Firing Temperature Effect on 3D Microstructure and Performance of LSM-YSZ Composite SOFC Cathodes

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

doi:10.1149/1.3570233

Cited by 5 publications

(3 citation statements)

References 25 publications

(48 reference statements)

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“…Table 2 summarizes the characteristics of the two responses. Neither electrode showed evidence of significant gas phase diffusion concentration polarization down to the lowest pressure studied here, pO 2 = 0.1 atm; this is reasonable given the relatively thin electrode and current collector layers, and the relatively high porosity of ~ 50 vol% (16,17,21,22). The LSM-YSZ composite electrode displayed overlapping responses, one at 10 3 Hz and another at 10 -100 Hz.…”

Section: Discussionsupporting

confidence: 53%

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Electrochemical Performance of Solid Oxide Cell Oxygen Electrodes Under Pressurization

Hughes¹,

Railsback²,

Butts³

et al. 2015

ECS Trans.

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The solid oxide cell (SOC) composite oxygen electrodes (La 0.8 Sr 0.2 ) 0.98 MnO 3-δ -Zr 0.84 Y 0.16 O 2-γ (LSM-YSZ) and La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3-δ (LSCF) -Ce 0.8 Gd 0.2 O 1.95 (LSCF-GDC) were studied at oxygen partial pressure pO 2 from 0.1 to 10 atm by impedance spectroscopy. Both electrodes showed a main response at frequency < 100 Hz that decreased in size and frequency with increasing pO 2 , and a smaller response at ~ 10 3 Hz. The impedance spectra were fit using an equivalent circuit model with two RQ elements. Total electrode resistances decreased with increasing pO 2 following a pO 2 -0.17 dependence for LSM-YSZ and a pO 2 -0.20 dependence for LSCF-GDC. Overall, the area-specific resistance of these oxygen electrodes is reduced by a factor of ~2 by increasing oxygen pressure from a nominal 0.2 atm (air) to 10 atm, thereby improving SOC performance.

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Section: Discussionsupporting

confidence: 53%

“…The LSM layers were fired at 1075°C for 1 hour, and the LSCF layers were fired at 1100°C for 1 hour, leaving a current collector layer of ~ 20 µm. The electrode porosity was ~ 50 vol%, based on previous microstructural characterization of similarly processed electrodes (16)(17)(18)(19).…”

Section: Methodsmentioning

confidence: 99%

Electrochemical Performance of Solid Oxide Cell Oxygen Electrodes Under Pressurization

Hughes¹,

Railsback²,

Butts³

et al. 2015

ECS Trans.

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“…Multiple series-connected cells started the life tests, but as they proceeded cells were removed from the circuit periodically, allowing observation of the microstructure after different numbers of current-switching cycles. Three-dimensional FIB-SEM tomography 11 and SEM-EDS were utilized to quantify microstructural and microchemical changes. The role of the Ag current collectors used in the test and the observed Ag accumulation in the electrode active region are discussed.…”

mentioning

confidence: 99%

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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Studies of Solid Oxide Fuel Cell Electrode Evolution Using 3D Tomography

et al. 2013

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This paper describes 3D tomographic investigations of the structural evolution of Ni‐yttria‐stabilized zirconia (Ni‐YSZ) and (La,Sr)MnO3‐YSZ (LSM‐YSZ) composite solid oxide fuel cell (SOFC) electrodes. Temperatures higher than normally used in SOFC operation are utilized to accelerate electrode evolution. Quantitative 3D FIB‐SEM and X‐ray tomographic imaging contributes to development of mechanistic evolution models needed to accurately predict long‐term durability. Ni‐YSZ anode functional layers annealed in humidified hydrogen at 900–1,100 °C exhibited microstructural coarsening leading to a decrease in three‐phase boundary (TPB) density. There was also a change in the fraction of pores that were isolated, which impacted the density of electrochemically active TPBs. The polarization resistance of optimally fired LSM‐YSZ electrodes increased upon thermal aging at 1,000 °C, whereas that of under‐fired electrodes decreased upon aging. These results are explained in terms of observed 3D microstructural changes.

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Firing Temperature Effect on 3D Microstructure and Performance of LSM-YSZ Composite SOFC Cathodes

Cited by 5 publications

References 25 publications

Electrochemical Performance of Solid Oxide Cell Oxygen Electrodes Under Pressurization

Electrochemical Performance of Solid Oxide Cell Oxygen Electrodes Under Pressurization

Durability Testing of Solid Oxide Cell Electrodes with Current Switching

Studies of Solid Oxide Fuel Cell Electrode Evolution Using 3D Tomography

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