Kinetic Monte Carlo Simulations of Solid Oxide Fuel Cell

Pornprasertsuk, Rojana; Holme, Tim; Prinz, Friedrich

doi:10.1149/1.3232209

Cited by 18 publications

(9 citation statements)

References 59 publications

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“…15 The overall fuel cell reaction H 2 + 1/2 O 2 → H 2 O is broken down into the elementary steps that occur on the cathode and anode; a complete list, including the activation energies of each process, is given in the Appendix.…”

Section: Calculationsmentioning

confidence: 99%

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Interpretation of Low Temperature Solid Oxide Fuel Cell Electrochemical Impedance Spectra

Holme

Pornprasertsuk

Prinz

2010

J. Electrochem. Soc.

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Electrochemical impedance spectroscopy was performed on low temperature solid oxide fuel cells with yttria-stabilized zirconia electrolytes and different electrode materials and morphologies. Three loops are seen in a Nyquist plot; the high frequency loop is attributed to the electrolyte and series resistance. The intermediate and low frequency loops are influenced by the material and morphology of both electrodes. To clarify which elementary processes contribute to each loop, kinetic Monte Carlo simulations of a solid oxide fuel cell were performed to calculate the reaction rates for each elementary process. The rates fall into three groupings, allowing the identification of processes with corresponding features in the impedance spectra. Vacancy diffusion processes occur at the highest frequency, agreeing with the usual assignment of the high frequency loop with series resistance. Chemical reactions at the anode have an intermediate frequency, suggesting that the intermediate frequency loop is dominated by anode reactions. Low frequency reactions include electrochemical reactions, chemical reactions at the cathode, and water formation and desorption at the anode. This agrees with the experimental findings of the strong dependence of the low frequency loop on the bias voltage and the dominance of the cathode reactions in the low frequency regime.Solid oxide fuel cells ͑SOFCs͒ may potentially deliver power at high efficiency while avoiding issues of water clogging and catalyst poisoning suffered by proton exchange membrane fuel cells. 1 To enable the economic manufacture of SOFC units, efficient operation below 500°C is an active area of research. At low temperatures, the performance of thin-film SOFCs is limited by sluggish electrode reactions, even with relatively highly active platinum electrodes. 2,3 Electrochemical impedance spectroscopy ͑EIS͒ is a widely used tool in investigating the causes of inefficiency in fuel cells under different operating conditions. 4 Despite a wealth of data and analysis of Pt electrodes on yttria-stabilized zirconia ͑YSZ͒ electrolytes, there remains controversy about the assignment of features in an EIS spectra to physical processes. Some authors attribute the cathodic overpotential to the sluggishness of electrochemical reactions, 5,6 while others demonstrate a contribution from concentration effects. 7 Due to the complex interplay of a myriad of reactions occurring simultaneously on fuel cell electrodes, there remains uncertainty about the assignation of overpotentials to reactions, even on model systems such as Pt/YSZ. This work aims to clarify the situation by identifying the features of experimental EIS spectra with elementary physical reactions. Further, most studies have been done on higher temperature systems above 700°C, 8,9 while this work presents a systematic study of lower temperature ͑Ͻ400°C͒ reactions on noble metal electrodes.To facilitate a close study of why platinum electrodes show good performance and to guide the search for replacement materials for platinum, ...

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Section: Calculationsmentioning

confidence: 99%

“…Please refer to Ref. 15 for more KMC simulation details. In this work, the simulation is focused on the impedance response of the SOFC system; therefore, the previous dc SOFC simulation code is modified to allow the ac to be imposed on the fuel cell.…”

Section: Calculationsmentioning

confidence: 99%

Interpretation of Low Temperature Solid Oxide Fuel Cell Electrochemical Impedance Spectra

Holme

Pornprasertsuk

Prinz

2010

J. Electrochem. Soc.

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“…Tests are performed to verify first-order and Arrhenius behavior. Kinetic information collected from MD trajectories can be supplied to kinetic Monte Carlo simulations. − …”

Section: Introductionmentioning

confidence: 99%

Relative Occurrence of Oxygen-Vacancy Pairs in Yttrium-Containing Environments of Y₂O₃-Doped ZrO₂ Can Be Crucial to Ionic Conductivity

