SECA Core Technology Program

The Solid State Energy Conversion Alliance SECA Core Technology Program Third Annual SECA Workshop March 21-22, 2002 Washington, D.C. Wayne A. Surdoval SECA Program Coordinator www.netl.doe.gov/scng U.S. Department of Energy Pacific Northwest National Laboratory 1 SECA Core Technology Program Solicitation • Fuel Processing − Contaminant Resistant Anodes and Reforming Catalysts for Intermediate Temperature Solid Oxide Fuel Cell Systems − High Temperature Sulfur Removal • • Manufacturing − Low Cost Production of Precursor Materials Controls and Diagnostics − Sensors − Active Sealing Systems • Power Electronics − Interaction Between Fuel Cell, Power Conditioning Systems and Application Loads − DC-to-DC Converters for Solid-Oxide Fuel Cells • Modeling & Simulation − Fuel Cell Failure Analysis − Manufacturing Models • Materials − Cathodes − Interconnects − Innovative Sealing Concepts U.S. Department of Energy Pacific Northwest National Laboratory Descriptor - include initials, /org#/date 2 SECA Core Technology Program Activities at PNNL U.S. Department of Energy Pacific Northwest National Laboratory 3 Core Technology - Areas of Emphasis • SOFC component development • Anode Supported Cell Fabrication & Performance Optimization • Tape casting process • Anode & cathode materials • Interconnects • Seals • SOFC modeling • Modeling of cells and stacks – transient and steady state • System modeling U.S. Department of Energy Pacific Northwest National Laboratory 4 Advantages of LSF Cathode Oxygen Self Diffusion Coeff. (cm2/s) High oxygen diffusion coefficient (relative to LSM) increases “effective” TPB at the cathode / electrolyte interface, thereby reducing the cathode overpotential 1.00E+00 1.00E-02 1.00E-04 1.00E-06 1.00E-08 1.00E-10 1.00E-12 1.00E-14 1.00E-16 600 LSM-50 LSCo-20 LSCo-10 LSF-10 LSF-40 LCCF-6482 LSCN-6482 LSCF-6428 LSCF-4628 Other advantages of LSF as cathode material: High oxygen surface exchange coefficient; TEC is compatible with other cell components; high electronic conductivity 700 800 900 1000 1100 Temperature (C) Data from PNNL (LSCF compositions) and others (CRC Handbook of Solid State Electrochemistry p. 505) U.S. Department of Energy Pacific Northwest National Laboratory 5 Temperature Dependence of Anode-supported Cell Performance 1.2 1.4 Cell: 1 1.2 0.8 Voltage (V) 0.8 0.6 0.6 0.4 800ºC 750ºC 700ºC 650ºC 0.4 Fuel: 97% H2 / 3% H2O (Low Fuel Utilization) Oxidant: Air 0.2 0.2 0 0 0.5 1 Current Density (A/cm2) 1.5 2 0 U.S. Department of Energy Pacific Northwest National Laboratory 6 Power Density (W/cm2) LSF Cathode / SDC Interlayer / YSZ Electrolyte / Ni-YSZ anode 1 Advanced Red/Ox Tolerant Anode 0.014 0.012 0.01 ∆L/LO 0.008 0.006 0.004 0.002 0 0 5 10 15 20 25 30 35 time (hours) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Simulated Thermal CyclesI: Exposure to reducing environment at 1000ºC (corresponding to SOFC anode environment during operation) II: Exposure to air during thermal cycling (corresponding to conditions an unprotected anode would experience during sytem startup and shutdown) I II I II I U.S. Department of Energy Pacific Northwest National Laboratory 7 Temperature ( oC) Doped SrTiO3 compositions show promise as red-ox tolerant anode materials “Advanced” compressive seal concept In coupon testing, mica gaskets exhibited relatively high leak rates under moderate compressive loads. In recent testing, advanced compressive seals exhibited leak rates approximately 2 orders of magnitude