Reconstruction of porous electrodes by FIB/SEM for detailed microstructure modeling

Joos, Jochen; Carraro, Thomas; Weber, André; Ivers-Tiffée, Ellen

doi:10.1016/j.jpowsour.2010.10.006

Cited by 169 publications

(140 citation statements)

References 14 publications

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“…The porosity fraction (ε) was obtained by dividing the voxels assigned as pore by the total number of voxels, the surface area (a) was obtained by using the marching cube algorithm and the tortuosity of the solid-phase (τ MIEC ) was obtained by solving the transport equation directly from the 3D data tomography (as described in detail previous studies [25][26][27] ). The porosity fraction (ε) is slightly above 50% and similar for both BSCF and LSCF cathodes, although the average particle size of the LSCF (d LSCF = 282 nm) is smaller than that of the BSCF (d BSCF = 567 nm).…”

Section: Resultsmentioning

confidence: 99%

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Oxygen Transport Kinetics of Mixed Ionic-Electronic Conductors by Coupling Focused Ion Beam Tomography and Electrochemical Impedance Spectroscopy

Almar

Szász

Weber

et al. 2017

J. Electrochem. Soc.

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The oxygen reduction reaction of mixed ionic-electronic conducting (MIEC) cathodes Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) and La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) is investigated by detailed electrochemical impedance spectroscopy and focused ion beam tomography. The oxygen transport parameters of these materials are usually determined for model systems, such as dense bulks or thin films. However in the present study, probable differences regarding the time and thermal history of the samples (e.g. ambient poisoning gases, grain coarsening, secondary phase or surface segregation, etc.) were avoided by the in situ sintering of electrodes with nominal stoichiometry under synthetic air. The microstructural parameters of the electrodes are obtained by 3D FIB-SEM reconstruction tomography and subsequently used in combination with the Adler-Lane-Steele analytical model to calculate a simulated cathode resistance. Large discrepancies are observed compared to the electrochemical impedance measurements. In particular, the electrochemical impedance measurements do not show a Gerischer behavior, as expected for MIEC materials controlled by a coupled surface-exchange and bulk diffusion. Analysis by distribution function of relaxation times (DRT) reveals four individual processes taking place, indicating a surface-exchange controlled behavior with a reaction zone similar to the particle size. Bulk diffusion (D) and surface-exchange (k) coefficients from literature are critically discussed and tentative surface-exchange coefficients (k) for both MIECs are given. High-temperature devices such as solid oxide fuel cells (SOFCs) and oxygen transport membranes (OTMs) are promising systems for working towards zero-emissions power generation. The selected materials require high chemical and microstructural stability, as well as high catalytic activity during the oxygen reduction reaction (ORR), under normal operational conditions (i.e. operational temperature and oxygen partial pressure). Particularly interesting are the mixed ionic-electronic conducting (MIEC) materials, based on the ABO 3 perovskite structure. Their material properties can be flexibly customized, giving solid solutions with high ionic-electronic conductivity and hence good transport properties. More specifically, La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) has become established as the stateof-the-art SOFC cathode, while Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) has presented outstanding oxygen permeation flux in its cubic phase. 1-3The surface-exchange coefficient (k) and the oxygen diffusion coefficient (D) provide key information about the oxygen transport mechanism that dominates the cathodic ORR. Many publications have assessed the D and k values of MIEC materials, most commonly by; electrical conductivity relaxation (ECR) measurements for dense bulks [4][5][6][7][8] and temperature for LSCF cathodes. 17 Here it should be pointed out that the well-known ALS model can only be applied if the measured impedance shows a Gerischer impedance, which indicates tha...

