Theoretical Verification Necessity of Leakage Currents Using Sm Doped Ceria Electrolytes in SOFCs~!2009-01-29~!2009-03-03~!2009-03-19~!

Abstract

Numerous approaches have been made to solve the basic transport equation that describes a solid oxide fuel cell (SOFC) with mixed conduction. Classically, the open circuit voltage (OCV) is calculated with Wagner's equation, which is right within the limits of linear transport theory. In order to generalize Wagner's equation, many models have been proposed to describe the current-voltage relation in mixed ionic electronic solid conductors (MIEC) using constant field approximation to calculate an electronic current. However, experimental verification necessity of leakage currents in SOFCs using Sm doped Ceria electrolytes has already been pointed out both qualitatively and in quantities. Using the constant field approximation, the limits of linear transport theory can not be clear. In this report, a new model is expressed without using the constant field approximation. This model follows from Wagner's equation and continuity. The calculated electronic current for doped Ceria electrolyte matches the values calculated using conventional models. But the electrical field near the cathode is large enough to cause dielectric breakdown which has never been reported. Continuity is not deniable, so there are limitations in Wagner's equation, coming from the limits of linear transport theory.

Performance of Newly Developed Co Doped Sm0.95Ce0.05FeO3-δ as SOFC Anode Material

“…However, SDC has consistently shown OCV values lower than expected. This observation has been explained in the literature in terms of SDC's low densification (16) and its partial reduction near the surface of the anode (17,18) under fuel conditions. Additionally, the difference between the theoretical and experimental OCV values is consistently temperature dependent, suggesting that it is an intrinsic property of the system and not a function of the setup.…”

Performance of Sm0.95Ce0.05Fe1-xNixO3-δPerovskite as Anode Materials under Methane Fuel for Low Temperature Solid Oxide Fuel Cells (LT -SOFC)

“…The measured OCV values under hydrogen were lower than the theoretical Nernst potential values. As an example the theoretical Nernst potential values at 700 o C and 450 o C are 1.03 V and 1.089 V, respectively, but the experimental values were 0.88 V (at 700 o C) and 1.0 V (at 450 o C).This observation of lower OCV values using a SDC electrolyte has been previously linked to its lower densification (12), and its partial reduction near the surface of anodes under fuel cell conditions (13,14). The results of AC impedance analysis under hydrogen fuel are shown in Figure 2.…”

Doped Samarium Ferrite Perovskites as Carbon and Sulfur Resistant Anodes for Low Temperature Solid Oxide Fuel Cells

“…However, at high temperature we observe a characteristic lowering of the OCV value (0.86 measured vs. 1.03V expected at 700°C). This observation is common for SDC electrolytes and has been explained in terms of low densification and partial reduction near the surface of the anode (24)(25)(26)(27).…”