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

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

3. 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
High power => a lot of sudden umph
High energy => use at lower power for a long time

4. Concept Components “Swiss roll” heat exchanger
Heat incoming gas with (cooling) outgoing gases
Reduced temperature SOFC ( ºC)
Minimize thermal stress
Retain high T advantages
Single chamber fuel cell
No seals required
Insensitive to cracks
Catalytic after-burner
Maintain temperature
Consume unreacted hydrocarbons
Micro-aspirator
Targets
Power density: mW/cm2,
Total volume: ~2 × 2 × 1.5cm3
Total weight: ~10g

5. Swiss Roll Thermal Management
Strategy: Transfer heat from exhaust to incoming gases
Linear counterflow heat exchanger
Linear device rolled up into 2-D “Swiss Roll”
2-D device rolled up into toroidal “Swiss Roll”
Temperatures significantly greater than 500C can be maintained

6. Single Chamber Solid Oxide Fuel Cells
Hibino et al. Science (2000)
Fuel & oxidant mixed
Best reported performance
Power density: 644 mW/cm2
Conditions: CH4 + Air; 550C
Strip or stacked geometry
CH4 + ½ O2  CO + 2H2
H2 + O=  H2O + 2e-
CO + O=  CO2 + 2e-
fuel + oxidant
by-products
½ O2 + 2e-  O=
conventional SOFC
stacked
fuel
oxidant
strip
CH4 + 4O=
 CO2 + 2H2O +8e-
½ O2 + 2e-  O=
seals

7. State of the Art in SCFCs
Hibino et al. Science (2000)
Multilayer geometry (1-cell)
Ce0.8Sm0.2O1.9 (150mm)
Ni-SDC (10:90 wt)
Sm0.5Sr0.5CoO3
Variety of fuels, 18 vol% in air
1 – 10 cm/sec fluid velocities
Ethane  highest power
400 mW/cm2, 500°C
550°C
ethane
Limited by electrolyte resistance!
550°C
0.5mm
0.15mm
Hibino et al. J. Electrochem. Soc. (2000)

8. 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

9. 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

10. Operational Targets Fuel cell performance: 50 – 100 mW/cm2
Total fuel cell area: 2.5cm2
Device power output: 125 – 250 mW
5 cell stack vol: (1  0.5 cm2  0.2 cm  5)
1 cm/edge for 2-D Swiss roll
Device total: 2  2  1.5 cm3, ~ 10g
Propane, 2 cm3 tank, 40% efficiency  0.8Wh/cm3, 0.6 Wh/g

11. 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
Butane: 13.6 Wh/g, 7.7 Wh/ml

12. 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

13. 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

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