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Section: Resultsmentioning

confidence: 99%

“…[25][26][27] The microstructural parameters of the LSCF cathode were obtained by a linear approximation of the FIB-SEM tomography reconstructed microstructure data of cathodes sintered at 960…”

Section: Methodsmentioning

confidence: 99%

Oxygen Transport Kinetics of Mixed Ionic-Electronic Conductors by Coupling Focused Ion Beam Tomography and Electrochemical Impedance Spectroscopy

Almar

Szász

Weber

et al. 2017

J. Electrochem. Soc.

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“…Extensive simulation work in the field of electrochemical devices using a similar approach as presented above has been carried out by Ivers-Tiffée and co-workers: initially based on COMSOL Multiphysics, the group developed the 3D finite element tool ParCell3D to model the behaviour of fuel cells [136][137][138][139] and batteries. 140 Joos et al 141 used this tool to investigate the representative volume element of tortuosity of an SOFC cathode for both phases, namely the pore and the mixed ionic-electronic conducting LSCF phase.…”

Section: Mesh Based Calculation Methodsmentioning

confidence: 99%

Tortuosity in electrochemical devices: a review of calculation approaches

Tjaden

Brett

Shearing

2016

International Materials Reviews

192

188

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The tortuosity of a structure plays a vital role in the transport of mass and charge in electrochemical devices. Concentration polarisation losses at high current densities are caused by mass transport limitations and are thus a function of microstructural characteristics. As tortuosity is notoriously difficult to ascertain, a wide and diverse range of methods has been developed to extract the tortuosity of a structure. These methods differ significantly in terms of calculation approach and data preparation techniques. Here, we review tortuosity calculation procedures applied in the field of electrochemical devices to better understand the resulting values presented in the literature. Visible differences between calculation methods are observed, especially when using porosity-tortuosity relationships and when comparing geometric and flux based tortuosity calculation approaches.

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“…The size of the sample image is 44.8 × 39.2 μm 2 that corresponds to 80 × 70 pixels. To generate a binary matrix from a raw data set, a simple threshold method could be applied on the raw data by a local minimum of the intensity histogram [26,27]. As shown in Figure 1d, since the intensity profile of the sample image does not have a clear phase boundary between pores and anode materials, it is difficult to define a threshold value directly from the raw image.…”

Section: Segmentationmentioning

confidence: 99%

Geometric Characteristics of Three Dimensional Reconstructed Anode Electrodes of Lithium Ion Batteries

et al. 2014

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Abstract:The realistic three dimensional (3D) microstructure of lithium ion battery (LIB) electrode plays a key role in studying the effects of inhomogeneous microstructures on the performance of LIBs. However, the complexity of realistic microstructures imposes a significant computational cost on numerical simulation of large size samples. In this work, we used tomographic data obtained for a commercial LIB graphite electrode to evaluate the geometric characteristics of the reconstructed electrode microstructure. Based on the analysis of geometric properties, such as porosity, specific surface area, tortuosity, and pore size distribution, a representative volume element (RVE) that retains the geometric characteristics of the electrode material was obtained for further numerical studies. In this work, X-ray micro-computed tomography (CT) with 0.56 μm resolution was employed to capture the inhomogeneous porous microstructures of LIB anode electrodes. The Sigmoid transform function was employed to convert the initial raw tomographic images to binary images. Moreover, geometric characteristics of an anode electrode after 2400 cycles at the charge/discharge rate of 1 C were compared with those of a new anode electrode to investigate morphological change of the electrode. In general, the cycled electrode shows larger porosity, smaller tortuosity, and similar specific surface area compared to the new electrode. OPEN ACCESSEnergies 2014, 7 2559

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Reconstruction of porous electrodes by FIB/SEM for detailed microstructure modeling

Cited by 169 publications

References 14 publications

Oxygen Transport Kinetics of Mixed Ionic-Electronic Conductors by Coupling Focused Ion Beam Tomography and Electrochemical Impedance Spectroscopy

Oxygen Transport Kinetics of Mixed Ionic-Electronic Conductors by Coupling Focused Ion Beam Tomography and Electrochemical Impedance Spectroscopy

Tortuosity in electrochemical devices: a review of calculation approaches

Geometric Characteristics of Three Dimensional Reconstructed Anode Electrodes of Lithium Ion Batteries

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