lower relative to simple mica gasket. Test conditions: 800ºC in air le ak ra te , s cc m Simple Mica Seal “Advanced” Seals 10 1 0 .1 0 .01 0 .00 1 0 2 00 4 00 6 00 8 00 1 00 0 1 20 0 a pplie d com pre ss ive loa d, ps i U.S. Department of Energy Pacific Northwest National Laboratory 8 Metallic Interconnect Development 3-step Screening & Testing Study to Evaluate Candidate Alloys s Goals: Identify candidate alloys for SOFC interconnect; Develop understanding of corrosion processes and mechanisms s s Step 1 – completed – compiled metallurgical database; reduced candidate list from ~300 to ~15 alloys Step 2 – in progress – screening tests • chemical – stability in fuel and oxidant environment, compatibility and bonding strength with seal materials • electrical – effects of environment on scale resistance • mechanical – effects of environment on mechanical properties • fabrication – formability and joinability testing U.S. Department of Energy Pacific Northwest National Laboratory 9 Overview of Modeling and Simulations Flow Analysis Modeling levels Electrical Power System Thermal system Flow, thermal & Electrochemistry analysis Temperature profile Thermal Analysis Stack Continuum-level electrochemistry Cell-level Cell Microstructurelevel Computational Tools for Thermal Cycling Stress Analysis Validation and Property measurement Thermal Shock H2O concentration Methane distribution U.S. Department of Energy Pacific Northwest National Laboratory 10 Accomplishments: • Low cost tape casting process for anode & electrolyte fabrication • Single step sintering process for anode-supported electrolyte cosintering • Non-nickel base anode for oxygen tolerance • Sr doped lanthanum ferrite cathode electrode for superior performance • Engineering performance models for cell & stack operations • Data base compilation for candidate metallic current collector U.S. Department of Energy Pacific Northwest National Laboratory 11 NETL SOFC Model Capabilities • Three-dimensional, steady-state, with fluid dynamics, heat transfer, species transport, chemical reaction, porous media flow − Water-gas shift reaction − Species diffusion in flow channels and porous media • Electrochemical SOFC submodel − − 3H 2 + 3O 2 ⇒ 3H 2O + 6e − − CO + O 2 ⇒ CO2 + 2e − − 2O2 + 8e ⇒ 4O 2 3 2 Ru T  PH 2 PCO PO2  N=E + ln 3 2 8F  PH 2O PCO2 Ptot  o − H2 and CO Electrochemistry     • Electrical field submodel to calculate electrical potential field in all conducting regions including electrodes, current collectors, interconnects ∇⋅ = ρ − Ohmic heat generation i = −σ∇φ − Current Flow i Cat ho de i Electr olyte Ano de Vn Rn In • Parallel Code for PC cluster computing Vn = Nernst Pot ential - Ov er potent ials Rn = Loc al Lumped Resist ance (ohmic + electroc hemical losses) • Model temperature output coupled to ANSYS FEA code for stress analysis U.S. Department of Energy Pacific Northwest National Laboratory SECA Worksho p (war ) / M arch 2 1, 20 02 12 Example: Simple Co-Flow Channel Displacement Anode Current C ol lector Fuel Out Oxi di zer Out E tr lec te ol y Anode Cathode Fuel In Cat hode Current C ol lector Ox idizer In Str esses Current Density on Electrolyte-Cathode Face (Amp/m2) SECA Worksho p (war ) / M arch 2 1, 20 02 Planned Capabilities and Validation • Extend to Stacks • Internal Reforming • Include Contact Resistance − Current collector-electrode − Electrode-electrolyte − Current collector-interconnect • Complete Model Validation − Data from open literature − Data from NETL testing