Three-Dimensional Microstructural Evolution of Ni- Yttria-Stabilized Zirconia Solid Oxide Fuel Cell Anodes At Elevated Temperatures

Kennouche, David; Chen-Wiegart, Yu Chen Karen; Cronin, J. Scott; Wang, Jun; Barnett, Scott A.

doi:10.1149/2.084311jes

Cited by 58 publications

(82 citation statements)

References 36 publications

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“…32,34,35 The process at 10 2 -10 3 Hz was assigned to the electrochemical anodic reaction. [36][37][38][39] The large low frequency response at 1-10 Hz is most likely a gas conversion impedance due to the test rig geometry, and is caused by diffusion of gas molecules from the flowing gas stream into, and out of, the electrode compartments of the cell test chamber. 40,41 The different contributions are shown as an equivalent circuit model in the inset and their assignments are discussed later.…”

Section: Resultsmentioning

confidence: 99%

Characterization of Degradation in Nickel Impregnated Scandia-Stabilize Zirconia Electrodes during Isothermal Annealing

Chen

Bertei

Ruiz‐Trejo

et al. 2017

J. Electrochem. Soc.

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This study investigates the stability of nickel-impregnated scandia-stabilize zirconia composite electrodes during isothermal annealing at temperatures from 600 to 950 • C in a humidified hydrogen atmosphere (3 vol % water vapor). Typically an initial rapid degradation of the electrode during the first 17 h of annealing is revealed by both an increase in polarization resistance and a fall in electronic conductivity. Secondary electron images show a shift in nickel particle size toward larger values after 50 h of annealing. The declining electrochemical performance is hence attributed to nickel coarsening at elevated temperatures. Nickel coarsening has two microstructural effects: breaking up nickel percolation; and reducing the density of triple phase boundaries. Their impact on electrode area specific resistance is explored using a physical model of electrode performance which relates the macroscopic electrochemical performance to measurable microstructural parameters. The solid oxide fuel cell (SOFC) offers both high conversion efficiency and low environmental pollution.1 When combined with a bottoming gas turbine generator, the resulting hybrid (SOFC-GT) system is capable of reaching 70% electrical efficiency.2,3 The typical operational temperature for an SOFC is in the range of 600• C to 1000 • C, depending on the design and the materials employed. Such high temperature operation makes it possible to use not only hydrogen, but also reformed hydrocarbon fuels, or even unreformed hydrocarbons (direct operation) if nickel-free anodes are employed.4,5 By recovering the waste heat, SOFCs can be used as a combined heat and power (CHP) unit with high electrical and total efficiencies. 6,7 At the SOFC anode, gaseous fuel molecules are oxidized by the oxide ions O 2− transported through the electrolyte, giving out electrons to an external circuit.8 Nickel-yttria-stabilize-zirconia (YSZ) cermet is the most widely-used SOFC anode material due to its low thermal expansion coefficient mismatch with the electrolyte 9 and the high electro-catalytic activity of nickel.10,11 8 mol% YSZ has an oxygen ionic conductivity of 0.164 S cm −1 at a temperature of 1000• C. 12 In comparison, 12 mol% scandia-stabilize-zirconia (ScSZ) has a higher conductivity of 0.300 S cm −1 at 1000 • C 13 and is preferable to YSZ for SOFCs working in the lower range of SOFC operating temperatures. 14,15 Conventionally nickel-based anodes are fabricated by mixing powders of NiO and the chosen ionic conductor and then reducing the NiO to Ni on first use of the cell. However, impregnation of a soluble nickel salt into a preformed ionically conducting porous skeleton has been investigated as an alternative fabrication technique because it gives a finer dispersion of Ni particles on reduction. 16,17 This has also been shown to be more redox stable.18 Impregnation has been shown to produce electrodes with superior electrochemical performance compared to the conventional route. For example, impregnating La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-d (LSGM) with nickel pr...

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Section: Resultsmentioning

confidence: 99%

Characterization of Degradation in Nickel Impregnated Scandia-Stabilize Zirconia Electrodes during Isothermal Annealing

Chen

Bertei

Ruiz‐Trejo

et al. 2017

J. Electrochem. Soc.

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“…12,14 Fig. The AFLs red at different temperatures were explored by using three-dimensional tomography.…”

Section: Resultsmentioning

confidence: 99%

“…The substantial decrease in the EIS response at $5 Hz in Fig. 14,29,32 The larger pores in the images, which resulted from the starch pore former used in the support formulation, are all black, i.e., percolated. 14 The large size of the pores in the Ni-YSZ anode support makes it difficult to quantitatively characterize the 3D structure using FIB-SEM, which can sample only a limited volume.…”

