Integrated Micropower Generator

Sossina Haile, David Goodwin, CaltechSteve Visco, Lutgard de Jonghe, Craig Jacobson, LBNL

Scott Barnett, Northwestern UniversityPaul Ronney, University of Southern California

Micro-SOFC

Swiss RollCombustor

+

High EfficiencyThermal Management

Integrated MicroPower Generator Review, 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)

– 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

Integrated MicroPower Generator Review, 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 Generator Review, Oct. 18, 2002

Concept

Components

• “Swiss roll” heat exchanger– Heat incoming gas with

(cooling) outgoing gases

• Reduced temperature SOFC (300-500ºC)– 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

Products out

A ir inAir/fuel in

- out+ out

Products

air/fuel reactants

catalyticcombustor

SCFCstack

• Targets– Power density: 50-100mW/cm2, – Total volume: ~2 × 2 × 1.5cm3

– Total weight: ~10g

Integrated MicroPower Generator Review, Oct. 18, 2002

Swiss Roll Thermal Management

Strategy: Transfer heat from exhaust to incoming gases

Combustion volume

Products

Reactants

1500K 1200K 500K 400K 300K

1500K 1500K 800K 700K 600K• 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 500C can be maintained

Integrated MicroPower Generator Review, Oct. 18, 2002

Single Chamber Solid Oxide Fuel Cells

CH4 + ½ O2 CO + 2H2

H2 + O= H2O + 2e-

CO + O= CO2 + 2e-

C nH 2 n+ 2 O 2O 2

O =

C

C

O

O

+

+

C O 2 + H 2

H 2

O

c athodea node

e -e -

½ O2 + 2e- O=

strip

stackedconventional SOFC

fuel oxidant

CH4 + 4O=

CO2 + 2H2O +8e-½ O2 + 2e- O=

fuel + oxidant by-products

• Hibino et al. Science (2000)• Fuel & oxidant mixed• Best reported performance

– Power density: 644 mW/cm2

– Conditions: CH4 + Air; 550C

• Strip or stacked geometry

seals

Integrated MicroPower Generator Review, Oct. 18, 2002

State of the Art in SCFCs

• Multilayer geometry (1-cell)

• Ce0.8Sm0.2O1.9 (150m)

• 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

Hibino et al. Science (2000)

Hibino et al. J. Electrochem. Soc. (2000)

550°C0.5mm

0.15mm

550°Cethane

Limited by electrolyte resistance!

Integrated MicroPower Generator Review, 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 Generator Review, 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 Generator Review, Oct. 18, 2002

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

Integrated MicroPower Generator Review, 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 Generator Review, 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 Generator Review, 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 Generator Review, 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 celldevelopment

Design optimizationvia simulations

Catalystdevelopment

Fuel cellfabrication

Systemintegration