facilities − Data from SECA partners • Working with SECA partners in Model Validation and Application − Delphi − Siemens -Westinghouse Siemens-Westinghouse SECA Workshop (war) / March 21, 2002 Solid Oxide Fuel Cell Materials Research at Argonne National Laboratory U.S. Department of Energy Pacific Northwest National Laboratory 15 Drivers for the research • A major approach to lowering fuel cell and balance-ofplant costs is to reduce SOFC operating temperatures to <800oC. At the lower temperatures, however, – Conventional LSM cathode performance is inadequate • Need to develop perovskite and other cathode materials with high electrochemical activity, low resistivity at <800o C – Sulfur-poisoning of Ni anode is exacerbated • Need anode materials tolerant to 1-100 ppm or more of H2S – Metallic interconnect (bipolar) plates become feasible • Need new alloys or coatings as presently available metals and alloys degrade rapidly in SOFC environments Argonne Elec trochemical Technology Program U.S. Department of Energy Pacific Northwest National Laboratory 16 Low-Temperature Cathode Materials Single-phase cathode materials • Accomplishments – Identified Sr-doped lanthanum ferrates as the most promising candidate cathode materials – Verified stable performance to 500 h 3 Areal Resistance/Ω.cm2 15 Area Specific Resistance/ Ω.cm2 LSF (LS)0.8F LSFC 10 5 0 750 800 850 Temperature/°C 650 700 SrCeC SrCeF PrSC Cathode LSF Composition 2 1 0 0 100 200 300 400 Time/Hou rs 500 Argonne Elec trochemical Technology Program U.S. Department of Energy Pacific Northwest National Laboratory 17 Metallic Interconnect Materials Approach • Alloys similar to ferritic stainless steels – reduce Cr, other elements that can degrade fuel cell performance – additives to improve properties and protective scale • Materials of graded composition to impart optimum chemical stability at each surface • Novel processing technique can yield almost any desired shape – flat, corrugated, textured, functionally graded – can incorporate flow fields, internal manifolds Formed Flow Field in Dense Material Formed Flow Field with Porous Layers Macroporous Flow Field Argonne Elec trochemical Technology Program U.S. Department of Energy Pacific Northwest National Laboratory 18 Metallic Interconnect Materials Multi-layer plates are easily formed • Compositionally graded specimens can be fabricated • Samples show excellent bonding • After 400 h at 800oC, there was no observed elemental diffusion between layers • 10-Layer specimen Two surface layers: Fe-Cr-La-Y-Sr alloy Bulk: SS Type 434 • Points 1,2: ~1.5 - 2.0 wt% La • Points 3,4: no measurable La SE M Micro graph of compositionally-graded sample Argonne Elec trochemical Technology Program U.S. Department of Energy Pacific Northwest National Laboratory 19 Summary Future directions • Micro-engineer the cathode-electrolyte interface to further improve cathode performance • Evaluate anode materials with 0-100 ppm H2S in fuel gas • Characterize oxide scale on metallic bipolar plates for growth rates and electrical conductivity • Test developed materials in full cell and short stack configurations Argonne Elec trochemical Technology Program U.S. Department of Energy Pacific Northwest National Laboratory 20 Effect of Oxidant Composition on a High Performance, Anode-Supported Cell 1.2 3.0 800 C 1.0 100% O2 + 0% N2 21% O2 + 79% N2 o 2.5 Slope = 0.084 Ω .cm Rohm = 0.088 Ω .cm 2 2 MPD ~2.9 W/cm2 With H2 /O 2 Power Density (W/cm ) Voltage (V) 0.8 0.6 0.4 2.0 1.5 