Section: 14mentioning

confidence: 96%

Solid oxide cells with zirconia/ceria Bi-Layer electrolytes fabricated by reduced temperature firing

et al. 2015

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Anode-supported solid oxide cells (SOCs) with thin bi-layer Y 0.16 Zr 0.92 O 2Àd (YSZ)/Gd 0.1 Ce 0.9 O 1.95 (GDC) electrolytes were prepared by a reduced-temperature (1250 C) co-firing process enabled by the addition of a Fe 2 O 3 sintering aid. The Fe 2 O 3 amounts in the layers affected the formation of voids at the GDC/YSZ interface; the case with 1 mol% Fe 2 O 3 in the YSZ layer and 2 mol% Fe 2 O 3 in the GDC layer yielded minimal interfacial voids, presumably because of optimized shrinkage matching between the electrolyte layers during co-firing. The best cells yield fuel cell power density at 0.7 V in air and humidified hydrogen of 1.74 W cm À2 (800 C) and 1.0 W cm À2 (700 C). Under electrolysis conditions, i.e., air and 50 vol% H 2 O-50 vol% H 2 , the best cell area specific resistance is 0.12 U cm 2 at 800 C and 0.27 U cm 2 at 700 C. This excellent cell performance was explained by a number of factors related to the reduced firing temperature: (1) low electrolyte resistance due to minimization of YSZ/GDC interdiffusion; (2) minimal zirconate phase formation between the YSZ and the La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3 (LSFC) cathode because of the dense GDC barrier layer; (3) high three phase boundary density in the Ni-YSZ anode functional layer; and (4) good pore connectivity in the Ni-YSZ support. Preliminary life testing under fuel cell and electrolysis operation shows promising cell stability.

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“…Moreover, the agglomeration behavior of the Ni particles and the resulting performance loss of the Ni cermet anodes are dependent on various factors such as anode fabrication process, particle size distributions of Ni and ion-conducting phase, and cell operating parameters. 41,42 It is possible that these factors also played a favorable role in maintaining stable cell performance in the present study. Nevertheless, additional tests at different temperatures with longer operating times would be desirable to confirm and further elucidate the stability of anode and anode current collector layers in the present micro-tubular design.…”

Section: Resultsmentioning

confidence: 81%

Fabrication and Evaluation of a Micro-Tubular Solid Oxide Fuel Cell with an Inert Support Using Scandia-Stabilized Zirconia Electrolyte

Panthi

Choi

Tsutsumi

2015

J. Electrochem. Soc.

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We have proposed a novel micro-tubular solid oxide fuel cell (SOFC) design with an inert support and an integrated current collector for the inner electrode to improve current collection efficiency as well as reduction-oxidation stability of the cell. In this work, a micro-tubular SOFC based on the proposed design was fabricated using scandia-stabilized zirconia (ScSZ) as electrolyte owing to its high ionic conductivity over a wide range of temperatures. Yttria-stabilized zirconia (YSZ), Ni, Ni-ScSZ, strontium-doped lanthanum manganite (LSM)-ScSZ, and LSM were used as the inert support, anode current collector, anode, cathode, and cathode current collector, respectively. The electrochemical performance of the fabricated cell was evaluated at temperatures between 600 and 850 • C. Because of the lower ohmic resistance across its components, the cell exhibited good power generation performance at high and intermediate temperatures. Solid oxide fuel cells (SOFCs) are high-temperature electrochemical energy conversion devices that have attracted increased attention in recent decades owing to their high power generation efficiency and environmentally benign operation.1,2 In contrast with low-temperature fuel cells such as polymer electrolyte membrane fuel cells (PEMFCs) and alkaline fuel cells (AFCs), SOFCs can be operated with both hydrogen and hydrocarbon fuels, and they are also tolerant toward several fuel contaminants.3-5 Additionally, the high-quality exhaust heat obtained from SOFCs can be used for combined cycle and cogeneration applications, which increases the system efficiency significantly. [6][7][8] Among different SOFC designs, the micro-tubular design possesses some unique characteristics. By combining the merits of a tubular geometry and smaller size, micro-tubular SOFCs offer easy sealing, high volumetric power density, good thermo-cycling behavior, and high thermal shock resistance. 1,9 Owing to their ability for rapid startup and shutdown, micro-tubular SOFCs have gained considerable interest for their use in mobile applications in addition to the traditionally considered stationary applications. 10,11 However, one of the major problems with conventional micro-tubular SOFCs is their poor current collection efficiency. 12,13 This problem arises from the small cell diameter that prevents the use of current-collecting elements such as wires and meshes to collect current from the entire inner electrode surface. As a result, current-collecting elements have to be applied to the exposed end(s) of the inner electrode, which increases the current conduction path and thus the ohmic resistance. This limits active cell length to few centimeters or less so as to keep the ohmic resistance in the cell within an acceptable range.12 In addition, stability of the cell performance under reduction-oxidation (redox) cycling conditions is a crucial issue for conventional micro-tubular SOFCs that contain state-of-the-art Ni-yttria-stabilized zirconia (YSZ) anode supports.14-16 Ni particles in the anode support may oxidiz...

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Three-Dimensional Microstructural Evolution of Ni- Yttria-Stabilized Zirconia Solid Oxide Fuel Cell Anodes At Elevated Temperatures

Cited by 58 publications

References 36 publications

Characterization of Degradation in Nickel Impregnated Scandia-Stabilize Zirconia Electrodes during Isothermal Annealing

Characterization of Degradation in Nickel Impregnated Scandia-Stabilize Zirconia Electrodes during Isothermal Annealing

Solid oxide cells with zirconia/ceria Bi-Layer electrolytes fabricated by reduced temperature firing

Fabrication and Evaluation of a Micro-Tubular Solid Oxide Fuel Cell with an Inert Support Using Scandia-Stabilized Zirconia Electrolyte

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