Integrated Micropower Generator Sossina Haile, David Goodwin, Caltech Steve Visco, Lutgard de Jonghe, Craig Jacobson, LBNL Scott Barnett, Northwestern University Paul Ronney, University of Southern California Micro- SOFC Swiss Roll Combustor + High Efficiency Thermal Management

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Outline Program Overview (Haile) –Power Generation Strategies –Integrated Micropower Generator (IMG) –Swiss Roll Heat Exchanger –Single Chamber Fuel Cell (SCFC) Technical Program –SCFC Modeling (Goodwin) –SFCF Development (Barnett, Haile) –Fuel Cell Fabrication (Visco) –Afterburner Catalysts (Haile) –Swiss Roll Heat Exchanger: Simulation & Fabrication (Ronney) Administrative Aspects (Haile) –Research Schedule and Milestones –Management & Reporting

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Micropower Generation Strategies High power density vs. High energy density Thermoelectrics (thermal to electric) –Manufacture by electrodeposition and MEMS methods –Heat source required, low efficiency (5%) Microturbines (chemical to mechanical to electric) –Reasonable efficiency, fuel flexibility –High RPM  tight tolerances, friction losses Lithium batteries (“chemical” to electric) –Low maintenance, simple system –Insufficient energy density Fuel Cells (chemical to electric) –Chemical fuels have high energy and power densities –Heat loss has limited micro-FCs to low temperatures –Lower efficiency, poor fuel flexibility

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Integrated Micropower Generator Components “Swiss roll” heat exchanger –Heat incoming gas with (cooling) outgoing gases Reduced temperature SOFC ( ºC) –Minimize thermal stress –Maintain high T advantages Single chamber fuel cell –Insensitive to cracks Catalytic after-burner –Maintain temperature –Consume unreacted hydrocarbons Micro-aspirator

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Swiss Roll Thermal Management Strategy: Transfer heat from exiting gases to those incoming Linear counterflow heat exchanger Linear device rolled up into 2-D “Swiss Roll” 2-D device rolled up into toroidal “Swiss Roll”

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Background: Single Chamber Fuel Cells CH 4 + ½ O 2  CO + 2H 2 H 2 + O =  H 2 O + 2e - CO + O =  CO 2 + 2e - Hibino and co-workers First demonstration: 1993 Ba(Ce 0.8 Y 0.2 O 3 ) electrolyte Pd anode, Ag cathode, 950°C Strip or multilayer geometry ½ O 2 + 2e -  O = minimize IR? strip multilayer conventional SOFC fueloxidant

Integrated MicroPower GeneratorReview, Oct. 18, 2002 State of the Art in SCFCs Multilayer geometry (1-cell) Ce 0.8 Sm 0.2 O 1.9 (150m) Ni-SDC (10:90 wt) Sm 0.5 Sr 0.5 CoO 3 Variety of fuels, 18 vol% in air 1 – 10 cm/sec fluid velocities Ethane  highest power –400 mW/cm 2, 500°C Hibino et al. Science (2000) Hibino et al. J. Electrochem. Soc. (2000) 550°C 0.5mm 0.15mm 550°C ethane Limited by electrolyte resistance!

Integrated MicroPower GeneratorReview, Oct. 18, 2002 SCFC Operational Parameters Component materials: Electrolyte and Electrodes –Initial demonstrations, mixed O = / H + conducting electrolyte –Recent experiments, O = conductor –Reactions appear simpler with O = conductor –Need for ‘reduced temperature’ components/materials Multi-cell Geometry –Multilayer stack allows greater design flexibility than strip –Extensive experience in multilayer stacks at LBNL –Experiments begin with anode or electolyte supported design Fuels –Methane, ethane, propane, butane all demonstrated –Propane offers best microaspiration characteristics, handle as a liquid, relatively easy partial oxidation –Simulations begin with methane and propane

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Early Design Decisions Electrolyte, anode, cathode and fuel selection highly interdependent Initial Proposal: parallel investigations –H + and O = conducting electrolytes –Methane, ethane, propane and higher hydrocarbons DARPA Feedback: early selection –O = conducting electrolye –Propane fuel Program restructuring –Eliminate H + based SCFC development (CIT) –Redistribute O = based SCFC development effort

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Operational Targets Fuel cell performance: 50 – 100 mW/cm 2 Total fuel cell area: 2.5cm 2 Device power output: 125 – 250 mW 5 cell stack vol: (1  0.5 cm 2  0.2 cm  5) 1 cm/edge for 2-D Swiss roll Device total: 2  2  1.5 cm 3, ~ 10g Propane, 2 cm 3 tank, 40% efficiency  0.8Wh/cm 3, 0.6 Wh/g

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Challenges and Opportunities Catalysts –Highly selective cathode and anode –Afterburner –Reaction pathways Design & operation parameters –Fuel-to-air ratio, bypass air ratio –Flow rates, residence times –Fuel cell channel thickness, area –Swiss roll channel thickness, # turns Computational effort –Avoid costly Edisonian “try and tinker” approach

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Challenges and Opportunities Fabrication: fuel cell and heat exchanger –Fuel cell materials compatibility –Multilayer fuel cell vs. single layer with strip electrodes –Anode vs. cathode supported design –Thermally insulating oxides for Swiss roll structure –Incorporation of fuel cell into Swiss roll heat exchanger –Supplementary air intake for complete combustion –Power extraction via appropriate wiring –Start-up via self-starting fuels/catalysts or battery powered resistive heating

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Revised Responsibilities Electrolyte selection Fuel selection SCFC simulation & model experiments Cathode materials Anode materials SCFC fabrication Swiss roll modeling & fabrication Catalytic afterburner Microaspirator Complete (doped ceria) Complete (propane) D. Goodwin & S. Haile (CIT) S. Haile (CIT) + NWU S. Barnett (NWU) + CIT S. Visco (LBNL) P. Ronney (USC) S. Haile (CIT) + USC P. Ronney (USC)

Integrated MicroPower GeneratorReview, Oct. 18, 2002 Integrated Effort Cathode Dev. Catalyst Dev. S. Haile, Caltech Anode Dev. S. Barnett, NWU Swiss Roll Fab. System Simulations P. Ronney, USC Fuel Cell Fab. Integration w/Swiss Roll LBNL team Fuel Cell Simulations D. Goodwin, Caltech Fuel cell development Design optimization via simulations Catalyst development Fuel cell fabrication System integration