Quantitative analysis of solid oxide fuel cell anode microstructure change during redox cycles

Shimura, Takaaki; Jiao, Zhenjun; Hara, Shotaro; Shikazono, Naoki

doi:10.1016/j.jpowsour.2014.04.152

Cited by 54 publications

(60 citation statements)

References 30 publications

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“…Therefore, distributions characterized by a mean value closer to zero and by a low standard deviation are intuitively indicative of a microstructure that provides high accessibility to TPB sites and that is uniformly utilized. It is therefore beneficial to maximize performance and reduce vulnerability against degradation phenomena that alter the morphology and topology of the material phases and the spatial distribution of the TPBs, such as coarsening and reduction-oxidation cycling of Ni in Ni-YSZ [6,8,[16][17][18].…”

Section: Figurementioning

confidence: 99%

“…The clear presence of preferential pathways showcases a non-uniform utilization of the 3-D structure that potentially affects the performance and the resilience to alterations due to degradation phenomena in electrochemical energy storage and conversion devices. our understanding of the detrimental effects of microstructural coarsening, contamination or redox cycling in SOFC/SOEC materials [6,8,[16][17][18][19][20][21][22][23].A main limitation of approaches based on averaged (e.g. effective) properties is that all the TPBs are treated as equally accessible.…”

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confidence: 99%

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Accessible triple-phase boundary length: A performance metric to account for transport pathways in heterogeneous electrochemical materials

Nakajo

Cocco

DeGostin

et al. 2016

Journal of Power Sources

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The performance of materials for electrochemical energy conversion and storage depends upon the number of electrocatalytic sites available for reaction and their accessibility by the transport of reactants and products. For solid oxide fuel/electrolysis cell materials, standard 3-D measurements such as connected triple-phase boundary (TPB) length and effective transport properties partially inform on how local geometry and network topology causes variability in TPB accessibility. A new measurement, the accessible TPB, is proposed to quantify these effects in detail and characterize material performance.The approach probes the reticulated pathways to each TPB using an analytical electrochemical fin model applied to a 3-D discrete representation of the heterogeneous structure provided by skeleton-based partitioning. The method is tested on artificial and real structures imaged by 3-D x-ray and electron microscopy. The accessible TPB is not uniform and the pattern varies depending upon the structure. Connected TPBs can be even passivated.The sensitivity to manipulations of the local 3-D geometry and topology that standard measurements cannot capture is demonstrated. The clear presence of preferential pathways showcases a non-uniform utilization of the 3-D structure that potentially affects the performance and the resilience to alterations due to degradation phenomena in electrochemical energy storage and conversion devices. our understanding of the detrimental effects of microstructural coarsening, contamination or redox cycling in SOFC/SOEC materials [6,8,[16][17][18][19][20][21][22][23].A main limitation of approaches based on averaged (e.g. effective) properties is that all the TPBs are treated as equally accessible. The visual inspection of 3-D imaging data suggests that this assumption is questionable and that significant local information is lost. In contrast, the TPB tortuosity and TPB critical pathway radius have been recently proposed for the characterization of the transport pathways to TPBs [24]. This approach, based on image processing, provides new insight into the factors that control the electrochemical performance of heterogeneous materials, but it is based on purely geometric concepts that highlight two specific and mostly local properties of the reticulate pathways, i.e. the shortest path length and the smallest constriction that must be passed through to access a TPB. Simulations based on lattice Boltzmann or finite element method that use as computational domain the imaged and meshed 3-D structures [4,25] are capable of quantifying accurately the access to TPB, including the combined effects of local 3-D geometrical features and topology of the microstructure. However, attempts to define dedicated TPB properties that inform on material performance and durability have been limited so far [4], partly because of the high computational requirements.An analytical electrochemical fin model (ECF) has been developed as a screening tool for material design [26][27][28][29]. The method consists in represen...

