Anode microstructural change upon long-term operation for the cathode-supported tubular-type SOFC

Matsui, Toshiaki; Kim, Jin‐Young; Muroyama, Hiroki; Shimazu, Megumi; Abe, Toshiya; Miyao, Motoyasu; Eguchi, Koichi

doi:10.1016/j.ssi.2012.03.035

Cited by 28 publications

(29 citation statements)

References 12 publications

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“…A similar phenomenon is observed in the NGK SPARK PLUG anode by Kyoto University although the oxygen potential determined from CRIEPI's analyses shows that oxygen potential of this anode-electrolyte interface is far from the NiO-Ni borderline (see Fig.2), suggesting that additional mechanism contributes to this phenomenon. AIST's SIMS analyses revealed that a slight amount of phosphorous was present in the Ni retarded anode in a similar manner to the Ni degradation observed in TOTO's sealless tubular cells (11); AIST also observed the concentrated phosphorous in the Ni-YSZ interfaces of the TOTO cells. The thermodynamic analyses on phosphorous is given elsewhere (12) …”

Section: Oxygen Potential Distributionmentioning

confidence: 66%

Current Status of Rapid Evaluation of Durability of Six SOFC Stacks within Nedo Project

Yokokawa

2015

ECS Trans.

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Six solid oxide fuel cell stacks manufactured by Kyocera, Mitsubishi Hitachi Power Systems (MHPS), TOTO, NGK SPARK PLUG, NGK INSULATORS, and Murata Manufacturing have been investigated to identify their performance degradation behavior, extract major sources of degradations, clarify the degradation mechanism, and predict the time dependent contributions of such degradations to life time. Stack performance was analyzed into several contributions, and in addition to identification of respective degradation rates, an interesting correlation between the overpotential values and the ohmic losses has been extracted. Respective degradation issues have been examined experimentally with SIMS, FIB-SEM, STEM and described as key simulation matters to predict the long life up to 90,000 h. Emphases have been placed on degradation of cathodes with Cr or S; to ensure the appropriateness for overcoming such poisoning effects, care was exercised to measure the impurity level after long term operations in various environments. For simulation, focus was made to overcome some gaps between knowledge on stacks and on single (or buttons) cells appearing in several degradations.

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Section: Oxygen Potential Distributionmentioning

confidence: 66%

Current Status of Rapid Evaluation of Durability of Six SOFC Stacks within Nedo Project

Yokokawa

2015

ECS Trans.

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“…For the NTK planer cells, the cathode overpotential and the ohmic loss increase significantly at the beginning (see Figure a); despite a small degradation of anodes, impurities such as phosphor were detected in anodes and correspondingly the 3D reconstruction by FIB (focused ion beam) – SEM technique (Kyoto Univ.) indicates Ni depletion.…”

Section: Methods and Major Results Of Stack Performance Testmentioning

confidence: 99%

“…The second project in 2008–20012FY revealed that significantly degraded parts were strongly related with the fabrication sequence of stacks; namely, electrodes fabricated as a next step to the sintering of electrolyte. For example, the anodes in cathode supporting sealless tubular cells fabricated by TOTO exhibited significant degradations because of phosphor contamination . In addition, the second project found that some cell degradations become severer with decreasing temperature , while other degradations become significant with temperature as a typical activation process.…”

Section: Introductionmentioning

confidence: 99%

Recent Achievements of NEDO Durability Project with an Emphasis on Correlation Between Cathode Overpotential and Ohmic Loss

et al. 2017

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Long-term performance testes by CRIEPI (Central Research Institute for Electric Power Industry) on six industrial stacks have revealed an interesting correlation between cathode polarization loss and ohmic loss. To make clear the physicochemical meaning of this correlation, detailed analyses were made on the conductivity degradation of YSZ electrolyte in button cells and then on the ohmic losses in the industrial cells in terms of time constants which are determined from speed of the tetragonal transformation through the Y diffusion from the cubic phase to the tetragonal phase. In some cases, shorter time constants (faster degradations) were detected than those expected from the two-time-constant (with and without NiO reduction effects) model, suggesting that additional ohmic losses after subtracting the contribution from the tetragonal transformation must be caused from other sources such as cathode-degradation inducing effects. Main cathode degradations can be ascribed to sulfur poisoning due to contamination in air in the CRIEPI test site. An important feature was extracted as this cathode degradations became more severe when the gadolinium-doped ceria (GDC) interlayers were fabricated into dense film. Plausible mechanisms for cathode degradations were proposed based on the Sr/Co depletion on surface of lanthanum strontium cobalt ferrite (LSFC) in the active area. Peculiar cathode degradations found in stacks are interpreted in term of changes in surface concentration by reactions with sulfur oxide, electrochemical side reactions for water vapor emission or Sr volatilization, and diffusion of Sr/Co from inside LSCF.

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“…The limited durability of SOFCs over their expected lifetime continues to impede their widespread market penetration . The durability of SOFCs is tied closely to the distribution of microstructural features in the active electrodes generated during manufacture, as well as to their evolution during operation: several groups have specifically investigated the link between operation, electrode microstructural evolution, and performance degradation . The active electrode layers are typically porous composites containing an ion‐conducting phase, an electron‐conducting phase, and gas permeable pores .…”

Section: Introductionmentioning

confidence: 99%

Quantifying intermediate‐frequency heterogeneities of SOFC electrodes using X‐ray computed tomography

et al. 2017

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The electrodes in solid oxide fuel cells (SOFCs) consist of three phases interconnected in three dimensions. The volume needed to describe quantitatively such microstructures depends on several lengths scales, which are functions of materials properties and fabrication methods. This work focuses on quantifying the volume needed to represent “intermediate frequency” heterogeneities in electrodes of a commercial SOFC using X‐ray computed tomography (CT) over two different length scales. Electrode volumes of 150 μm × 150 μm × 9 μm were extracted from a synchrotron‐based micro‐CT data set, with 13 μm3 voxels. 13.6 μm × 19.8 μm × 19.4 μm of the cathode and 26.3 μm × 24.8 μm × 15.7 μm of the anode were extracted from laboratory nano‐CT data sets, both with 653 nm3 voxels. After comparing the variation across sub‐regions for the grayscale values from the micro‐CT, and for the phase fractions and triple phase boundary densities from the nano‐CT, it was found that the sub‐region length scales needed to yield statistically similar average values were an order of magnitude larger than those expected to capture the “high frequency” heterogeneity related to the discrete nature of the three phases in electrodes. The challenge of quantifying such electrodes using available experimental methods is discussed.

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Anode microstructural change upon long-term operation for the cathode-supported tubular-type SOFC

Cited by 28 publications

References 12 publications

Current Status of Rapid Evaluation of Durability of Six SOFC Stacks within Nedo Project

Current Status of Rapid Evaluation of Durability of Six SOFC Stacks within Nedo Project

Recent Achievements of NEDO Durability Project with an Emphasis on Correlation Between Cathode Overpotential and Ohmic Loss

Quantifying intermediate‐frequency heterogeneities of SOFC electrodes using X‐ray computed tomography

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