oxygen reduction curve analysis, the method of increasing oxygen reduction
activity is to increase the measured current of 0.9 V iR-free versus RHE while ensuring
Fig. 3.21 The relationship
between i m and i. i d →
6 mA.cm −2 , L Pt =
20 μg.cm −2
1
2
3
4
5
6
0
2
4
6
8
10
12
i
m / A mg
-1
Pt
i 0.9V, iR-free / mA cm
-2
C. Juhong et al.
the fuel cell stack, while at 0.8 V versus RHE there was a bias. Therefore, in combination with various factors, most literature and fuel cell activity standards use 0.9 V
versus RHE as the dynamic correction standard and activity comparison standard.
From the above derivation process and the Levich limit current equation, the
factors affecting the limit current value include the number of electrons involved in
the electrode reaction, the electrode area, the angular velocity of the electrode, the
dynamic viscosity of the electrolyte solution, and the diffusion ability and solubility
of oxygen molecules. From the current measurement of the limit current in most
of the literature, the limit current measured at 1600 rpm for different catalysts is
6 mA.cm
−2 at 298 K, which also proves that for the speed, temperature, electrolyte
type and the oxygen reduction test system of the same concentration has a constant
current value as long as the catalyst layer is sufficiently uniform and the thickness is
moderate, regardless of the type of the catalyst and the grain size.
If i d → 6 mA.cm
−2 , L Pt = 20 μg.cm
−2 , the relationship between i and i m can be
obtained.
i m (A mg
−1
Pt ) →
3i(mA cm
−2
)
60 − 10i(mA cm
−2
)
(3.71)
The graph of Fig. 3.21 can be obtained by plotting the above formula. When the
measured current i at 0.9 V infinitely approaches the limiting current of 6 mA.cm
−2 ,
the mass activity i m increases rapidly.
The mass activity of the catalyst released by the U.S. Department of Energy at 0.9
V iR-free versus RHE will reach 0.44A.mg Pt
−1 by 2017. Although most of the current
research is focused on improving oxygen reduction activity, there are still many
problems to be solved. If only from the point of view of mass activity calculation
and oxygen reduction curve analysis, the method of increasing oxygen reduction
activity is to increase the measured current of 0.9 V iR-free versus RHE while ensuring
Fig. 3.21 The relationship
between i m and i. i d →
6 mA.cm −2 , L Pt =
20 μg.cm −2
1
2
3
4
5
6
0
2
4
6
8
10
12
i
m / A mg
-1
Pt
i 0.9V, iR-free / mA cm
-2