No abstract

Nanocomposite Sm 0.5 Sr 0.5 CoO 3−x ͑SSC͒-Ce 0.9 Gd 0.1 O 1.95 ͑GDC͒ solid oxide fuel cell ͑SOFC͒ cathodes were produced by infiltrating SSC nitrate solutions into GDC scaffolds. A single infiltration of a concentrated solution resulted in a low polarization resistance of 0.1 ⍀ cm 2 at 600°C. Infiltrate solution additives slightly improved the SSC phase purity but did not significantly alter the SSC particle morphology/size or the infiltrated cathode polarization resistance. Polarization resistance predictions made using microstructural observations and a simple model were found to be within 35% of the experimentally measured values without the use of fitting parameters.Many different solid oxide fuel cell ͑SOFC͒ cathodes have been produced by infiltrating a mixed ionic and electronic conducting ͑MIEC͒ phase, typically, a Co-or Fe-based perovskite, into an ionically conducting scaffold, typically, doped ceria or zirconia. 1-15 In many cases, these cathodes have exhibited a polarization resistance R P lower than powder-processed composites of the same materials. In particular, a useful R P value of 0.1 ⍀ cm 2 was achieved at the quite low temperature of 550°C for Sm 0.5 Sr 0.5 CoO 3−x ͑SSC͒-Ce 0.8 Sm 0.2 O 1.9 ͑SDC͒ cathodes produced via multiple SSC infiltrations. 15 Qualitatively, this low R P value can be attributed to the high SSC surface area in the infiltrated cathode, the high SSC oxygen surface exchange coefficient, 16 and the high SDC oxygen ion conductivity. 17 Until recently, a quantitative understanding of MIEC infiltrated cathodes has been lacking in two areas. First, multication oxides produced via nitrate solution infiltration often lack phase purity, 1,12 and it is not known how the impurity phases impact cathode performance. Second, existing composite cathode models ͑which utilize simplified particle geometries 18-23 or finite element/difference mesh calculations 24 ͒ were developed for micrometer-sized, powderprocessed composites. Recently, these models have been extended/ modified to handle infiltrated nanocomposite cathodes. 25,26 However, the experimental validation of these newly developed infiltrated cathode models ͑especially over a range of temperatures, microstructures, and material combinations͒ remains incomplete.Therefore, the first aim of the present paper was to determine if infiltrate solution additives, specifically the surfactant Triton X-100 or the chelating agent deprotonated citric acid, could affect the infiltrated SSC nanoparticle morphology and/or phase purity. The second aim was to determine if the polarization resistance of SSC infiltrated GDC cathodes agreed with predictions from the infiltrated cathode model developed in Ref. 26. ExperimentalTo evaluate the effects of the precursor solution additives, a pure 0.50 M nitrate solution, a Triton X-100 containing 0.50 M nitrate solution, and a deprotonated citric acid containing 0.50 M nitrate solution were prepared. The pure nitrate solution was prepared by dissolving the appropriate amount of samarium nitrate hydrate ͑Alfa ...

Long-range charge transfer leads to oxygen vacancy interactions in strontium ferrites.

No 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.