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Title: Synchrotron X-Ray Studies of Model SOFC Cathodes, Part I: Thin Film Cathodes.

Abstract

We present synchrotron x-ray investigations of thin film La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ (LSCF) model cathodes for solid oxide fuel cells, grown on electrolyte substrates by pulse laser deposition, in situ during half-cell operations. We observed dynamic segregations of cations, such as Sr and Co, on the surfaces of the film cathodes. The effects of temperature, applied potentials, and capping layers on the segregations were investigated using a surfacesensitive technique of total external reflection x-ray fluorescence. We also studied patterned thin film LSCF cathodes using high-resolution micro-beam diffraction measurements. We find chemical expansion decreases for narrow stripes. This suggests the expansion is dominated by the bulk pathway reactions. The chemical expansion vs. the distance from the electrode contact was measured at three temperatures and an oxygen vacancy activation energy was estimated to be ~1.4 eV.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; National Science Foundation (NSF); USDOE Office of Science - Office of Basic Energy Sciences - Scientific User Facilities Division
OSTI Identifier:
1411043
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Solid State Ionics; Journal Volume: 311
Country of Publication:
United States
Language:
English

Citation Formats

Chang, Kee-Chul, Ingram, Brian, Ilavsky, Jan, Lee, Shiwoo, Fuoss, Paul, and You, Hoydoo. Synchrotron X-Ray Studies of Model SOFC Cathodes, Part I: Thin Film Cathodes.. United States: N. p., 2017. Web. doi:10.1016/j.ssi.2017.10.005.
Chang, Kee-Chul, Ingram, Brian, Ilavsky, Jan, Lee, Shiwoo, Fuoss, Paul, & You, Hoydoo. Synchrotron X-Ray Studies of Model SOFC Cathodes, Part I: Thin Film Cathodes.. United States. doi:10.1016/j.ssi.2017.10.005.
Chang, Kee-Chul, Ingram, Brian, Ilavsky, Jan, Lee, Shiwoo, Fuoss, Paul, and You, Hoydoo. 2017. "Synchrotron X-Ray Studies of Model SOFC Cathodes, Part I: Thin Film Cathodes.". United States. doi:10.1016/j.ssi.2017.10.005.
@article{osti_1411043,
title = {Synchrotron X-Ray Studies of Model SOFC Cathodes, Part I: Thin Film Cathodes.},
author = {Chang, Kee-Chul and Ingram, Brian and Ilavsky, Jan and Lee, Shiwoo and Fuoss, Paul and You, Hoydoo},
abstractNote = {We present synchrotron x-ray investigations of thin film La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) model cathodes for solid oxide fuel cells, grown on electrolyte substrates by pulse laser deposition, in situ during half-cell operations. We observed dynamic segregations of cations, such as Sr and Co, on the surfaces of the film cathodes. The effects of temperature, applied potentials, and capping layers on the segregations were investigated using a surfacesensitive technique of total external reflection x-ray fluorescence. We also studied patterned thin film LSCF cathodes using high-resolution micro-beam diffraction measurements. We find chemical expansion decreases for narrow stripes. This suggests the expansion is dominated by the bulk pathway reactions. The chemical expansion vs. the distance from the electrode contact was measured at three temperatures and an oxygen vacancy activation energy was estimated to be ~1.4 eV.},
doi = {10.1016/j.ssi.2017.10.005},
journal = {Solid State Ionics},
number = ,
volume = 311,
place = {United States},
year = 2017,
month =
}
  • Infiltrated La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) sintered porous powder cathodes for solid oxide fuel cells have been investigated by synchrotron ultra-small angle x-ray scattering (USAXS). We demonstrated that atomic layer deposition (ALD) is the method for a uniform coating and liquid-phase infiltration for growing nanoscale particles on the porous LSCF surfaces. The MnO infiltrate, grown by ALD, forms a conformal layer with a uniform thickness throughout the pores evidenced by USAXS thickness fringes. The La0.6Sr0.4CoO3 (LSC) and La2Zr2O7 (LZO) infiltrates, grown by liquid-phase infiltration, were found to form nanoscale particles on the surfaces of LSCF particles resulting in increased surface areas. Impedance measurementsmore » suggest that the catalytic property of LSC infiltrate, not the increased surface area of LZO, is important for increasing oxygen reduction activities.« less
