Geometric Properties of Nanostructured Solid Oxide Fuel Cell Electrodes

Zhang, Yanxiang; Sun, Qiang; Xia, Changrong; Ni, Meng

doi:10.1149/2.057303jes

Cited by 85 publications

(102 citation statements)

References 29 publications

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“…• , the TPB length reaches a maximum and then decreases as the surface coverage fraction χ increases, similar to what reported by Zhang et al, 34 who imposed a contact angle among infiltrated particles of 60…”

Section: Resultssupporting

confidence: 86%

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A Particle-Based Model for Effective Properties in Infiltrated Solid Oxide Fuel Cell Electrodes

Bertei

Pharoah

Gawel

et al. 2014

J. Electrochem. Soc.

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A modeling framework for the numerical reconstruction of the microstructure of infiltrated electrodes is presented in this study. A particle-based sedimentation algorithm is used to generate the backbone, while a novel packing algorithm is used to randomly infiltrate nanoparticles on the surface of backbone particles. The effective properties, such as the connected triple-phase boundary length, the effective conductivity, the effective diffusivity, are evaluated on the reconstructed electrodes by using geometric analysis, finite volume and random-walk methods, and reported in dimensionless form to provide generality to the results. A parametric study on the effect of the main model and operating parameters is performed. Simulations show that the critical loading (i.e., the percolation threshold) increases as the backbone porosity decreases and the nanoparticle diameter increases. Large triple-phase boundary length, specific surface area and good effective conductivity can be reached by infiltration, without detrimental effects on the effective transport properties in gas phase. Simulations reveal a significant sensitivity to the size and contact angle of infiltrated particles, suggesting that the preparation process of infiltrated electrodes should be properly tailored in order to obtain the optimized structures predicted by the model. In the last decade, much attention has been drawn toward nanostructured electrodes for solid oxide fuel cells (SOFCs) prepared via infiltration techniques.1-7 The main reason is reduced polarization resistance, with corresponding increased power density, in comparison with conventional electrodes prepared via traditional mixing and sintering processes. The improved performance of infiltrated electrodes holds even at intermediate temperatures (500-800• C), as demonstrated by a large number of experimental studies. [8][9][10][11][12][13] Other technological advantages are a wide choice of catalyst materials, a good adhesion and a reduced thermal expansion mismatch between the electrode and the electrolyte.3 On the other hand, the long-term stability and the fabrication cost of nanostructured electrodes still need to be properly addressed. 2,3The infiltration (or impregnation) technique involves the deposition of nanoparticles into a pre-sintered backbone of micrometer-size particles.1,3 The backbone is a skeletal structure typically composed of a single component, such as yttria-stabilized zirconia (YSZ) 5,8 or, in alternative, a mixed ionic-electronic conductor (e.g., lanthanum strontium cobalt ferrite LSCF).14 However, composite backbones, such as the usual lanthanum strontium manganite (LSM)/YSZ cathode, have also been used. 1,15 The sintering of the backbone is performed at high temperature in order to ensure structural stability of the electrode and good connection among backbone particles. 3 In the following step, nanoparticles are infiltrated in the backbone using different methods (such as metal salt precipitation, 2 nanoparticle dispersion, 16 molten salts) 1 and then sinte...

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Section: Resultssupporting

confidence: 86%

“…Although the model shows some similarities with the Zhang et al 34 algorithm, it does not require any domain discretization to compute the TPB length and the surface area of infiltrated particles. In addition, a larger domain size is used as a result of a domain sensitivity analysis.…”

mentioning

confidence: 99%

A Particle-Based Model for Effective Properties in Infiltrated Solid Oxide Fuel Cell Electrodes

