Effect of Firing Temperature on LSM-YSZ Composite Cathodes: A Combined Three-Dimensional Microstructure and Impedance Spectroscopy Study

Cronin, J. Scott; Muangnapoh, Kullachate; Patterson, Zach; Yakal-Kremski, Kyle; Dravid, Vinayak P.; Barnett, Scott A.

doi:10.1149/2.053204jes

Cited by 67 publications

(40 citation statements)

References 41 publications

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“…These show the substantial decrease in polarization resistance (R P ) during break in, with the cell becoming quite stable after ∼100 h. The form of the impedance response is similar to that reported previously for LSM- YSZ electrodes. 15 In summary, LSM-YSZ electrodes are stable under current switching up to low current densities, at least over a time frame of a few hundred hours. Figure 5 summarizes the EIS-derived R and R P data versus time for six cells operated with current switching at 1.5 Acm −2 .…”

Section: Resultsmentioning

confidence: 93%

Durability Testing of Solid Oxide Cell Electrodes with Current Switching

Hughes

Yakal-Kremski

Call

et al. 2012

J. Electrochem. Soc.

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A method for durability testing of solid oxide cell electrodes in current-switching operation is presented. The aim is to obtain correlated time-dependent electrochemical and microstructural information by simultaneously testing multiple identical cells connected in series. By periodically removing cells from the circuit during the life test, microstructural changes were observed after different times under current using Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) tomography. Initial tests were done on symmetrical cells with (La 0.8 Sr 0.2 ) 0.98 MnO 3 -Zr 0.84 Y 0.16 O 2 (LSM-YSZ) electrodes at 800 • C in air with a current of up to 1.5 Acm −2 . The current direction was switched every 30 minutes. Electrochemical Impedance Spectroscopy (EIS) measurements showed stable operation at low currents, but a gradual degradation of both ohmic and polarization resistance at 1.5 Acm −2 . Little microstructural change was observed except that silver from current collectors was found to migrate into the electrodes near the YSZ electrolyte during fuel cell operation. The silver content increased with time at current and presumably explained the observed increase in polarization resistance.Life testing of solid oxide cells (SOCs) presents significant challenges, not only because of long desired operation times (>40,000 h) but because of the materials complexity of SOCs. There are a number of examples of SOC stack tests carried out for >10,000 h, and they invariably show that a number of factors contribute to degradation. 1,2 A different strategy is to carry out tests focused on a specific cell component, using conditions that accelerate degradation such that a large amount of data can be obtained in a relatively short time. When the electrochemical measurements are correlated with microstructural and microchemical measurements, they can provide a more fundamental understanding of specific degradation mechanisms and ultimately lead to mechanistic degradation models that can be used to make quantitative long-term durability predictions. 3 One problem with such measurements is that artifacts, such as impurity accumulation, 4 can obfuscate the observation of the intrinsic degradation mechanism.The specific application addressed here is a SOC alternated between fuel cell and electrolysis operation, of interest for storing excess electrical energy from intermittent renewable sources such as wind and solar, and then converted back to electricity. 5 Prior work has focused on observing degradation mechanisms in SOCs operated in either fuel cell 6,7 or electrolyzer 8-10 mode. The ability of SOCs to work reliably over many cycles of switched current direction, i.e., between fuel cell and electrolysis modes, is unknown. This paper describes a novel method for coupled electrochemical and microstructural life testing, applied to air:LSM-YSZ | YSZ | LSM-YSZ:air symmetrical SOCs in current-switching operation. These tests allowed a more straightforward interpretation of EIS data compared to full cells, especially since the current...

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Section: Resultsmentioning

confidence: 93%

Durability Testing of Solid Oxide Cell Electrodes with Current Switching

Hughes

Yakal-Kremski

Call

et al. 2012

J. Electrochem. Soc.

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“…In this study, we show that the EIS data of a SOFC MIEC cathode can be used to determine the tortuosity of the solid phase within the cathode. In particular, we consider a statistically representative ( Scott Cronin et al, 2012 ) portion of an experimentally determined complex three-dimensional microstructure of an unbiased SOFC cathode. In the microstructure, we solve for the amplitude of the concentration-response to an applied AC load under the influence of surface reaction and bulk diffusion, and subsequently, use the solution to determine the impedance behavior.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the Electrochemical Impedance in a Three-Dimensional, Complex Microstructure of Solid Oxide Fuel Cell Cathode and Its Application in the Microstructure Characterization