  • Using a model cathode-electrolyte system composed of epitaxial thin-films of La{sub 1-x}Sr{sub x}MnO{sub 3-{delta}} (LSM) on single crystal yttria-stabilized zirconia (YSZ), we investigated changes in the cation concentration profile in the LSM during heating and under applied potential using grazing incidence x-rays. Pulsed laser deposition (PLD) was used to grow epitaxial LSM(011) on YSZ(111). At room temperature, we find that Sr segregates to form Sr enriched nanoparticles and upon heating the sample to 700 C, Sr is slowly reincorporated into the film. We also find different amounts of Sr segregation as the X-ray beam is moved across the sample. Themore » variation in the amount of Sr segregation is greater on the sample that has been subject to 72 hours of applied potential, suggesting that the electrochemistry plays a role in the Sr segregation.« less
  • Sol-gel technology presents an attractive possibility as an alternative method for producing alkaline batteries, specifically in a thin-film configuration. The cathode material prepared via sol-gels proved to perform better in terms of both energy and power output compared to conventional MnO{sub 2} electrodes. Procedures for the cathode fabrication are summarized, and the electrochemical performance of the cathode under various discharge conditions is presented.
  • We have successfully developed a method for fabricating scandate-based thermionic emitters in thin film form. The primary goal of our effort is to develop thin film emitters that exhibit low work function, high intrinsic electron emissivity, minimum thermal activation properties and that can be readily incorporated into a microgap converter. Our approach has been to incorporate BaSrO into a Sc{sub 2}O{sub 3} matrix using rf sputtering to produce thin films. Diode testing has shown the resulting films to be electron emissive at temperatures as low as 900 K with current densities of 0.1 mA{center_dot}cm{sup {minus}2} at 1100 K and saturationmore » voltages. We calculate an approximate maximum work function of 1.8 eV and an apparent emission constant (Richardson{close_quote}s constant, A{sup {asterisk}}) of 36 mA{center_dot}cm{sup {minus}2}{center_dot}K{sup {minus}2}. Film compositional and structural analysis shows that a significant surface and subsurface alkaline earth hydroxide phase can form and probably explains the limited utilization and stability of Ba and its surface complexes. The flexibility inherent in sputter deposition suggests alternate strategies for eliminating undesirable phases and optimizing thin film emitter properties. {copyright} {ital 1999 American Institute of Physics.}« less
  • Thin-film rechargeable lithium batteries with amorphous and crystalline LiCoO{sub 2} cathodes were investigated. The lithium cobalt oxide films were deposited by radio-frequency (RF) magnetron sputtering of an LiCoO{sub 2} target in a 3:1 Ar/O{sub 2} mixture gas. From proton-induced {gamma}-ray emission analysis (PIGE) and Rutherford backscattering spectrometry (RBS), the average composition of these films was determined to be Li{sub 1.15}CoO{sub 2.16} or, within experimental uncertainty, LiCoO{sub 2} + 0.08 Li{sub 2}O. The X-ray powder diffraction patterns of films annealed in air at 500 to 700 C were consistent with the regular hexagonal structure observed for crystalline LiCoO{sub 2}. The dischargemore » curves of the cells with amorphous LiCoO{sub 2} cathodes showed no obvious structural transition between 4.2 and 2.0 V, while the discharge curves of the cells with polycrystalline cathodes were consistent with a two-phase potential plateau at {approximately}3.9 V with a relatively large capacity. Two lower capacity plateaus were observed at {approximately} 4.2 and 4.1 V with the 600 and 700 C annealed cathodes; the {minus}dq/dV peaks were broader and weaker for the 600 C annealed cathodes and were not present at all with the 500 C annealed films. The chemical diffusion coefficients of Li{sup +} in the cathodes obtained from ac impedance measurements at cell potentials of {approximately} 4 V ranged from {approximately} 10{sup {minus}12} cm{sup 2}/s for the as-deposited amorphous cathodes to {approximately} 10{sup {minus}9} cm{sup 2}/s for the films annealed at 700 C. The capacity loss on extended cycling of the thin-film cells varied with the crystallinity and thickness of the cathodes and with temperature. With the highly crystalline, 700 C annealed material, losses on cycling between 4.2 and 3.8 V at 25 C ranged from 0.0001%/cycle (> 10{sup 4} cycles) to 0.002%/cycle for cells with cathodes form 0.05 to 0.5 {micro}m thick.« less