Jaipal

Chatterjee

2017

J. Phys. Chem. C

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Yttria-stabilized zirconia (YSZ) is widely used as an electrolyte in solid oxide fuel cells. Much of current research on ionic conductivity in YSZ has focused on understanding migration barriers for O2– ion movement and vacancy trapping behavior in an attempt to understand why dopant cation edges result in fewer vacancy hopping transitions. We show that the free energy of finding O2–-vacancy (O2–-vac) pairs in a local environment can also be crucial to the hopping transitions. Higher probability of O2–-vac pairs can result in a greater number of transitions. O2– ion movement in bulk YSZ is studied here using multiple independent short molecular dynamics (MD) trajectories. Analysis of the MD trajectories yields free energy of O2–-vac pairs in 42 different local cation (Y3+/Zr4+) environments, to our knowledge calculated for the first time, as well as coarse-grained O2– hopping rates and Arrhenius parameters. On the basis of the free energies we conclude that it is possible that ionic movement is hindered in some environments not only because of high migration barriers or vacancy trapping as believed earlier but also because O2–-vac pairs are destabilized by these environments. Increasing the temperature and/or decreasing the dopant composition stabilizes O2–-vac pairs in these environments, which in turn affects the YSZ conductivity. Another newly found aspect is the connection between the kinetic rate constants for different environments; namely, the rates of interconversion between two environments depend on their O2–-vac free energy differences.

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“…The SCF KMC problem has also been solved for a ~80 nm SOFC (24) using the Table data, which are appropriate for the hydrogen spillover anode model. The results are comparable, due to the fact that the rate-limiting reactions are the charge transfer events in both electrodes (20,22,24).…”

Section: Ecs Transactions 35 (1) 1055-1063 (2011)mentioning

confidence: 82%

Self-Consistent-Field Electrochemistry

Gatewood¹,

Turner²,

Dunlap³

2011

ECS Trans.

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Two self-consistent-field Kinetic Monte Carlo (KMC) models are developed to simulate the operating cathode and anode of 9 mol % Yttria Stabilized Zirconia (YSZ) solid oxide fuel cells (SOFCs) using a database of elementary reaction rates obtained from experimental and first-principles rates. The rates are used in the unit cells of two asymmetrical YSZ lattices for the cathode and anode. KMC then gives the current-voltage (I-V) characteristics of this sequential set of elementary chemical reactions. The resistance of a single electrolyte lattice layer added to either simulation cell is extracted by Taylor-series interpolation of the I-V curves for simulation cells of different thickness. Its conductivity is obtained from this resistance using the cross-sectional area of the simulation cells. These conductivities are compared to experiment and a statistically independent model of this set of chemical reactions.

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Kinetic Monte Carlo Simulations of Solid Oxide Fuel Cell

Cited by 18 publications

References 59 publications

Interpretation of Low Temperature Solid Oxide Fuel Cell Electrochemical Impedance Spectra

Interpretation of Low Temperature Solid Oxide Fuel Cell Electrochemical Impedance Spectra

Relative Occurrence of Oxygen-Vacancy Pairs in Yttrium-Containing Environments of Y₂O₃-Doped ZrO₂ Can Be Crucial to Ionic Conductivity

Self-Consistent-Field Electrochemistry

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Kinetic Monte Carlo Simulations of Solid Oxide Fuel Cell

Cited by 18 publications

References 59 publications

Interpretation of Low Temperature Solid Oxide Fuel Cell Electrochemical Impedance Spectra

Interpretation of Low Temperature Solid Oxide Fuel Cell Electrochemical Impedance Spectra

Relative Occurrence of Oxygen-Vacancy Pairs in Yttrium-Containing Environments of Y2O3-Doped ZrO2 Can Be Crucial to Ionic Conductivity

Self-Consistent-Field Electrochemistry

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Relative Occurrence of Oxygen-Vacancy Pairs in Yttrium-Containing Environments of Y₂O₃-Doped ZrO₂ Can Be Crucial to Ionic Conductivity