et al. 2021

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Electrochemical impedance spectroscopy (EIS) is a powerful technique for material characterization and diagnosis of the solid oxide fuel cells (SOFC) as it enables separation of different phenomena such as bulk diffusion and surface reaction that occur simultaneously in the SOFC. In this work, we simulate the electrochemical impedance in an experimentally determined, three-dimensional (3D) microstructure of a mixed ion-electron conducting (MIEC) SOFC cathode. We determine the impedance response by solving the mass conservation equation in the cathode under the conditions of an AC load across the cathode’s thickness and surface reaction at the pore/solid interface. Our simulation results reveal a need for modifying the Adler-Lane-Steele model, which is widely used for fitting the impedance behavior of a MIEC cathode, to account for the difference in the oscillation amplitudes of the oxygen vacancy concentration at the pore/solid interface and within the solid bulk. Moreover, our results demonstrate that the effective tortuosity is dependent on the frequency of the applied AC load as well as the material properties, and thus the prevalent practice of treating tortuosity as a constant for a given cathode should be revised. Finally, we propose a method of determining the aforementioned dependence of tortuosity on material properties and frequency by using the EIS data.

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“…The determination of important properties like tortuosity and triple phase boundary (TPB) length in the porous SOFC cathode and anode requires reconstruction of the three-dimensional (3D) microstructure. An established technique for this purpose is focused ion beam (FIB)-SEM serial sectioning tomography, which allows to reconstruct the 3D microstructure with a spatial resolution in the few 10 nm range and extract performance-relevant cell parameters [2][3][4][5][6][7]. In FIB-SEM tomography, a series of alternating FIB milling and SEM imaging steps produces a set of images through a chosen sample volume.…”

Section: Introductionmentioning

confidence: 99%

“…However, some commonly used SOFC materials exhibit weak material contrast because their average atomic numbers are similar. This applies, e.g., to (La,Sr)MnO 3 (LSM) and Y 2 O 3 -doped ZrO 2 , (YDZ), which are commonly used in SOFC cathodes [4,5,[8][9][10]. In some instances, SE SEM imaging at low electron energies (0.6-2 keV) and employing an in-lens SE detector have also been successful to generate material contrast in SOFC anodes or cathodes [4,6,[11][12][13][14], because SE coefficients increase with decreasing electron energy and the effect of the work function of the material influences SE emission [12,15].…”

Section: Introductionmentioning

confidence: 99%

Optimization of Material Contrast for Efficient FIB‐SEM Tomography of Solid Oxide Fuel Cells

et al. 2020

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Focused ion beam (FIB)-scanning electron microscopy (SEM) serial sectioning tomography has become an important tool for three-dimensional microstructure reconstruction of solid oxide fuel cells (SOFC) to obtain an understanding of fabrication-related effects and SOFC performance. By sequential FIB milling and SEM imaging a stack of cross-section images across all functional SOFC layers was generated covering a large volume of 3.5Á10 4 μm 3. One crucial step is image segmentation where regions with different image intensities are assigned to different material phases within the SOFC. To analyze all relevant SOFC materials, it was up to now mandatory to acquire several images by scanning the same region with different imaging parameters because sufficient material contrast could otherwise not be achieved. In this work we obtained high-contast SEM images from a single scan to reconstract all functional SOFC layers consisting of a Ni/Y 2 O 3-doped ZrO 2 (YDZ) cermet anode, YDZ electrolyte and (La,Sr)MnO 3 /YDZ cathode. This was possible by using different, simultaneous read-out detectors installed in a stateof-the-art scanning electron microscope. In addition, we used a deterministic approach for the optimization of imaging parameters by employing Monte Carlo simulations rather than trial-and-error tests. We also studied the effect of detection geometry, detecting angle range and detector type.

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Effect of Firing Temperature on LSM-YSZ Composite Cathodes: A Combined Three-Dimensional Microstructure and Impedance Spectroscopy Study

Cited by 67 publications

References 41 publications

Durability Testing of Solid Oxide Cell Electrodes with Current Switching

Durability Testing of Solid Oxide Cell Electrodes with Current Switching

Simulation of the Electrochemical Impedance in a Three-Dimensional, Complex Microstructure of Solid Oxide Fuel Cell Cathode and Its Application in the Microstructure Characterization

Optimization of Material Contrast for Efficient FIB‐SEM Tomography of Solid Oxide Fuel Cells

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