Uncertainty Quantification in SOFC Modeling
The cathode reaction in solid oxide fuel cells is complex and still not completely
understood. The most popular SOFC cathode is strontium-doped lanthanum manganate
(LSM), which is a conductor of both electrons and oxygen ions. The oxygen conductivity
in LSM is very poor, however, its performance as a cathode material is much better
than metals like platinum, where oxygen incorporation reactions are limited to
the triple phase boundary (TPB) between the air, the electrode and the electrolyte.
This suggests that there is some transport of oxygen in LSM, which extends the
incorporation reaction to the surface of the electrode. Patterned electrode experiments
have been used to quantify the extent of electrode surface that is active, but
these are not produced in the same manner as the porous materials that typically
serve as SOFC electrodes.
In collaboration with the National Energy Technology Laboratory’s Solid Oxide
Fuel Cell program, Bayesian calibration was used to quantify an impedance model
for a porous LSM SOFC cathode, generating an estimate of the effective width of
the active region (in other words, the extent to which the reduction reaction takes
place on the LSM surface away from the TPB) and quantifying model parameters. Microstructural
data gathered using X-ray Computed Tomography (Carnegie Mellon) was used to specify
critical geometric parameters such as the length of the TPB and the total LSM surface
area per unit area of the electrolyte, thus replicating the kind of detailed geometric
information available in patterned electrodes. Preliminary results show that a
majority of the current moves through the TPB, but a significant minority takes
a route through the bulk of LSM within nanometers of the electrolyte.