Reaction of Hydrogen/Water Mixtures on Nickel‐Zirconia Cermet Electrodes: I. DC Polarization Characteristics

Holtappels, Peter; Haart, L.G.J. de; Stimming, Ulrich

doi:10.1149/1.1391816

Cited by 84 publications

(68 citation statements)

References 8 publications

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“…The charge transfer coefficients are assumed to be constant within the discussed temperature range. This assumption is consistent with the experimental data reported by Holtappels et al [29]. Constant temperatures are assumed within the computational domain, and the transport coefficients are approximated to be constant in relation to the model variables.…”

Section: Mathematical Modelsupporting

confidence: 84%

“…It is assumed that in the above presented set of equations the anodic forward charge transfer coefficient α an,fwd = 1.4 and the anodic backward reaction coefficient α an,bcw = 0.6, as was experimentally measured by Holtappels et al [29]. The charge transfer coefficients are assumed to be constant within the discussed temperature range.…”

Section: Mathematical Modelmentioning

confidence: 99%

“…The modification of the hydrogen concentration at the inlet causes very little change in the overall stack performance, which is reflected in the simulation. Charge transfer coefficients are generally thought to remain constant in the discussed temperature range, but some variation is still possible [29]. Some error may stem from the assumption of constant temperature, partial pressure, and current distribution within the entire stack.…”

Section: Model Validationmentioning

confidence: 99%

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A Three-Dimensional Microstructure-Scale Simulation of a Solid Oxide Fuel Cell Anode—The Analysis of Stack Performance Enhancement After a Long-Term Operation

et al. 2019

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In this research, we investigate the connection between an observed enhancement in solid oxide fuel cell stack performance and the evolution of the microstructure of its electrodes. A three dimensional, numerical model is applied to predict the porous ceramic-metal electrode performance on the basis of microstructure morphology. The model features a non-continuous computational domain based on the digital reconstruction obtained using focused ion beam scanning electron microscopy (FIB-SEM) electron nanotomography. The Butler–Volmer equation is used to compute the charge transfer at reaction sites, which are modeled as distinct locally distributed features of the microstructure. Specific material properties are accounted for using interpolated experimental data from the open literature. Mass transport is modeled using the extended Stefan–Maxwell model, which accounts for both the binary, and the Knudsen diffusion phenomena. The simulations are in good agreement with the experimental data, correctly predicting a decrease in total losses for the observed microstructure evolution. The research supports the hypothesis that the performance enhancement was caused by a systematic change in microstructure morphology.

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Section: Mathematical Modelsupporting

confidence: 84%

Section: Mathematical Modelmentioning

confidence: 99%

Section: Model Validationmentioning

confidence: 99%

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A Three-Dimensional Microstructure-Scale Simulation of a Solid Oxide Fuel Cell Anode—The Analysis of Stack Performance Enhancement After a Long-Term Operation

et al. 2019

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“…In SOFC modeling studies, the coefficient is generally assumed to be 0.5 (symmetric Butler-Volmer equation), primarily due to the lack of experimental data [26]. However, detailed electrochemical kinetic studies [26][27][28][29] on Ni pattern anodes or Ni cermet anodes has shown that the charge transfer coefficient can have values different from 0.5. For example, the charge transfer coefficient, α, for hydrogen oxidation on Ni/YSZ anodes was estimated to be 0.6-0.7 by Utz et al [26] and approximately 0.7 by Holtappels et al [29].…”

Section: Governing Equations and Reaction Kineticsmentioning

confidence: 99%

Electrochemical Effectiveness Factors for Butler-Volmer Reaction Kinetics in Active Electrode Layers of Solid Oxide Fuel Cells

Nam¹

2017

J. Electrochem. Sci. Technol

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In this study, a numerical approach is adopted to investigate the effectiveness factors for distributed electrochemical reactions in thin active reaction layers of solid oxide fuel cells (SOFCs), taking into account the Butler-Volmer reaction kinetics. The mathematical equations for the electrochemical reaction and charge conduction process were formulated by assuming that the active reaction layer has a small thickness, homogeneous microstructure, and high effective electronic conductivity. The effectiveness factor is defined as the ratio of the actual reaction rate (or equivalently, current generation rate) in the active reaction layer to the nominal reaction rate. From extensive numerical calculations, the effectiveness factors were obtained for various charge transfer coefficients of 0.3-0.8. These effectiveness data were then fitted to simple correlation equations, and the resulting correlation coefficients are presented along with estimated magnitude of error.

