Cathode Materials and Performance in High-Temperature Zirconia Electrolyte Fuel Cells

Tedmon, C. S.; Spacil, H. S.; Mitoff, S. P.

doi:10.1149/1.2412271

Cited by 194 publications

(110 citation statements)

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“…[1][2][3][4][5] In particular, among those applications, TMOs with mixed valence states have attracted attention for many environmental and renewable energy applications, including catalysts, hydrogen generation from water splitting, cathodes in rechargeable batteries and solid oxide fuel cells, and oxygen separation membranes. [6][7][8] For example, previous studies have shown that the ability to control the number of d-band electron population and detailed spin configuration in TMOs is critical for improved catalytic performance of TMOs. [9,10] In this context, SrCoO x (2.5 ≤ x ≤ 3.0) is an ideal class of materials to study the evolution of the physical properties by modifying the valence state in TMOs, due to the existence of two structurally distinct topotactic phases, i.e.…”

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confidence: 99%

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

et al. 2013

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Oxygen stoichiometry is one of the most important elements in determining the physical properties of transition metal oxides (TMOs). A small change in the oxygen content results in the variation of valence state of the transition metal, drastically modifying the materials functionalities. The latter includes, for instance, (super-)conductivity, magnetism, ferroelectricity, bulk ionic conduction, and catalytic surface reactions. [1][2][3][4][5] In particular, among those applications, TMOs with mixed valence states have attracted attention for many environmental and renewable energy applications, including catalysts, hydrogen generation from water splitting, cathodes in rechargeable batteries and solid oxide fuel cells, and oxygen separation membranes. [6][7][8] For example, previous studies have shown that the ability to control the number of d-band electron population and detailed spin configuration in TMOs is critical for improved catalytic performance of TMOs. [9,10] In this context, SrCoO x (2.5 ≤ x ≤ 3.0) is an ideal class of materials to study the evolution of the physical properties by modifying the valence state in TMOs, due to the existence of two structurally distinct topotactic phases, i.e. the brownmillerite SrCoO 2.5 (BM-2 SCO) (see Figure 1a) and the perovskite SrCoO 3 . [11,12] Especially, BM-SCO has atomicallyordered one-dimensional vacancy channels (see Figure 1a), which can accommodate additional oxygen when the valence state of Co is changed. Moreover, SrCoO x exhibits a wide spectrum of physical properties from antiferromagnetic insulator to ferromagnetic metal depending on the oxygen stoichiometry. [11][12][13] Since SrCoO x has only a single control knob, i.e. the oxygen contentx, to modify the Co valence state without cation doping, it is straightforward to study the valence state (i.e. oxygen content) dependent physical properties. However, so far, the growth of high quality single crystalline materials has not been as successful due to difficulty in controlling the right oxidation state.In this work, we report on the epitaxial growth of high quality BM-SCO single crystalline films on SrTiO 3 (STO) substrates by pulsed laser epitaxy (PLE). In order to examine the topotactic phase transformation to the perovskite SrCoO 3- (P-SCO), some of the samples were subsequently in-situ annealed at various oxygen pressure (P(O 2 )) to fill the oxygen vacancies.While the direct growth of P-SCO films with x = 3.0 was an arduous task, we found that postannealing in high P(O 2 ) (> several hundreds of Torr) could fill sufficient amount of oxygen vacancies, yielding systematic evolution in electronic, magnetic, and thermoelectric properties. (Figure 1b) demonstrate that the films are of high quality. X-ray rocking curve ω-scans revealed a full width half maximum (FWHM) of < 0.04º, demonstrating the excellent crystallinity (cf., FWHM of the 002 STO peak was ~0.02º) of our films (data not shown).While we have shown the XRD data from a well-optimized, high quality thin film, it is worthwhile to mention tha...

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confidence: 99%

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

et al. 2013

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“…The dominant phase, which was observed both in the contact layer and the porous cathode, was Ag 2 (Cr,Mn)O 4 , while only very small amounts of Ag(Cr,Mn)O 2 were detected in the contact layer. The compound Ag 2 CrO 4 is known to have a decomposition temperature of 665°C [25,26], which is well below the melting temperature of pure Ag (962 o C) [27], and also well below the test temperature of our cells (800°C). After reaching its decomposition temperature, Ag 2 CrO 4 is expected to convert to AgCrO 2 and Ag, following the reaction below [25].…”

