Use of the Simple Infiltrated Microstructure Polarization Loss Estimation (SIMPLE) model to describe the performance of nano-composite solid oxide fuel cell cathodes

Abstract

Nano-composite Sm(0.5)Sr(0.5)CoO(3-δ) (SSC)-Ce(0.9)Gd(0.1)O(1.95) (GDC) and La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) (LSCF)-GDC Solid Oxide Fuel Cell (SOFC) cathodes with various infiltrate loading levels were prepared through multiple nitrate solution infiltrations into porous GDC ionic conducting (IC) scaffolds. Microstructural analyses indicated that the average SSC and average LSCF hemispherical particle radii remained roughly constant, at 25 nm, across multiple infiltration-gelation-firing sequences. Comparisons between symmetric cell polarization resistance measurements and Simple Infiltrated Microstructure Polarization Loss Estimation (SIMPLE) model predictions showed that the SIMPLE model was able to predict the performance of heavily infiltrated SSC-GDC and LSCF-GDC cathodes with accuracies better than 55% and 70%, respectively (without the use of fitting parameters). Poor electronic conduction between mixed ionic electronic conducting (MIEC) infiltrate particles was found in lightly infiltrated cathodes. Since these electronic conduction losses were not accounted for by the SIMPLE model, larger discrepancies between the SIMPLE-model-predicted and measured polarization resistances were observed for lightly infiltrated cathodes. This work demonstrates that the SIMPLE model can be used to quickly determine the lowest possible polarization resistance of a variety of infiltrated MIEC on IC nano-composite cathodes (NCC's) when the NCC microstructure and an experimentally-applicable set of intrinsic MIEC oxygen surface resistances and IC bulk oxygen conductivities are known. Currently, this model is the only one capable of predicting the polarization resistance of heavily infiltrated MIEC on IC NCC's as a function of temperature, cathode thickness, nano-particle size, porosity, and composition.

The Effect of Precursor Solution Desiccation or Nano-Ceria Pre-Infiltration on Various La0.6Sr0.4FeyCo1-yO3-xInfiltrate Compositions

“…In all cases, measurements taken with AC amplitudes of 25 and 50 mV yielded identical impedance curve shapes, and the general shape of the impedance curves were consistent with those observed previously in the literature for LSF-LSC infiltrated ceria. 9,[13][14][15]20,21 For electrodes fabricated with a particular infiltration method, Figure 1 shows that the electrode resistance systematically decreases as the infiltrate Co:Fe ratio increases. This behavior is consistent with previous literature studies showing that at typical SOFC operating temperatures the oxygen surface exchange resistance (Rs) of materials within the LSC-LSF solid solution decrease as the Co:Fe ratio increases, 17,18,[22][23][24] and suggests that oxygen surface exchange is a dominant source of resistance in these cathodes at 600…”

“…Based on the definition of resistance, ohmic resistivity (ρ Ohmic ) values for each cell were determined by dividing the high-frequency Nyquist plot x-axis intercept by the electrolyte thickness and multiplying by the electrode's geometric area (0.5 cm 2 ). To help understand the observed performance trends, R P predictions were made using a previously-described 8,9,12 Simple Infiltrated Microstructure Polarization Loss Estimation (SIMPLE) model that accounts for electrical losses associated with oxygen exchange into the MIEC infiltrate and oxygen conduction through the GDC scaffold. Specifically, SIMPLE Model Rp predictions were made by inputting 1) La 0.6 Sr 0.4 Fe y Co 1-y O 3-x densities from the Joint Committee on Powder Diffraction Standards (JCPDS) database, 16 2) the MIEC infiltrate loading levels, cathode thicknesses, geometric cathode areas, cathode porosities, MIEC nano-particle diameters, and GDC scaffold column widths stated in Table I, 3) the GDC scaffold ionic conductivity from Nicholas et al, 9 4) the LSF, LSFC, and LSC oxygen surface exchange resistances (Rs) from Baumann et al, 17 5) the LSCF Rs from Xiong et al, 18 and 6) the LSCF55 Rs obtained by averaging the LSF and LSC Rs values from Baumann et al 17 into the SIMPLE model spreadsheet available at https://www.egr.msu.edu/nicholasgroup/simple.php.…”

Geometric Properties of Nanostructured Solid Oxide Fuel Cell Electrodes

“…For example, Shah et al 4 first reported that the infiltrated LSCF nanoparticles on the GDC backbone surface are hemispheres. Recently, Nicholas et al 13 reported that the infiltrated Sm 0.5 Sr 0.5 CoO 3-δ nanoparticles on the GDC backbone surface were also hemispherical. Fig.…”

“…5 neglects the resistance of backbone structure, while the recently proposed SIMPLE model by Nicholas et al considered it. 13 Thus the SIMPLE model is also used for validation. The reported parameters from the literature are used for model validation.…”

“…Since then, the TFV model has been widely used for simulating the infiltrated electrodes. Based on TFV model, Nicholas et al 13 modeled the infiltrated electrode structure as micrometer-scale columns coated with hemispherical nanoparticles, proposed the simple infiltrated microstructure polarization loss estimation (SIMPLE) model, and applied the SIMPLE model to predict the ASR of (Sm,Sr)CoO 3 infiltrated GDC electrodes and LSCF infiltrated GDC electrodes. These experimental studies and models (the random-packing approaches and the thinfilm approaches) successfully illustrate and confirm the importance of electrode microstructures.…”