Bertei

Pharoah

Gawel

et al. 2014

J. Electrochem. Soc.

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“…9 A more recent report by Zhang et al utilized a numerically generated three-dimensional geometry. 17 In this work the percolation probabilities of pores and infiltrated nanoparticles, TPB density, and surface areas of the scaffold, infiltrate, and scaffold-infiltrate interface were predicted. A weighted risk factor for the aggregation of infiltrated particles was also considered.…”

mentioning

confidence: 99%

Insights into the Design of SOFC Infiltrated Electrodes with Optimized Active TPB Density via Mechanistic Modeling

Reszka

Snyder

Gross

2014

J. Electrochem. Soc.

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A mechanistic model for the prediction of total and active three phase boundary density (TPB), in combination with effective conductivity, of infiltrated solid oxide fuel cell (SOFC) electrodes is presented. Varied porosities, scaffold:infiltrate size ratios, and pore:infiltrate size ratios were considered, each as a function of infiltrate loading. The results are presented in dimensionless form to allow for the calculation of any infiltrate particle size. The model output compares favorably to the available experimental result. The results show that the scaffold:infiltrate size ratio has the greatest impact on the TPB density, followed by the porosity and then the pore:infiltrate size ratio. The TPB density is shown to monotonically decrease with increasing scaffold:infiltrate and pore:infiltrate size ratios; however, it shows a maximum with respect to porosity. Each of these results are explained by examining the interfacial areas of each of the three phases as a function of the infiltrate loading. The model provides insight toward the rational design of infiltrated electrodes. Infiltrated solid oxide fuel cell (SOFC) electrodes offer numerous advantages over conventional co-sintered electrodes. First, a broader choice of electrode materials is possible because materials that melt or chemically react with the electrolyte at conventional sintering temperatures can be considered.1-6 Second, a higher three-phase boundary (TPB) density can be achieved, which is attributed to the smaller particle sizes.2,3,7-9 These two advantages result from a lower processing temperature of the infiltrated phase compared to conventional sintering temperatures required of co-sintered electrodes.Three additional advantages of infiltrated electrodes are associated with the unique morphology created by coating the surface of a presintered porous scaffolding with an infiltrated phase. The first morphological advantage is a mitigation of the coefficient of thermal expansion (CTE) mismatch between the electrolyte and the electrode. 10,11The second advantage is a stabilization of the electrode mechanical properties during redox cycling, 5,12 Finally, less material is needed to form an interconnected network of the infiltrated phase throughout the electrode. 6,10,[12][13][14][15] Although the benefits of infiltrated electrodes have been clearly demonstrated experimentally, researchers suggest that the electrode designs are not optimized. 3,5,6,14,16 This is understandable because it is laborious to consider all of the combinations and permutations of the sizes and shapes of infiltrate particles, scaffold particles, and pores as well as the wide range of possible porosities. In order to more effectively and efficiently design electrodes, several computational models have been recently reported. Zhang et al. utilized a particle-layer model to estimate the TPB density, effective thickness of the electrochemically active region, and polarization resistance of cathodes.9 A more recent report by Zhang et al. utilized a numerically generated thr...

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“…In the anode, TPB exist at the interface of nickel and ionic conductors, which can be well evaluated through the micro Monte Carlo model developed by Zhang et al [20][21][22] …”

Section: Electrochemistrymentioning

confidence: 99%

Elementary reaction modeling and experimental characterization of solid oxide fuel-assisted steam electrolysis cells

Luo

Shi

et al. 2014

International Journal of Hydrogen Energy

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Geometric Properties of Nanostructured Solid Oxide Fuel Cell Electrodes

Cited by 85 publications

References 29 publications

A Particle-Based Model for Effective Properties in Infiltrated Solid Oxide Fuel Cell Electrodes

A Particle-Based Model for Effective Properties in Infiltrated Solid Oxide Fuel Cell Electrodes

Insights into the Design of SOFC Infiltrated Electrodes with Optimized Active TPB Density via Mechanistic Modeling

Elementary reaction modeling and experimental characterization of solid oxide fuel-assisted steam electrolysis cells

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