1.0 MPD ~1.75 W/cm2 With H2 /Air Slope = 0.140 Ω .cm 2 2 0.2 0.0 Rohm = 0.104 Ω .cm 2 0.5 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Current Density (A/cm ) 2 Funding: DOE/NETL Good Cathode: But Needs to be Better U.S. Department of Energy Pacific Northwest National Laboratory 21 O 2-N 2 Effective Diffusivity through Porous LSM and Cathodic Concentration Polarization Experimentally Measured Effective Diffusivities 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 0.10 Low Diffusivity Calculated Cathodic Concentration Polarization High Polarization 0.022 0.020 0.018 O2-N 2 Effective Diffusivity through 2 Porous LSM(cm /s) High Diffusivity Cathode Overpotential (V) Porosit y created b y adding carbon, and burning it off. 0.016 0.014 0.012 0.010 0.008 0.006 0.004 0.002 0.000 0 .0 20 w C t% 22.5 w C t% 25 w C t% 27.5 w C t% 30 w C t% Thickness = 50 µm Low Diffusivity 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 2 1 .6 1 .8 2 .0 2 .2 O Porosity pen C urrent Density (A/cm ) High Diffusivity Low Polarization Funding: DOE/NETL Cathode Concentration Polarization is Smallof Energy U.S. Department Pacific Northwest National Laboratory When Porosity is High 22 SOFC Cell Performance at Reduced Temperatures 1.4 1.4 80 0C 1.2 75 0C 1.2 1 70 0C 65 0C 1 P ow er D ens ity , W / cm 2 C e ll V o lta ge , V 0.8 0.8 0.6 0.6 0.4 0.4 60 0C 0.2 Hydrogen fuel Air oxidant 0.2 0 0 0.5 1 1.5 C urr ent De ns it y, A/ cm 2 0 2 2.5 3 ••High power densities (e.g., 0.9 W/cm² at 650°C) achieved at reduced High power densities (e.g., 0.9 W/cm² at 650°C) achieved at reduced temperatures (<800°C) with anode-supported thin-electrolyte cells temperatures (<800°C) with anode-supported thin-electrolyte cells U.S. Department of Energy Pacific Northwest National Laboratory 23 Pressurized Operation of Planar SOFCs Expe rimen tal Data Points and Mo de l 1.2 1.1 Cell Vo ltage (V), Fuel Utilization 1 0.9 0.8 PD, W/cm 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 2 2 0.4 0.3 0.2 1 Fu el u ti li za ti on 2 3 a tm 0.1 0 0.5 0.6 0.7 Cu rrent De nsity, A/cm ••First pressurized SOFC with planar anode-supported thin-electrolyte cells First pressurized SOFC with planar anode-supported thin-electrolyte cells U.S. Department of Energy Pacific Northwest National Laboratory 24 YSZ film deposited from polymeric precursor on sapphire substrate A) Annealed at 400°C for 4 hours B) Annealed at 1000°C for 4 hours U.S. Department of Energy Pacific Northwest National Laboratory 25 Cross section - 1 Y S Z P orou s C eO 2 Cross section - 2 Y S Z P oro u s C eO 2 P orou s L S M U.S. Department of Energy Pacific Northwest National Laboratory 26 LBNL Developed Colloidal Deposition Technique for SOFCs LBNL Developed Colloidal Deposition Technique for SOFCs NiO/YS Z substrate (presse d) NiO/YS Z fire d at 950 oC NiO/YS Z substra te with green YSZ film NiO/YS Z-YSZ bilayer fired at 1400 oC Dip-coat, aerosol spray, EPD... •Geometry Independent •Low Cost •Scaleable U.S. Department of Energy 3 Pacific Northwest National Laboratory 27 Development of Alloy Supported Thin-film SOFC Structures to Reduce Stack Cost and Improve Reliability Pt Top view of a YSZ/NiYSZ/FeCr alloy SOFC bilayer (looking through transparent YSZ film). Bottom view of a YSZ/Ni-YSZ/FeCr alloy SOFC bilayer (at porous FeCr electrode) Metallic Support U.S. Department of Energy 5 Pacific Northwest National Laboratory 28 Anode YSZ Objectives and Tasks Objectives: S Develop technology leading to reforming of diesel fuel for