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Title: ELECTROCHEMISTRY AND ON-CELL REFORMATION MODELING FOR SOLID OXIDE FUEL CELL STACKS

Abstract

ABSTRACT Providing adequate and efficient cooling schemes for solid-oxide-fuel-cell (SOFC) stacks continues to be a challenge coincident with the development of larger, more powerful stacks. The endothermic steam-methane reformation reaction can provide cooling and improved system efficiency when performed directly on the electrochemically active anode. Rapid kinetics of the endothermic reaction typically causes a localized temperature depression on the anode near the fuel inlet. It is desirable to extend the endothermic effect over more of the cell area and mitigate the associated differences in temperature on the cell to alleviate subsequent thermal stresses. In this study, modeling tools validated for the prediction of fuel use, on-cell methane reforming, and the distribution of temperature within SOFC stacks, are employed to provide direction for modifying the catalytic activity of anode materials to control the methane conversion rate. Improvements in thermal management that can be achieved through on-cell reforming is predicted and discussed. Two operating scenarios are considered: one in which the methane fuel is fully pre-reformed, and another in which a substantial percentage of the methane is reformed on-cell. For the latter, a range of catalytic activity is considered and the predicted thermal effects on the cell are presented. Simulations of themore » cell electrochemical and thermal performance with and without on-cell reforming, including structural analyses, show a substantial decrease in thermal stresses for an on-cell reforming case with slowed methane conversion.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
947934
Report Number(s):
PNNL-SA-47970
AA2530000; TRN: US200905%%316
DOE Contract Number:
AC05-76RL01830
Resource Type:
Conference
Resource Relation:
Conference: Advances in Solid Oxide Fuel Cells II: Ceramic Engineering and Science Proceedings, 27(4):409-418
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 30 DIRECT ENERGY CONVERSION; ANODES; CERAMICS; DISTRIBUTION; EFFICIENCY; ELECTROCHEMISTRY; FORECASTING; KINETICS; MANAGEMENT; METHANE; PERFORMANCE; SIMULATION; SOLID OXIDE FUEL CELLS; TEMPERATURE DEPENDENCE; THERMAL STRESSES; solid; oxide; fuel; cell

Citation Formats

Recknagle, Kurtis P., Jarboe, Daniel T., Johnson, Kenneth I., Korolev, Alexander, Khaleel, Mohammad A., and Singh, Prabhakar. ELECTROCHEMISTRY AND ON-CELL REFORMATION MODELING FOR SOLID OXIDE FUEL CELL STACKS. United States: N. p., 2007. Web. doi:10.1002/9780470291337.
Recknagle, Kurtis P., Jarboe, Daniel T., Johnson, Kenneth I., Korolev, Alexander, Khaleel, Mohammad A., & Singh, Prabhakar. ELECTROCHEMISTRY AND ON-CELL REFORMATION MODELING FOR SOLID OXIDE FUEL CELL STACKS. United States. doi:10.1002/9780470291337.
Recknagle, Kurtis P., Jarboe, Daniel T., Johnson, Kenneth I., Korolev, Alexander, Khaleel, Mohammad A., and Singh, Prabhakar. Tue . "ELECTROCHEMISTRY AND ON-CELL REFORMATION MODELING FOR SOLID OXIDE FUEL CELL STACKS". United States. doi:10.1002/9780470291337.
@article{osti_947934,
title = {ELECTROCHEMISTRY AND ON-CELL REFORMATION MODELING FOR SOLID OXIDE FUEL CELL STACKS},
author = {Recknagle, Kurtis P. and Jarboe, Daniel T. and Johnson, Kenneth I. and Korolev, Alexander and Khaleel, Mohammad A. and Singh, Prabhakar},
abstractNote = {ABSTRACT Providing adequate and efficient cooling schemes for solid-oxide-fuel-cell (SOFC) stacks continues to be a challenge coincident with the development of larger, more powerful stacks. The endothermic steam-methane reformation reaction can provide cooling and improved system efficiency when performed directly on the electrochemically active anode. Rapid kinetics of the endothermic reaction typically causes a localized temperature depression on the anode near the fuel inlet. It is desirable to extend the endothermic effect over more of the cell area and mitigate the associated differences in temperature on the cell to alleviate subsequent thermal stresses. In this study, modeling tools validated for the prediction of fuel use, on-cell methane reforming, and the distribution of temperature within SOFC stacks, are employed to provide direction for modifying the catalytic activity of anode materials to control the methane conversion rate. Improvements in thermal management that can be achieved through on-cell reforming is predicted and discussed. Two operating scenarios are considered: one in which the methane fuel is fully pre-reformed, and another in which a substantial percentage of the methane is reformed on-cell. For the latter, a range of catalytic activity is considered and the predicted thermal effects on the cell are presented. Simulations of the cell electrochemical and thermal performance with and without on-cell reforming, including structural analyses, show a substantial decrease in thermal stresses for an on-cell reforming case with slowed methane conversion.},
doi = {10.1002/9780470291337},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jan 16 00:00:00 EST 2007},
month = {Tue Jan 16 00:00:00 EST 2007}
}

