Diffusion and Gas Conversion Analysis of Solid Oxide Fuel Cells at Loads via AC Impedance
Table 1
Values for a parallel RC as shown in Figure 5(a) are fitted to the low-frequency impedance loops of button cells.
(a) Varying hydrogen feed concentration at two temperatures
Physical elements
B
B
*
Note
xH (T = 750°C)
(mΩ cm2)
(F cm−2)
(S cm−2 s1/2)
(s1/2)
(S cm−2 s1/2)
(s1/2)
47.3%
138.5
40.60
25.66
4.493
25.71
4.493
i = 175 mA cm−2
63.7%
137.4
41.40
26.13
4.412
26.42
4.435
97.0%
120.1
51.85
31.25
4.700
31.43
4.713
xH (T = 800°C)
33.1%
172.3
58.45
26.76
5.441
27.53
5.532
i = 175 mA cm−2
45.5%
146.9
78.55
35.56
6.090
33.32
5.831
97.0%
123.6
88.35
37.98
5.643
40.64
5.079
*The finite diffusion element (FDE), fitted in series with the Faradaic impedance as shown in Figure 5(b), is also listed in this Table 1(a), showing little difference between the parallel RC and the series fits.
(b) Varied load current density at two hydrogen feed concentrations