Catalytic properties of La1−A′ MnO3 (A′ = Sr, Ce, Hf)

Nitadori, Taihei; Kurihara, Shigeo; Misono, Makoto

doi:10.1016/0021-9517(86)90310-6

Cited by 144 publications

(28 citation statements)

References 16 publications

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“…• C. These exchange peaks are consistent with previous temperature programmed desorption (TPD) data, 44,45 and are a result of the change in valance state of Mn. The formation of 16 O 18 O begins at 300…”

Section: Resultssupporting

confidence: 90%

“…The temperature and PO 2 regions that have the highest interaction between water and cathodes are also correlated to valance state changes for the B-site transition metals. 44,45 In a full cell, the cathode may experience relative water to oxygen concentrations significantly higher than ambient, through oxygen depletion at high currents or gas leaks from the anode side of the cell. Moreover, ambient humidity can change dramatically with season and geographic location.…”

Section: Resultsmentioning

confidence: 99%

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Fundamental Impact of Humidity on SOFC Cathode ORR

Huang

Pellegrinelli

Wachsman

2015

J. Electrochem. Soc.

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Although solid oxide fuel cells (SOFC) have demonstrated excellent performance, the durability of SOFCs under real working conditions is still an issue for commercial deployment. In particular cathode exposure to atmospheric air contaminants, such as humidity, can result in long-term performance degradation issues. Therefore, a fundamental understanding of the interaction between water molecules and cathodes is essential to resolve this issue and further enhance cathode durability. To study the effects of humidity on the oxygen reduction reaction (ORR), we used in-situ 18 O isotope exchange techniques to probe the exchange of water with two of the most common SOFC cathode materials, (La 0.8 Sr 0.2 ) 0.95 MnO 3±δ (LSM) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF). In this experiment, heavy water, D 2 O (with a mass/charge ratio of m/z = 20), is used to avoid the overlapping of H 2 O and the 18 O 2 cracking fraction, which both provide a peak at m/z = 18. A series of temperature programmed isotope exchange measurements were performed to comprehensively study the interaction of water with the cathode surface as a function of temperature, oxygen partial pressure, and water vapor concentration. The results suggest that water and O 2 share the same surface exchange sites, leading to competitive adsorption. Our findings show that water prefers to exchange with LSCF at lower temperatures, around 300-450 • C. For LSM, O 2 is more favorable than water to be adsorbed on the surface and the presence of O 2 limits water exchange. The experimental data are summarized in a Temperature-PO 2 diagram to help visualize how the exchange of water on each material depends on the operating conditions. © The Author Solid oxide fuel cells (SOFC) electrochemically oxidize fuels for the generation of electricity. Two key advantages of SOFCs are their high efficiency and ability to utilize conventional fuels. This fuel flexibility stems from the dissociation and transport of oxygen from the cathode through the electrolyte to the anode, where the fuels are oxidized. Unfortunately, cathode degradation under real working conditions is a factor that limits SOFC performance. 1-6The long term durability of these materials is a major challenge, due to the high temperature required for the thermally activated oxygen reduction reaction (ORR), 7 as well as the variety of gases present during operation. 8,9 The impurities present in air on the cathode side of the cell can induce undesirable reactions. Some of these impurities, such as Cr or silica, 10-15 arise due to the interconnect and seal materials while some are intrinsic to ambient air, such as humidity and CO 2 . 16 Humidity has been found to degrade the performance of (La 0.8 Sr 0.2 ) 0.95 MnO 3±δ (LSM) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) based cells. 11,[17][18][19][20][21][22][23][24] This degradation can be either reversible or irreversible. 21 However, there is no conclusive evidence showing, fundamentally, how water participates in the degradation process, and it is hard to quan...