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  • This paper examines the electrochemical and on-cell steam-methane reforming performance of the solid oxide fuel cell when subjected to pressurization. Pressurized operation boosts the Nernst potential and decreases the activation polarization, both of which serve to increase cell voltage and power while lowering the heat load and operating temperature. A model considering the activation polarization in both the fuel and air electrodes was adopted to address this effect on the electrochemical performance. Both the increase in methane conversion kinetics and the increase in equilibrium methane concentration, which are competing effects of pressurization on steam-methane reforming, are considered in a newmore » rate expression. The models were then applied in simulations to preview how the distributions of reforming rate, temperature, and current density can potentially be changed within stacks operating at elevated pressure. A generic 10 cm counter-flow stack model was created and used for the simulations of pressurized operation. The predictions showed improved thermal and electrical performance with increased operating pressure. The average and maximum cell temperatures decreased by 3% while the cell voltage increased by 9% as the operating pressure was increased from 1 to 10 atmospheres.« less
  • This paper examines the electrochemical and direct internal steam-methane reforming performance of the solid oxide fuel cell when subjected to pressurization. Pressurized operation boosts the Nernst potential and decreases the activation polarization, both of which serve to increase cell voltage and power while lowering the heat load and operating temperature. A model considering the activation polarization in both the fuel and air electrodes was adopted to address this effect on the electrochemical performance. The pressurized methane conversion kinetics and the increase in equilibrium methane concentration are considered in a new rate expression. The models were then applied in simulations tomore » predict how the distributions of direct internal reforming rate, temperature, and current density are effected within stacks operating at elevated pressure. A generic 10 cm counter-flow stack model was created and used for the simulations of pressurized operation. The predictions showed improved thermal and electrical performance with increased operating pressure. The average and maximum cell temperatures decreased by 3% (20ºC) while the cell voltage increased by 9% as the operating pressure was increased from 1 to 10 atmospheres.« less
  • A two-dimensional numerical model is presented for the efficient computation of the steady-state current density, species concentration, and temperature distributions in planar solid oxide fuel cell stacks. The model reduction techniques, engineering approximations, and numerical procedures used to simulate the stack physics while maintaining adequate computational speed are discussed. The results of the model for benchmark cases with and without on-cell methane reformation are presented with comparisons to results from other research described in the literature. The capabilities, performance, and scalability of the model for the study of large multi-cell stacks are then demonstrated.
  • This presentation discusses the development of reliable methods for sealing solid oxide fuel cell stacks.
  • A cell-level distributed electrochemistry (DEC) modeling tool has been developed to enable prediction of solid oxide fuel cell performance by considering the coupled and spatially varying multi-physics that occur within the tri-layer. The approach calculates the distributed electrochemistry within the electrodes, which includes the charge transfer and electric potential fields, ion transport throughout the tri-layer, and gas distributions within the composite and porous electrodes. The thickness of the electrochemically active regions within the electrodes is calculated along with the distributions of charge transfer. The DEC modeling tool can examine the overall SOFC performance based on electrode microstructural parameters, such asmore » particle size, pore size, porosity factor, electrolyte and electrode phase volume fractions, and triple-phase-boundary length. Recent developments in electrode fabrication methods have lead to increased interest in using graded and nano-structured electrodes to improve the electrochemical performance of SOFCs. This paper demonstrates how the DEC modeling tool can be used to help design novel electrode microstructures by optimizing a graded anode for high electrochemical performance.« less