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Section: Figurementioning

confidence: 99%

mentioning

confidence: 99%

Accessible triple-phase boundary length: A performance metric to account for transport pathways in heterogeneous electrochemical materials

Nakajo

Cocco

DeGostin

et al. 2016

Journal of Power Sources

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“…Concerning the changes in the materials composition and microstructure, scanning electron microcopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are useful techniques [3]. To obtain a full microstructural characterization of the electrode structures, focused ion beam-scanning electron microscopy (FIB-SEM) technique has been extensively used [19][20][21][22][23][24][25]. The microstructural details that can be extracted from 3D tomographic reconstructions such as particles size distribution [26] and triple phase boundary (TPB) length [19][20][21]25] provide quantification of microstructural features of the complex cermet structure.…”

Section: Introductionmentioning

confidence: 99%

3D Microstructural Characterization of Ni/YSZ Electrodes Exposed to 1 Year of Electrolysis Testing

Trini

Jørgensen²,

Bentzen³

et al. 2019

J. Electrochem. Soc.

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“…Further investigations are required to confirm this hypothesis. In particular, FIB-SEM tomography methods [64][65][66][67] could prove useful in linking BET and electron microscopy data in a more quantitative way.…”

Section: Discussionmentioning

confidence: 99%

Characterization and Stack Testing of Solid Oxide Fuel Cells with Cathodes Prepared by Infiltration

Hertz

Heiredal‐Clausen

2015

J. Electrochem. Soc.

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Large footprint (144 cm 2 ) cells with infiltrated (La 0.6 Sr 0.4 ) 0.95 FeO 3 /yttria-stabilized zirconia (LSF-YSZ) cathodes were fabricated on a pre-production scale (approximately 90 cells/batch). The excellent electrochemical performance of the cells was confirmed both on single cell as well as on stack level. Changes in electrode properties were mapped out as a function of heat-treatment temperature. The microstructure of the porous zirconia backbone remained unchanged, but the surface area of the ferrite phase decreased gradually, as the electrode was treated to higher temperatures. Changes in surface area were accompanied by corresponding changes in pore size and total pore volume. In contrast to traditional composite electrodes, the in-plane conductivity of infiltrated LSF-YSZ cathodes decreased with increasing sintering temperature, a trend likely explained by microstructure alterations during the sintering of the non-random structure. Recently, the use of infiltration as a method for solid oxide fuel cell (SOFC) electrode preparation has gathered significant scientific interest.1-6 The infiltration (or impregnation) method resembles the wet impregnation and incipient wetness methods employed in heterogeneous catalysis. 7,8 The electrodes are prepared by the introduction of perovskite precursors (e.g. in the form of nanoparticles, aqueous nitrate solutions, or molten salts 9 ) into sintered porous backbone structures, typically made of electrolyte materials such as yttria-stabilized zirconia (YSZ) 1,9-12 or doped ceria. 3,6,13 Such electrodes have several advantages over traditional SOFC electrodes. Infiltration approach allows for the use of a wider range of active materials.1,2,10,12,14 Furthermore, infiltrated electrodes promise improved mechanical properties over traditional electrodes due to the lower thermal expansion mismatch between the electrolyte and cathode layers, 1,10 and enhanced performance due to the high surface area of the active phase. 1,6,12,16 Finally, the possibility of synthesizing the electrode active phase in situ within the electrolyte pores from relatively cheap nitrate precursors may offer significant materials cost advantages over traditional electrodes, where expensive perovskite powders with finely tuned particle size distributions are required for screen-printing. 17The results on infiltrated electrodes reported in the literature have so far been obtained almost exclusively on button cells with electrode active areas on the order of 1 cm 2 or less. A notable exception is the work by C. S. Ni et al., who have recently fabricated and tested 5 × 5 cm 2 cells where both the anode and the cathode was prepared by infiltration. 18 Here, we report the physical characterization and stack testing of 12 × 12 cm 2 planar cells with cathodes prepared by infiltration of a perovskite precursor solution into a stabilized zirconia (SZ) backbone. The results reported here were obtained primarily on infiltrated (La 0.6 Sr 0.4 ) 0.95 FeO 3 (LSF)-SZ electrodes. LSF-SZ is an excellent model sy...

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Quantitative analysis of solid oxide fuel cell anode microstructure change during redox cycles

Cited by 54 publications

References 30 publications

Accessible triple-phase boundary length: A performance metric to account for transport pathways in heterogeneous electrochemical materials

Accessible triple-phase boundary length: A performance metric to account for transport pathways in heterogeneous electrochemical materials

3D Microstructural Characterization of Ni/YSZ Electrodes Exposed to 1 Year of Electrolysis Testing

Characterization and Stack Testing of Solid Oxide Fuel Cells with Cathodes Prepared by Infiltration

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