Diffusion and Gas Conversion Analysis of Solid Oxide Fuel Cells at Loads via AC Impedance

Table 2

Fitted equivalent circuit elements using the circuit model as shown in Figure 6, varying anode fuel feeds for three individual cells in a five-cell stack, and operating at 800°C, 52.46 mA cm⁻². Feeds were 38.5 ~ 97.0% H₂, 3.0% H₂O, and balance N₂.

Physical elements	𝑥𝐻 (Cell 1)			𝑥𝐻 (Cell 3)			𝑥𝐻 (Cell 5)
	38.5%	64.6%	97.0%	38.5%	64.6%	97.0%	38.5%	64.6%	97.0%
𝑅Ω (mΩ cm^2)	1316	1287	1261	673.4	661.9	657.6	805.2	792.4	792.4
𝑅^𝜃ct (mΩ cm^2)	300.2	256.2	244.9	287.6	235.0	220.5	226.5	189.5	178.2
𝐶^𝑐𝑑 (mF cm^−2)	11.50	15.13	13.56	11.80	12.16	14.07	10.28	10.81	11.42
𝑅^𝑎ct (mΩ cm^2)	148.8	174.8	181.4	115.8	116.6	141.9	81.62	87.78	97.23
𝐶^𝑎𝑑 (mF cm^−2)	5.646	5.089	4.673	6.564	6.448	5.789	6.308	5.730	5.815
𝑅^𝑎𝜃 (mΩ cm^2)^†	−118.0	−69.17	−39.12	−78.32	−74.42	−60.45	−68.44	−74.60	−61.67
𝐶^𝑎𝜃 (F cm^−2)^†	−1.984	−3.739	−5.705	−1.481	−2.356	−2.726	−1.277	−1.455	−2.449
Y0 (S cm^−2 s^1/2)	1.204	1.599	2.051	1.292	1.554	1.857	1.351	1.595	1.907
B (s^1/2)	1.445	1.543	1.668	1.313	1.394	1.467	1.337	1.383	1.457
χ ^2 (*10^−6)^‡	63.7	44.3	26.9	171	97.8	90.4	182	126	76.4

^†Negative values of 𝑅_𝜃 and 𝐶_𝜃 indicate that the inductive behavior of anode adsorbed intermediates is more significant than the capacitive portion. The same fits can be obtained without negative values, when the parallel 𝑅_𝜃-𝐶_𝜃 is replaced with a series R_L-L moved in parallel with the anode 𝑅^𝑎_ct [21].
^‡χ ² is the nonlinear least squares residual.