APU applications. S Understand parameters that affect fuel processor lifetime and durability. S Examine fuel components, impurities and additives S Quantify fuel effects on fuel processor performance S Understand the parameters that affect fuel processor lifetime and durability S Catalyst durability S Carbon formation and catalyst durability STasks: S Carbon Formation Measurement of Diesel Fuel(s) S Equilibrium and component modeling S Experimental carbon formation measurement S Fuel Mixing S Vaporization / Fuel atomization S Direct liquid injection S ‘Waterless’ Partial Oxidation of Diesel Fuel S Start-up S SOFC anode recycle Fuel Cell Program U.S. Department of Energy Pacific Northwest National Laboratory 29 Partial Oxidation Stage Outlet Concentrations (for similar oxygen conversion) Higher Temperatures (O/C ratio’s) are required for long chained hydrocarbon conversion for similar residence times – leads to H2 dilution Longer residence times required for similar conversion (same Temperature / O/C) residence time (iso-octane ~ 10 msec) residence time (dodecane ~ 45 msec) 40 35 H 2+C O Unconv erted O2 % Outlet Concentration 30 25 20 15 10 5 0 Iso-Octane Fuel Cell Program Iso-Octane plus 20 % Xylene Dodecane U.S. Department of Energy Pacific Northwest National Laboratory 30 Diesel POx/Reforming Light-off Reactor start-up with kerosene / no water water availability during initial operation 1000 Reformer Outlet Temperatur e / C 900 800 700 600 500 400 300 200 100 0 3800 3820 3840 3860 3880 3900 3920 3940 3960 3980 4000 o Reformer Lightoff Time / sec Fuel Cell Program U.S. Department of Energy Pacific Northwest National Laboratory 31 Fuel / Water co-vaporization Issues Co-vaporization of water and fuel in external vaporizer uses water as carbon formation suppressant / fuel carrier Co-vaporization produces periodic ‘distillation’ and reactor temperature exotherms 100 0 95 0 90 0 85 0 80 0 75 0 30 0 70 0 65 0 60 0 1 500 0 1 510 0 1 520 0 1 530 0 1 540 0 1 550 0 1 560 0 1 570 0 1 580 0 25 0 32 5 Re for me r Te mpe ra ture deg C R ea ctor F u el In let Te mpe ra ture deg C 37 5 40 0 R eform er Ou tl et Tem pera tu re /C o 35 0 Vaporizer outlet temperature 27 5 Fuel Cell Program Time / sec of Energy Pacific Northwest National Laboratory 32 1U.S. Department 590 0 1 600 0 Fuel Inl et Tem pera tu re / C Reactor outlet temperature o Technical Summary/Findings • Catalytic oxidation / reforming • Diesel Fuel Components (Dodecane) • Long chained hydrocarbons require higher residence time for conversion • aromatics slow and inhibit overall reaction rate • Pre-combustion • Diesel fuels much more likely for pre-combustion • Kerosene has higher pre-combustion tendencies than de-odorized kerosene • Carbon Formation • Hysteresis observed after on-set of carbon formation • Greater carbon formation with aromatics Fuel Cell Program U.S. Department of Energy Pacific Northwest National Laboratory 33 Technical Results: Carbon formation measurements Carbon formation monitoring with laser scattering Odorless Kerosene; S/C = 1.0 40 35 30 R e la t iv e Abs o r b Results • Partial oxidation of • odorless kerosene • kerosene • dodecane • hexadecane • Carbon formation monitoring by laser optics • Carbon formation shown at low relative O/C ratios and temperature with kerosene (left) • Demonstrated start-up with no water – carbon formation observed after ~ 100 hrs ofU.S. Department of Energy operation Pacific Northwest National Laboratory 34 25 20 15 10 5 0 0. 2 0. 4 0. 