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“…Moreover, even for exclusive H 2 fuel, the anode reaction processes are still a matter of controversy and some reaction models have been proposed. [12][13][14][15][16][17][18][19][20][21] To reveal the reaction process in the Ni-ScSZ anode for hydrocarbon fueled SOFCs, electrochemical measurement and outlet gas analysis were carried out for the H 2 -H 2 O system and hydrocarbons of methane ͑CH 4 ͒, propane ͑C 3 H 8 ͒, n-octane ͑C 8 H 18 ͒, and n-dodecane ͑C 12 H 26 ͒ with S/C = 2.0 for the Ni-ScSZ anode at 1073 K. From results, the following points are discussed: ͑i͒ similarity of anode reaction process between hydrocarbon fuels and H 2 , ͑ii͒ electrochemical anode reaction process, and ͑iii͒ hydrogen producing reaction process.Finally, a simple reaction mechanism is proposed that consistently describes processes in both hydrocarbon fuels and H 2 -fed SOFCs. …”

mentioning

confidence: 99%

Reaction Process in the Ni–ScSZ Anode for Hydrocarbon Fueled SOFCs

Kishimoto

Yamaji

Horita

et al. 2006

J. Electrochem. Soc.

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Hydrocarbon fueled cell reactions, which consist of thermal decomposition, reforming, and CO shift reactions, and electrochemical oxidation in the Ni-ScSZ anode of solid oxide fuel cells, were examined by electrochemical measurements and outlet gas analysis for several hydrocarbon fuels ͑CH 4 , C 3 H 8 , C 8 H 18 , C 12 H 26 ͒. Examinations on the anode potential and its relation to observed outlet gas compositions have revealed that hydrogen molecules were mainly electrochemically oxidized even for hydrocarbon fuels. The electrode conductivities can be well correlated with the water vapor partial pressure for both hydrogen and hydrocarbons. Water vapor produced as a result of the electrochemical oxidation of hydrogen promotes the hydrogen-producing reactions in the vicinity of the electrochemically active site. A large difference in the thermal decomposition of hydrocarbons appeared in the anode potential and also in the maximum fuel utilization between methane and other hydrocarbons. A simple reaction model has been proposed to interpret consistently the electrode reactions as well as the reforming and the CO shift reactions with a focus on the oxygen atoms on Ni surfaces as a catalyst for both the electrode and the reforming reactions.The development of direct hydrocarbon solid oxide fuel cells ͑SOFCs͒ has attracted a great deal of interest in recent years. 1-5 It is well recognized that conventional nickel-yttria-stabilized zirconia ͑Ni-YSZ͒ cermet anode degrades with carbon deposition caused by thermal decomposition of hydrocarbon fuels. 1,6 Even so, stable operations of direct hydrocarbon SOFCs were attempted with Niscandia stabilized zirconia ͑ScSZ͒ cermet anode with relative success. Ukai et al. have reported that Ni-ScSZ cermet anodes exhibit higher stability and lower anodic overpotential than the conventional Ni-YSZ anode for methane at a very low steam-to-carbon ratio ͑S/C͒. 7,8 Furthermore, we also have reported that the Ni-ScSZ anode can be used for higher hydrocarbon fuels under carefully selected operation conditions. 9-11 Particularly, a high fuel utilization ͑U f ͒ and a high S/C were essentially important to achieve stable operation and to avoid degradation of the Ni-ScSZ anode and the Ni current collector. However, it has not been fully clarified yet why the anode performance is improved by using ScSZ as the oxide component of the anode. [7][8][9][10][11] It is important to reveal and understand rather complicated reaction processes to improve materials and performance of the anode for direct hydrocarbon SOFCs. When hydrocarbon fuels, especially higher hydrocarbons such as kerosene, are directly fed into the SOFCs, the competition among various reactions makes it difficult to reveal the reaction process. Many kinds of competing reactions, such as thermal decomposition reaction of hydrocarbons, steam reforming reaction, and CO shift reaction, as well as electrochemical oxidation, occur inside the anode at the same time. Moreover, even for exclusive H 2 fuel, the anode reaction processes are sti...

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Reaction of Hydrogen/Water Mixtures on Nickel‐Zirconia Cermet Electrodes: I. DC Polarization Characteristics

Cited by 84 publications

References 8 publications

A Three-Dimensional Microstructure-Scale Simulation of a Solid Oxide Fuel Cell Anode—The Analysis of Stack Performance Enhancement After a Long-Term Operation

A Three-Dimensional Microstructure-Scale Simulation of a Solid Oxide Fuel Cell Anode—The Analysis of Stack Performance Enhancement After a Long-Term Operation

Electrochemical Effectiveness Factors for Butler-Volmer Reaction Kinetics in Active Electrode Layers of Solid Oxide Fuel Cells

Reaction Process in the Ni–ScSZ Anode for Hydrocarbon Fueled SOFCs

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