The equation developed in class was: V = Eoc - Aln (+n) - ir - meni. Neglecting in, we can rewrite it as: Ve = Eoc + Alni - ir - meni.
Combining the first two terms on the right as Eoc (if io is small, ln(io) is negative, so Eoc < E), we can write: Ve = Eoc - Alni - ir - meni.
a. Use this expression and the data in the following table to plot (using a computer) two polarization curves, one for a low-temperature PEMFC operating at 70°C, and the other for a high-temperature SOFC. Use the range 1 < i < 1100 mA/cm for your plot. Plot both curves on the same graph to allow a direct comparison.
b. Also on the same graph, plot the power curves for both fuel cells. If you express the power in W/cm^2, then all four curves will scale nicely on the same graph.
c. Explain, using one or two sentences each, the relative values of each of the five constants for the two types of FCs. For example, explain why A is larger for PEMFCs compared to SOFCs and so on.
Constant
PEMFC at 70°C
High-Temperature SOFC
Eoc (V)
1.031
1.01
r (k cm^2)
2.45E-4
2.0E-4
A (V)
0.03
0.002
m (V)
2.11E-5
8E-3
n (cm^2 mA^-1)
1.0E-4
8E-3