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

Trini, Martina; Jørgensen, Peter Stanley; Bentzen, Janet Jonna; Hendriksen, Peter Vang; Chen, Ming

doi:10.1149/2.1281902jes

Cited by 54 publications

(39 citation statements)

References 46 publications

(176 reference statements)

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“…The focus is mainly on the quantifying of the volume fraction and TPB density near the electrolyte and comparison with values toward the bulk of the electrode. Ni depletion by up to 6% compared to the Ni volume fraction in the reference sample was reported after 9000 h in a 25-cell stack operated in steam electrolysis [9]. The decrease in connected TPB was very high, in the range of 60-70%, and higher at the inlet, likely because of higher current density and steam partial pressure.…”

Section: Introductionmentioning

confidence: 91%

Evolution of the Morphology Near Triple-Phase Boundaries in Ni–Yttria Stabilized Zirconia Electrodes Upon Cathodic Polarization

Nakajo

Rinaldi

Caliandro

et al. 2020

Journal of Electrochemical Energy Conversion and Storage

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Microstructural changes in Ni–yttria stabilized zirconia (YSZ) near the YSZ electrolyte were examined by three-dimensional (3D) electron microscopy after electrolysis and fuel cell operation up to 10,700 h and 15,000 h, respectively. The depletion of Ni and three-phase boundaries (TPBs) close to the electrolyte was detected upon cathodic polarization. It corresponded to spatial variations of dihedral angles (θ) at TPBs and Ni surface curvature along the direction perpendicular to the electrolyte, which comport with electrowetting and Zener pinning theory on several aspects. θNi decreased by up to 6 deg next to the electrolyte after electrolysis but remained uniform after fuel cell operation. This is in line with predictions from electrowetting theory with capacitances measured by electrochemical impedance spectroscopy and distribution of relaxation times. The decrease in θNi was concurrent to transition toward concave Ni/pore interfacial shapes and lower genus of the Ni phase, which suggests the pinch-off of Ni ligaments following surface diffusion-controlled Rayleigh instability. The increase in absolute mean curvature near the electrolyte interface is a driving force for outward transport of Ni. The decrease in θYSZ further suggests that TPB lines relocate on YSZ surface features that provide higher Zener pinning force. In contrast, few localized contact losses between Ni and YSZ that can also occur under high cathodic polarization and trigger Ni depletion were detected. The results are expected to advance the understanding of the driving forces that cause Ni depletion near the electrolyte in electrolysis for the design of improved solid oxide cell electrode microstructures.

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Section: Introductionmentioning

confidence: 91%

Evolution of the Morphology Near Triple-Phase Boundaries in Ni–Yttria Stabilized Zirconia Electrodes Upon Cathodic Polarization

Nakajo

Rinaldi

Caliandro

et al. 2020

Journal of Electrochemical Energy Conversion and Storage

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show abstract

“…Given that the present changes are barely beyond measurement errors and are not expected in Ni-YSZ operated as a SOFC electrode, it is unclear whether the Ni depletion is real or is a measurement artifact. Based on prior reports [13], one might expect Ni loss near the electrolyte in the SOEC electrode. The lack of an obvious change in the present experiments may be the result of the much shorter life test times of 1000 h, compared to ∼10 000 h in the prior report.…”

Section: Methodsmentioning

confidence: 96%

“…In addition, degradation has been associated with structural changes observed in the Ni-YSZ fuel electrode and the yttria-stabilized zirconia (YSZ) electrolyte. Depletion of Ni from the Ni-YSZ near the interface with YSZ has been observed [13]. Void formation on YSZ electrolyte grain boundaries has been observed after electrolysis life tests [14][15][16], along with an increase in ohmic resistasnce [16].…”

Section: Introductionmentioning

confidence: 94%

Effect of direct-current operation on the electrochemical performance and structural evolution of Ni-YSZ electrodes

et al. 2019

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The effect of electrolysis operations on Ni-YSZ fuel electrode stability was studied at different current densities and fuel mixtures during 1000 h life tests. For a typical electrolysis mixture of 50% H 2 /50% H 2 O and 0.6 A cm −2 current density, cell ohmic resistance values were reasonably stable and no structural changes occurred. However, for more reducing conditions (97% H 2 /3% H 2 O), increasing the current density above 0.4 A cm −2 increased the ohmic resistance accompanied by significant electrolyte degradation including fracture and void formation at grain boundaries. Numerical analysis was carried out to determine the effective oxygen partial pressure across the electrolyte. The results show that the oxygen partial pressure values at high current density and low steam content may be low enough to reduce zirconia to form a Ni-Zr alloy product, initiating the observed electrolyte structural degradation.

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“…However, it is noteworthy that the Ni network shows a comparatively poor percolation (90%), which makes electrical breakdown likely during extended operation at high temperatures by Ni grain coarsening. Poor Ni percolation goes along with a large tortuosity which is considerable higher compared to other cell designs [14,35,36]. In a forthcoming publication, the parameters in Table 3 will be used to model the electrochemical performance of the cell.…”

Section: Correlative Fib-sem Reconstruction With Optimized Parametersmentioning

confidence: 99%

Optimization of Material Contrast for Efficient FIB‐SEM Tomography of Solid Oxide Fuel Cells

et al. 2020

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Focused ion beam (FIB)-scanning electron microscopy (SEM) serial sectioning tomography has become an important tool for three-dimensional microstructure reconstruction of solid oxide fuel cells (SOFC) to obtain an understanding of fabrication-related effects and SOFC performance. By sequential FIB milling and SEM imaging a stack of cross-section images across all functional SOFC layers was generated covering a large volume of 3.5Á10 4 μm 3. One crucial step is image segmentation where regions with different image intensities are assigned to different material phases within the SOFC. To analyze all relevant SOFC materials, it was up to now mandatory to acquire several images by scanning the same region with different imaging parameters because sufficient material contrast could otherwise not be achieved. In this work we obtained high-contast SEM images from a single scan to reconstract all functional SOFC layers consisting of a Ni/Y 2 O 3-doped ZrO 2 (YDZ) cermet anode, YDZ electrolyte and (La,Sr)MnO 3 /YDZ cathode. This was possible by using different, simultaneous read-out detectors installed in a stateof-the-art scanning electron microscope. In addition, we used a deterministic approach for the optimization of imaging parameters by employing Monte Carlo simulations rather than trial-and-error tests. We also studied the effect of detection geometry, detecting angle range and detector type.

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

Cited by 54 publications

References 46 publications

Evolution of the Morphology Near Triple-Phase Boundaries in Ni–Yttria Stabilized Zirconia Electrodes Upon Cathodic Polarization

Evolution of the Morphology Near Triple-Phase Boundaries in Ni–Yttria Stabilized Zirconia Electrodes Upon Cathodic Polarization

Effect of direct-current operation on the electrochemical performance and structural evolution of Ni-YSZ electrodes

Optimization of Material Contrast for Efficient FIB‐SEM Tomography of Solid Oxide Fuel Cells

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