fundamental physics and chemistry of direct ... · • couple elementary thermal chemistry and...
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![Page 1: Fundamental Physics and Chemistry of Direct ... · • Couple elementary thermal chemistry and electrochemistry • Determine the chemical routes to deposit formation • Bridge scales](https://reader034.vdocument.in/reader034/viewer/2022042621/5f7007d79731896d5b01e1d1/html5/thumbnails/1.jpg)
Seca_Asilomar_42/05.p1
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Fundamental physics and chemistry of direct electrochemical oxidation in SOFC
Robert J. Kee, Anthony M. Dean, and Mark T. LuskColorado School of Mines
David G. Goodwin, Sossina M. Haile, and William A. Goddard, IIICalifornia Institute of Technology
Gregory S. Jackson, Robert A. Walker, and Bryan W. EichhornUniversity of Maryland, College Park
[email protected] (303) 273-3379
Presented:SECA Workshop
Asilomar, CAApril 20, 2005
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Seca_Asilomar_42/05.p2
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
The MURI research seeks to understand the chemical fundamentals of DECO
Important fundamental issues• Establish elementary kinetics of charge-transfer processes• Establish elementary kinetics of internal reforming and partial oxidation• Couple elementary thermal chemistry and electrochemistry• Determine the chemical routes to deposit formation• Bridge scales (atomic to fluid flow) to predict cell-level performance
Technical approach• Develop and apply predictive models across length scales• Devise and operate experiments that illuminate particular processes• Use focused experiments to inform, guide, and validate modeling• Use modeling to help focus and interpret experimentation
Overall objectives• Develop and validate advanced modeling tools• Assist the optimal design and development of fuel-cell architectures
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Seca_Asilomar_42/05.p3
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Concerted theory and experimentation work to improve understanding the fundamentals
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Seca_Asilomar_42/05.p4
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Molecular dynamics assists understanding surface chemistry and transport
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Seca_Asilomar_42/05.p5
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Surface diffusivities are derived from molecular-dynamics simulations
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Seca_Asilomar_42/05.p6
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Pattern anodes are an important vehicle to establish the charge-transfer chemistry
Electrochemical performance• Voltage-current characterization• Impedance spectroscopy
Surface interrogation• Micro-Raman spectroscopy
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Seca_Asilomar_42/05.p7
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Pattern anode experiments provide polarization and impedance data
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Seca_Asilomar_42/05.p8
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Deposit formation affects pattern-anode cell performance significantly
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Seca_Asilomar_42/05.p9
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
UMCP’s optically accessible anode provides a means to interrogate surface chemistry
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Seca_Asilomar_42/05.p10
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Samaria-doped ceria (SDC15) is characterized with impedance spectroscopy
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Seca_Asilomar_42/05.p11
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Hydrogen electro-oxidation appears to occur on the ceria surface
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Seca_Asilomar_42/05.p12
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
MD simulations reveal the role of different metals in catalyzing carbon growth
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Seca_Asilomar_42/05.p13
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Homogeneous chemistry models predict observed fuel conversion and deposits
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Seca_Asilomar_42/05.p14
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Gas-phase kinetics transforms the fuel as a function of composition and residence time
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Seca_Asilomar_42/05.p15
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Molecular-weight chemistry is a perturbation on heterogeneous and electrochemistry
Solve dual-channel model• Neglect gas-phase chemistry• Simple gas-phase chemistry• Include heterogeneous chemistry• Include electrochemistry
Evaluate fluxes to/from channel
Elementary gas-phase chemistry• Modified plug flow• Imposed wall fluxes• Predict molecular-weight growth
Large mechanism~ 2500 reactions ~ 300 species
Combustion• Soot models
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Seca_Asilomar_42/05.p16
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Cell structure and operation affect the gas-phase molecular-weight growth
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Seca_Asilomar_42/05.p17
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
The models incorporate elementary charge-transfer chemistry
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Seca_Asilomar_42/05.p18
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Goodwin’s pattern-anode model is the first of its kind
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Seca_Asilomar_42/05.p19
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Performance is predicted from elementary chemistry and thermodynamics
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Seca_Asilomar_42/05.p20
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
What is the role of the anode structure in promoting reforming, shifting, and CPOX
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Seca_Asilomar_42/05.p21
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
MEA models do a good job of representing measured electrochemical performance
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Seca_Asilomar_42/05.p22
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
The Dusty-Gas model applies when the mean-free path is comparable to the pore size
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Seca_Asilomar_42/05.p23
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
The models accommodate elementary heterogeneous reforming/CPOX chemistry
Collaboration with Olaf Deutschmann, University of Karlsruhe
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Seca_Asilomar_42/05.p24
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
The separated-anode experiment is designed to isolate thermal heterogeneous chemistry
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Seca_Asilomar_42/05.p25
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Dry reforming (CO2) is nearly as effective as steam reforming
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Seca_Asilomar_42/05.p26
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Our models incorporate coupled fluid flow, thermal chemistry, and electrochemistry
ApproachReactive flowPorous-media transportHomogeneous chemistryHeterogeneous chemistryElectrochemistry
PerformanceEfficiencyUtilizationPower density
OperationCell voltageFlow ratesFuel mixtures
DesignMEA architectureCatalyst materialsElectrode microstructure
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Seca_Asilomar_42/05.p27
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
The models predict composition along the channels and through the electrodes
Anode lnlet: 66% H2, 22% CO, 12% CH4, 30 cm/s, 800˚C, 1 atm.Cathode: Air
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Seca_Asilomar_42/05.p28
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Efficiency, utilization, and power density depend greatly on operating voltage
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Seca_Asilomar_42/05.p29
DECO MURI Colorado School of Mines University of Maryland California Institute of Technology
Although understanding is advancing rapidly, much remains to be done
Charge-transfer chemistry• Currently in modified BV form ==> Need elementary mechanisms• Currently consider H2 ==> Need general mixed potential• Limited validation data ==> Need validation data and theory
Reforming and CPOX chemistry• Current models for methane ==> Need higher hydrocarbons • Current models for Ni ==> Consider alternative catalysts• Assume inert ceramic supports ==> Investigate ceramic activity
Cell and electrode optimization• Structure drives performance ==> Functionally grade electrodes• Alternative catalyst function ==> Functionally grade electrodes
Coupling at the stack and system level• Models are for single channel ==> Extend to full cell and stack• Couple to thermal analysis ==> Depends on system boundaries• Models for channels ==> Consider tube or sheet layout