Section: Microstructural Evaluationmentioning

confidence: 76%

Novel Composite Materials for SOFC Cathode-Interconnect Contact

Zhu¹

2009

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“…We postulate that the high oxygen solubility ([O]) in Ag, not the molecular O 2 transport, 20 becomes the primary oxygen source to sustain the ORR during EIS measurements under OCV condition. It could present a problem in real SOFC testing where a greater oxygen flux is required to support a greater cell current.…”

Section: Resultsmentioning

confidence: 99%

“…8,[16][17][18][19] However, due to its low melting temperature (962 • C) and high vapor pressure, 10 silver has a great propensity to be volatile and mobile at elevated temperatures. 20 If Ag migrates into the cathode microstructure as a result of its high mobility, and gets involved in the local electrochemical reactions, its known excellent ORR catalytic activity could overshadow the true performance of the cathode under investigation, resulting in misleading conclusions. Therefore, use of Ag as a cathode current collector at elevated temperatures should proceed with caution.…”

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Can Silver Be a Reliable Current Collector for Electrochemical Tests?

Gong

Qin

Huang

2012

ECS Electrochemistry Letters

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The true functionality of a current collector employed in electrochemical cells is to ensure a low-resistance steady electrons flow between the cell and instrumentation without involving in any local electrochemical reactions of the electrode. In this study, we investigated the effect of curing temperature of a common current collector, silver, on the polarization area specific resistance (ASR) of a cathode. The results explicitly showed that at least one order of magnitude lower ASR for a cathode with Ag cured at 800 • C than that cured at 650 • C of the same cathode configuration. Microscopic analysis of the 800 • C-cured cells revealed a deep penetration and abundant distribution of Ag into the cathode/electrolyte interfacial region. These finely dispersed and highly conductive Ag particles/agglomerates are ORR (oxygen reduction reaction)-active, thus engaging in the local electrochemical reaction and overshadowing the true properties of the cathode under investigation. Based on these results, we call for caution when using Ag as a current collector for electrochemical measurements, particularly at a temperature ≥650 • C. © 2012 The Electrochemical Society. [DOI: 10.1149/2.010301eel] All rights reserved.Manuscript submitted September 11, 2012; revised manuscript received October 23, 2012. Published November 6, 2012 Recent efforts in the development of solid oxide fuel cells have been focusing on exploring new electrode materials and optimizing microstructure.1-4 A general strategy to evaluate the performance of an electrode in a laboratory setting is to study its electrochemical behaviors in symmetrical cell or single cell configuration with either DC conductivity or AC impedance technique. In order to fulfill the electrical connection between the electrode and external instrumentation, a pair of metallic films necessary for collecting current is typically applied to the surfaces of the electrode. A good current collector should act solely as an interfacial electronic conductor to relay electrons from the cell to the measuring instrument; it should not participate in any local electrochemical reactions of the electrodes. 5,6 So far, the most popular current collectors of choice in electrochemical characterizations are found among noble metals such as Ag, Pt, and Au. In particular, Ag is a favored choice for cathode studies below 800• C because of its affordable cost and high electronic conductivity. 7-15On the other hand, silver is also known for its excellent oxygen reduction reaction (ORR) activity. Therefore, it has been intentionally utilized as a performance enhancer for cathodes La(Sr)Fe(Co)O 3 (LSCF), La(Sr)FeO 3 (LSF) and La(Sr)CoO 3 (LSCo) in SOFC research. 8,[16][17][18][19] However, due to its low melting temperature (962 • C) and high vapor pressure, 10 silver has a great propensity to be volatile and mobile at elevated temperatures. 20 If Ag migrates into the cathode microstructure as a result of its high mobility, and gets involved in the local electrochemical reactions, its known excellent ORR ...

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Cathode Materials and Performance in High-Temperature Zirconia Electrolyte Fuel Cells

Cited by 194 publications

References 9 publications

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

Novel Composite Materials for SOFC Cathode-Interconnect Contact

Can Silver Be a Reliable Current Collector for Electrochemical Tests?

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Cathode Materials and Performance in High-Temperature Zirconia Electrolyte Fuel Cells

Cited by 194 publications

References 9 publications

Topotactic Phase Transformation of the Brownmillerite SrCoO2.5 to the Perovskite SrCoO3–δ

Topotactic Phase Transformation of the Brownmillerite SrCoO2.5 to the Perovskite SrCoO3–δ

Novel Composite Materials for SOFC Cathode-Interconnect Contact

Can Silver Be a Reliable Current Collector for Electrochemical Tests?

Contact Info

Product

Resources

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Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ

Topotactic Phase Transformation of the Brownmillerite SrCoO_2.5 to the Perovskite SrCoO_3–_δ