Electrochemical Characterization of Ni/ScYSZ Electrodes as SOFC Anodes

Ramos, Tânia; Søgaard, Martin; Mogensen, Mogens Bjerg

doi:10.1149/2.045404jes

Cited by 57 publications

(53 citation statements)

References 33 publications

(60 reference statements)

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“…42 The variation in percolating TPB density was thus separated from the variation in active area fraction as shown in Figure 16. The TPB density was then estimated from the model using the values for the exchange current density per unit length of TPB and the effective ionic …”

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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“…2c), which was previously shown to be gas diffusion in the thick porous support layer. 32 The SWE Ni-ScYSZ electrode impedance has no such lowfrequency process, illustrating that the gas diffusion resistance is minimized in this porous electrode geometry. For both electrodes, the C : H R p ratio is 2, suggesting a conrmation of previous reports that the use of ScYSZ does not change the 3PB reaction mechanism compared with YSZ.…”

Section: Impedance Spectroscopymentioning

confidence: 97%

“…The porous Ni-SZ electrodes gave a typical Gerischer-like porous electrode impedance response, 32,43,44 with skewed semicircles that lean the opposite way compared to the model Ni/YSZ electrode ( Fig. 2c and d).…”

Section: Impedance Spectroscopymentioning

confidence: 97%

Kinetics of CO/CO₂ and H₂/H₂O reactions at Ni-based and ceria-based solid-oxide-cell electrodes

2015

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Document Version Peer reviewed version Link back to DTU Orbit Citation (APA):Graves, C. R., Chatzichristodoulou, C., & Mogensen, M. B. (2015). Kinetics of CO/CO2 and H2/H2O reactions at Ni-based and ceria-based solid-oxide-cell electrodes. Faraday Discussions, 182, Comparing model and porous Ni-SZ electrodes, the ratio of electrode polarization resistance in CO/CO 2 vs. H 2 /H 2 O decreases from 33 to 2. Experiments and modelling suggest that the ratio decreases due to a lower concentration of impurities blocking the three phase boundary and due to the nature of the reaction zone extension into the porous electrode thickness. Besides showing higher activity for H 2 /H 2 O reactions than CO/CO 2 reactions, the Ni/SZ interface is more active for oxidation than reduction. On the other hand, we find the opposite behaviour in both cases for CGOn/STN model electrodes, reporting for the first time a higher electrocatalytic activity of CGO nanoparticles for CO/CO 2 than for H 2 /H 2 O reactions in the absence of gas diffusion limitations. We propose that enhanced surface reduction at the CGOn/gas two phase boundary in CO/CO 2 and in cathodic polarization can explain why the highest reaction rate is obtained for CO 2 electrolysis. For all materials investigated, large differences

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“…pure CGO), ranging from 35.7 kJ/mol to 41.1 kJ/mol. It is noted that a stagnant gas layer on top of the cells in the used test setup causes a rather large contribution to R p (30)(31)(32). This form of gas diffusion resistance is not inherent to the cells, and will artificially enlarge R p .…”

Section: Electrochemical Testingmentioning

confidence: 99%

Carbon and Redox Tolerant Infiltrated Oxide Fuel-Electrodes for Solid Oxide Cells

et al. 2016

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To solve issues of coking and redox instability related to the presence of nickel in typical fuel electrodes in solid oxide cells, Gd-doped CeO 2 (CGO) electrodes were studied using symmetric cells. These electrodes showed high electro-catalytic activity, but low electronic conductivity. When infiltrated with Sr 0.99 Fe 0.75 Mo 0.25 O 3-δ (SFM), the electronic conductivity was enhanced. However, polarization resistance of the cells increased, suggesting that the infiltrated material is less electro-catalytically active and was partly blocking the CGO surface reaction sites. The activity could be regained by infiltrating nano-sized CGO or NiCGO on top of SFM, while still sustaining the high electronic conductivity. Ohmic resistance of the electrodes was thus practically eliminated and performance comparable to, or better than, state-of-the-art fuel electrodes was achieved. The Ni containing cells were damaged by carbon deposition in a CO/CO 2 -atmosphere, while none of the non-nickel cells catalyzed carbon. Stability towards redox cycles was also proven.

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Electrochemical Characterization of Ni/ScYSZ Electrodes as SOFC Anodes

Cited by 57 publications

References 33 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

Kinetics of CO/CO₂ and H₂/H₂O reactions at Ni-based and ceria-based solid-oxide-cell electrodes

Carbon and Redox Tolerant Infiltrated Oxide Fuel-Electrodes for Solid Oxide Cells

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