6 O / C R a ti o 0. 8 1 40 35 30 La ser Abso rp tio n (% ) 25 20 15 10 5 0 6 70 6 80 6 90 7 00 7 10 7 20 7 30 A iab atic R acto r Outl et T em peratu re (oC) d e Fuel Cell Program NETL Fuel Processing Team Fuel Desulfurization - “SCOHS” • • • Challenge: Limited sulfur tolerance in fuel cell reformer & stack NETL Research: Selective Catalytic Oxidation of H2S Benefit: Fuel cells using coal gas, nat. gas, transportation fuels H 2 S + 1/2 (O2 + 3.76 N2) = 1/n Sn + H 2O + 1.88 N2 1” NETL SCOHS Catalyst Sulfur product continuously drips out. U.S. Department of Energy Pacific Northwest National Laboratory E/MM0680P GAR 3/00 35 NETL Fuel Processing Team Fuel Desulfurization - “SCOHS” • • Removal Efficiency: SCOHS has part per trillion (ppt) thermodynamic sulfur removal efficiencies. Water Sensitivity: Unlike most metal oxide based systems, SCOHS is relatively insensitive to water content, which can be found in high concentrations in some reformate streams. SCOHS - Thermodynamic Removal Eff. Equilibrium H2 S Concentration (ppmv) Zinc Titanate - Thermodynamic Removal Eff. 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 1.00E-01 1.00E-02 1.00E-03 1.00E-04 1.00E-05 1.00E-06 1.00E-07 0 H2 O Content 0.025 _ H2S Conc. (ppbv) 0.02 H2O/H2S = 0.0 0.015 0.01 0.005 0 0 0.1 ppmv SOFC H2O/H2S = 1.0 H2O/H2S = 10 H2O/H2S = 100 200 0.5% 400 600 800 o Temperature ( C) 1% 2% 5% 10% 1000 20% 1200 40% 0.1% 100 200 300 400 Temperature (°C) U.S. Department of Energy Pacific Northwest National Laboratory E/MM0680P GAR 3/00 36 NETL Fuel Processing Team NETL Fuel Processing Team Fuel Processor “APU” Fuel Processor - -“APU” Air Compressor Air Preheater 800 C SECA APU 800 °C Combustor 650 °C Fuel Cell Stack 800 °C Cathode Fuel Pump AutoThermal Reformer 800 °C 800 °C Water Pump Steam Generator Anode 800 °C Desulfurizer Sorbent Bed ATR Oxygen-to-Carbon Ratio - 0.25 ATR Steam-to-Carbon Ratio - 0.7 Fuel Cell / Reformer Temperature - 800 C Exhaust Condenser Desulfurizer Temperature Efficiency Net Power Output Mass Specific Fuel Consumption 1” 150/400 C 52.82 5 kW .75E-3 kgmol / kW hr 800 C 55.09 5 kW .722E-3 kgmol / kW hr U.S. Department of Energy Pacific Northwest National Laboratory E/MM0 680P GAR 3/00 37 Additional SECA Core Program Participants Technology Mana gem ent, Inc. Benson Le e University of Florida Eric Wac hsm an Northwes tern University/ Applied Thin Films Scott Barnett Georgia Institute of Technology/ Meilin Liu NexTech Mate rials, Ltd. Bill Daws on Ceramate c S. E langovan Oak Ridge Na tional Lab Edgar Laura- Curzio Don Adam s Don Adams Demonstrate the opera tion of two SO FC modules as a s ingle unit. Develop Screen Printing Manufacturing Technique Develop Bi-Layer Ceria, Bismuth O xide ele ctrolyte for low tem pe rat ure operation. Develop ionic conduction mode l. Develop segmented in s eries SO FC des ign. Develop internally reforming anode as disc uss ed in “Na ture” Developm ent of ultra-low (500 C) temperature SO FC materials. Developm ent of in-situ FTIR em is sion spec troscopy f or eva luation of gas-solid interactions in fue l cells. Developm ent of c athode supporte d SOFC designs . Developm ent of m anufa cturing techniques for low temperature SO FC materials Inte rconne cts Developm ent of Low Tem perature m ateria l set. SO FC material property a nd reliability eva luations Power Electronics evaluat ion. U.S. Department of Energy Pacific Northwest National Laboratory Descr i tor -- include initials, /o rg#/ date Descriptor include initials, /org#/date p 38