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Fundamental Impact of Humidity on SOFC Cathode ORR

Huang

Pellegrinelli

Wachsman

2015

J. Electrochem. Soc.

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“…It can be seen that the amount of C 0 2 formed per pulse depends on the recovery time between successive pulses. If CO pulses arc injected at short intervals, a decrease in the amount of C 0 2 formed per pulse has been observed by Nitadori et al [5]. In this investigation, CO injections were repeated at regular time intervals until a constant value for the C 0 2 produced was reached; this steady state value is plotted against the time between pulses in the figure.…”

Section: Pulsed Reductionmentioning

confidence: 60%

“…It has frequently been observed that oxygen from the surface layer ("surface lattice oxygen") as well as the bulk ("bulk lattice oxygen") participate in the reaction. This has been verified in a series of experiments using labelled oxygen '*O or "0 [4][5][6].…”

Section: Introductionmentioning

confidence: 77%

Catalytic CO Oxidation over La_1‐xSrxMnO₃ at High CO Partial Pressures

Jaenicke

Chuah

1992

Ber Bunsenges Phys Chem

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The catalytic CO oxidation over polycrystalline LaMn03 exhibits a bistability at high CO concentration. Under atmospheric pressure, the regime of bistability extends from 200 to 220°C and widens with increasing CO concentration. A systematic study of the solid solution system La, -,Sr,MnO, which crystallizes in the pcrovskite structure, shows that the width of the bistable regime decreases with an increasing amount of strontium substitution and no bifurcation was observed for x > 0.2. A model is proposed to explain the bistability, based on a CO-driven reconstruction of the reduced surface, leading to pairs of Mn2 ions with a Mn-Mn distance comparable to the spacing in the metal. These pairs provide reactive sites for CO oxidation and oxygen chemisorption. Such metal-metal pairs are not found in the perovskite lattice but are a structural feature of the closely related hexagonal 4-layered packing which is the normal crystal structure of SrMnO,. The rate of change back to the "oxidized" surface is found to correlate with the lattice oxygen mobility. With low oxygen mobility, the transition from the active into the less active state becomes slow and hysteresis may result. Strontium substitution increases the number of defects in the oxygen lattice and leads ultimately to an oxygen deficiency (reductive nonstoichiometry). The catalytic activity of the system peaks at x = 0.2, indicating the influence of both the oxygen mobility and the oxygen nonstoichiometry on the catalytic oxidation reaction.

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“…Larger 12-coordinate A cations and smaller 6-coordinate B cations can be relatively easily substituted by various metal cations, which often results in an oxygen non-stoichiometry such as oxygen excess or deficiency. [5] The structural variations arising from the defects enable catalytic reactions including both oxidation and reduction. [6] In particular, lanthanide-based perovskites have shown remarkable performance as high temperature catalysts in solid oxide fuel cell devices and as gas-solid phase heterogeneous catalysts (CO oxidation or methane oxidation).…”

mentioning

confidence: 99%

Major Role of Surface Area in Perovskite Electrocatalysts for Alkaline Systems

Hwang

Gwon

et al. 2017

ChemElectroChem

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We investigate the role of lanthanides and the surface area of perovskite oxides to determine the electrocatalytic properties in processes such as the oxygen reduction and evolution reactions. To evaluate the effects of A‐site lanthanide and the surface area, a series of lanthanide‐based perovskite nanoparticles (LnSCs) were successfully synthesized with simple co‐precipitation methods, and electrochemical tests were carried out with the LnSCs. According to the results, the catalytic activities are not affected by the A‐site lanthanides, but the surface area was found to be related to the current densities of the perovskite catalysts.

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Catalytic properties of La1−A′ MnO3 (A′ = Sr, Ce, Hf)

Cited by 144 publications

References 16 publications

Fundamental Impact of Humidity on SOFC Cathode ORR

Fundamental Impact of Humidity on SOFC Cathode ORR

Catalytic CO Oxidation over La_1‐xSrxMnO₃ at High CO Partial Pressures

Major Role of Surface Area in Perovskite Electrocatalysts for Alkaline Systems

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Catalytic properties of La1−A′ MnO3 (A′ = Sr, Ce, Hf)

Cited by 144 publications

References 16 publications

Fundamental Impact of Humidity on SOFC Cathode ORR

Fundamental Impact of Humidity on SOFC Cathode ORR

Catalytic CO Oxidation over La1‐xSrxMnO3 at High CO Partial Pressures

Major Role of Surface Area in Perovskite Electrocatalysts for Alkaline Systems

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Product

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Catalytic CO Oxidation over La_1‐xSrxMnO₃ at High CO Partial Pressures