Online Simple Infiltrated Microstructure Polarization Loss Estimation (SIMPLE) Model Nano-Composite Solid Oxide Fuel Cell Cathode Polarization Resistance Calculator
Remember, 0.1 Ohm*cm2 is needed for practical device operation.
SIMPLE Model Publications
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Nicholas JD, Wang L, Call AV, Barnett SA. Use of the Simple Infiltrated Microstructure Polarization Loss Estimation (SIMPLE) Model to Describe the Performance of Nano-Composite Solid Oxide Fuel Cell Cathodes. Physical Chemistry Chemical Physics 2012; 14: 15379-15392.
http://dx.doi.org/10.1039/C2CP43370B |
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Nicholas JD, Barnett SA. Measurements and Modeling of Sm0.5Sr0.5CoO3-x — Ce0.9Gd0.1O1.95 SOFC Cathodes Produced Using Infiltrate Solution Additives. Journal of the Electrochemical Society 2010; 157: B536
http://dx.doi.org/10.1149/1.3284519 |
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Shah M, Nicholas JD, Barnett SA. Prediction of Infiltrated Solid Oxide Fuel Cell Cathode Polarization Resistance Using Simple Models. Electrochemistry Communications 2008; 11: 2.
http://dx.doi.org/10.1016/j.elecom.2008.10.006 |
SIMPLE Model Overview
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As discussed in Nicholas et al. Phys. Chem. Chem. Phys. 2012, because of its analytical form the SIMPLE model provides a quick and easy means of determining the lowest possible open-circuit polarization resistance, RP, of Mixed Ionic Electronic Conductor (MIEC) on Ionic Conductor (IC) composite Solid Oxide Fuel Cell (SOFC) cathodes when:
1) bulk oxygen transport mainly occurs through the ionic conducting scaffold, &
2) oxygen ion incorporation mainly occurs on the MIEC particle surfaces.
These requirements are commonly met for nano-composite cathodes (NCC´s) made via the infiltration of a range of MIECs (La0.6Sr0.4Co0.8Fe0.2O3-x, Sm0.5Sr0.5CoO3-x, other cobaltite oxygen surface exchange catalysts, etc.) into a range of ionic conducting scaffolds (ceria, zirconia, lanthanum strontium gallium manganite, etc.). Therefore, the SIMPLE model can be used as a SOFC NCC´s design tool, as illustrated in the SIMPLE Model Calculator (above), and in this: |
SIMPLE Model Assumptions
As discussed in
As discussed in Nicholas et al. Phys. Chem. Chem. Phys. 2012, the SIMPLE model makes a series of assumptions about SOFC NCC geometries and materials properties.
| ASSUMPTION | JUSTIFICATION |
| The only significant resistances are MIEC oxygen surface exchange resistance and IC scaffold bulk oxygen transport |
This is a good approximation for heavily-infiltrated NCC´s (i.e. those with percolated infiltrate particles; percolation typically occurs when the infiltrate particles cover at least 44% of the scaffold surface) being tested at open circuit. Electronic conduction losses can be a significant significant source of resistance in lightly-infiltrated NCC´s. Other sources of resistance are insiginificant for most NCC materials combinations at open circuit. See Nicholas et al. Energy and Environmental Science, Submitted (2012), for details. Violation of this assumption will not prevent the SIMPLE model from predicting the lowest-possible NCC open-circuit RP. |
| Oxygen transport through the IC scaffold behaves ohmically. | This is another way of saying that the ionic conductor behaves as a dilute, ideal solution with a constant composition and structure throughout. The low currents and overpotentials used in symmetric cell, open circuit, cathode polarization resistance tests (which are conducted in the absence of a pO2 gradient) make this a reasonable assumption. |
| Oxygen transport across the MIEC surface behaves ohmically. | This is a good assumption for symmetric cells tested at open-circuit because more-complicated models (the Butler-Volmer Equation, etc.) predict ohmic surface exchange behavior at low overpotentials. |
| The IC scaffold can be approximated as a series of high aspect ratio columns. | This is a good assumption as long as the IC particle size is much less than the cathode thickness, the IC scaffold particles are well necked, and the surface resistance losses are on the same order of magnitude (or greater than) bulk conduction losses. Typical NCC microstructures and materials properties make this a reasonable assumption. |
| Infiltrate instrinsic surface resistances are identical to those of thin-film micro-electrodes tested under identical conditions. |
This assumption is a necessary evil until the SOFC community obtains intrinsic surface resistance measurements on infiltrate nano-particles. The generally close agreement between the measured and SIMPLE-model-predicted RP's suggest this is a reasonable assumption. |
| If not directly measured, the MIEC surface area can be accurately estimated by assuming the MIEC infiltrate particles are hemi-spherical in shape. | Typical NCC microstructures make this a reasonable assumption. |
These assumptions are discussed more fully in
Nicholas et al. Phys. Chem. Chem. Phys. 2012, and in this:
