Fuel Cells for a Sustainable Energy Future Sossina M. Haile Materials Science / Chemical Engineering California Institute of Technology

Contents

• The Problem of Energy – Growing consumption – Consequences – Sustainable energy resources

• Fuel Cell Technology Overview – Principle of operation – Types of fuel cells and their characteristics

• Recent (Caltech) Advances – Too many to cover…

Towards a Sustainable Energy Future

The Problem of Energy • The Problem – Diminishing supply? – Resources in unfriendly locations? – Environmental damage?

• The Solution – Adequate domestic supply – Environmentally benign – Conveniently transported – Conveniently used

Towards a Sustainable Energy Future

200 150

260

Coal

208

Natural Gas

156

100

104

Total Renewables 50

52

Hydroelectric Other Renewables

0 1980

1990

2000

2010

8

12

Oil

Projections

18

History

Exa Joules (10 )

Energy, Quadrillion BTU

250

6

4

2

Nuclear 0

2020

Equivalent Power (TW, 10 )

World Energy Consumption

0

2030

Year 2005 totals: 2030 projections:

490 Q-Btu, 515 EJ, 720 Q-Btu, 760 EJ,

Towards a Sustainable Energy Future

16TW 24TW

86% fossil 81%

Source: US Energy Information Administration

Fossil Fuel Supplies Source: US Energy Information Administration

2.0E+05

(Exa)J

1.5E+05

Rsv = Reserves (90%) Rsc = Resources (50%)

1.0E+05

Unconv Conv

5.0E+04 0.0E+00 Oil Rsv

Oil Rsc

Gas Rsv

Gas Rsc

Coal Rsv

Coal Rsc

Source

Reserves, yrs

Resources, yrs

Total, yrs

Oil

13 - 20

10 – 35

23 - 55

Gas

11 - 25

7 – 40

18 - 65

Coal

32

270

300

56-77

287-345

Towards a Sustainable Energy Future

> 400 yrs

Reserves History for American Coal Courtesy: David Rutledge

Reserves, Gt

1,500

Coal Commission (based on surveys by Marius Campbell of the USGS) 4,045 years

1,000 Paul Averitt (USGS) 2,136 years 1,433 years

500

0 1920

Bureau of Mines/EIA (based on Paul Averitt’s surveys) 368 years 270 years 236 years

1960

2000

“Hubbert Peak” type of analysis suggests 90% depletion by 2076 Towards a Sustainable Energy Future

US Energy Imports/Exports: 1949-2004 Source: US Energy Information Administration

Imports

6

25

Total

20 15 10 5 0 1950 1960 1970

Quad BTU

35

Exports Total

5 Quad BTU

Quad BTU

35 30

Net

30 25 20 15 10 5

Petroleum 1980

1990

2000

4 Coal

3 2

Petroleum

1 0 1950

1960

1970

1980

1990

2000

• 65% of known petroleum reserves in Middle East • 3% of reserves in USA, but 25% of world consumption

1957: Net Importer

0 1950

1960

1970

Towards a Sustainable Energy Future

1980

1990

2000

Environmental Outlook Global CO2 levels

atmospheric CO2 [ppm]

340

2006: 382 ppm 330 320 310

Projections: 500-700 ppm by 2020

• Anthropogenic

300 290

Industrial Revolution

– Fossil fuel (75%) – Land use (25%)

280 270

1000

1200

1400

Source: Oak Ridge National Laboratory Towards a Sustainable Energy Future

1600

year

1800

2000

Environmental Outlook CO2 in 2006: 382ppmv

300 275 250

-- CO2 -- CH4 -- ΔT

700

+4 0

600 500

-4

200

400

-8

175

300

225

400

300

200

100

ΔT relative to present (°C)

CO2 CH4 (ppmv) (ppmv) 800 325

0

Thousands of years before present (Ky BP) Intergovernmental Panel on Climate Change, 2001; http://www.ipcc.ch N. Oreskes, Science 306, 1686, 2004; D. A. Stainforth et al, Nature 433, 403, 2005 Towards a Sustainable Energy Future

Observations of Climate Change

• • • • • • • •

Evaporation & rainfall are increasing More of the rainfall is occurring in downpours Corals are bleaching Glaciers are retreating Sea ice is shrinking Sea level is rising Wildfires are increasing Storm & flood damages are much larger

Towards a Sustainable Energy Future

Greenland Ice Sheet Melt Extent

Towards a Sustainable Energy Future

More Observations of Global Climate Change 1910

Grinnell Glacier and Grinnell Lake Glacier National Park

Coral Bleaching 1977

Towards a Sustainable Energy Future

Future Scenarios Courtesy: John Seinfeld

Most optimitistic scenario

Towards a Sustainable Energy Future

Centuries for CO2 to decay

Future Scenarios Highly optimitistic scenario: stabilize at 380 ppm

(aerosols)

Towards a Sustainable Energy Future

Energy Outlook Supply • Uncertainty in assessing • High geopolitical risk • Rising costs

Environmental Impact • Target – Stabilize CO2 at 550 ppm – By 2050

• Requires – 20 TW carbon-free power – One 1-GW power plant daily from now until then

Urgency • Transport of CO2 or heat into deep oceans: – 400-1000 years; CO2 build-up is cummulative

• Must make dramatic changes within next few years

Towards a Sustainable Energy Future

The Energy Solution 1.2 x

105

Solar

The need: ~ 20 TW by 2050

TW at Earth surface 600 TW practical

Wind

Biomass

2-4 TW extractable

5-7 TW gross all cultivatable land not used for food

Tide/Ocean Currents 2 TW gross

Geothermal 12 TW gross over land small fraction recoverable

Nuclear

Waste disposal 60 yr uranium supply Towards a Sustainable Energy Future

Hydroelectric 4.6 1.6 0.9 0.6

TW TW TW TW

gross technically feasible economically feasible installed capacity

Fossil with sequestration

1% / yr leakage -> lost in 100 yrs

The Energy Solution • Sufficient Domestic Supply – Coal, Solar, Nuclear (near term)

• Environmentally Sustainable Supply – Solar, Coal with sequestration?

• Suitable Carrier – Electricity? Hydrogen? Hydrocarbon?

• Challenges – Convert solar to convenient chemical form – Efficient utilization of chemical fuel – Cost-effective technologies

Towards a Sustainable Energy Future

Caltech Center for Sustainable Energy Research Conversion ity c i r ct Ele H2O, CO2

H2O, CO2

Utilization

Photovoltaic and photolysis power plants

Fuel cell power plant

Electric power, heating

Towards a Sustainable Energy Future

Fuel: H2 or CH3OH

Storage

Harry Atwater Harry Gray Sossina Haile Nathan Lewis

Fuel Cells: Part of the Solution? • High efficiency automotive engine: 50-75 kW

80

– low CO2 emissions

efficiency [%]

• Size independent 60

Fuel Cells

40

Co

20

• Various applications

*

– stationary

ne i g n E on i t s u b m

s

– automotive – portable electronics

• Controlled reactions 0 0

5

10

15

20

power plant size [MW]

25

– “Zero Emissions”

• Operable on hydrogen – (if suitably produced)

*Can be as high as 80-90% with co-generation Towards a Sustainable Energy Future

Fuel Cell: Principle of Operation best of batteries, combustion engines

conversion device, not energy source

Anode

Cathode

eH+

H2 H2 → 2H+ + 2e-

O2 ½ O2 + 2H+ + 2e- → H2O

Electrolyte Overall: H2 + ½ O2 → H2O Towards a Sustainable Energy Future

Fuel Cell Performance

1.2

1.17 Volts (@ no current)

cross-over 1.0

– reaction kinetics – electrolyte resistance – slow mass diffusion

• power = I*V • peak efficiency at low I • peak power at mid I

Towards a Sustainable Energy Future

Voltage [V]

• voltage losses – fuel cross-over

0.8 theoretical voltage

slow reaction kinetics

0.8

0.6

peak power

0.6

0.4

0.4

electrolyte resistance

0.2 0.0 0.0

0.2 slow mass diffusion

0.4

0.8

1.2

Current [A / cm2 ]

0.0 1.6

Power [W / cm2]

H2 + ½ O2 → H2O

Fuel Cell Types Types differentiated by electrolyte, temperature of operation Portable Type °C Fuel Electrolyte

Ion Oxidant

PEM 90-110

AFC 100-250

H2 + H2O

H2

Nafion H3O+ ↓

KOH OH- ↑

O2

Stationary PAFC 150-220

⌧ H2

MCFC

SOFC

500-700

700-1000

HC + CO

HC + CO

H3PO4 Na2CO3 H+ ↓ CO32- ↑ Corrosive liquids O2 O2 + H2O O2 + CO2

Fuel flexibility, efficiency

O2

Easy thermal cycling

Target regime Towards a Sustainable Energy Future

Y-ZrO2 O2- ↑

New Electrolytes: Solid Acids • Chemical intermediates between normal salts and normal acids: “acid salts” • Physically similar to salts • Structural disorder at ‘warm’ temperatures • Properties Direct H+ transport Humidity insensitive Impermeable 2 Water soluble!! Brittle Towards a Sustainable Energy Future

log(conductivity)

½(Cs2SO4) + ½(H2SO4) → CsHSO4

disordered structure

polymer

normal structure structural transition T

.

1/T

Proton Transport Mechanism

H S O

Sulfate group reorientation 10-11 seconds

Proton transfer 10-9 seconds

Towards a Sustainable Energy Future

Fuel Cell Operation Fine CsH2PO4

100 sccm 200 sccm

2 μm

Slurry deposit

Voltage ( V )

T = 248°C 1.0 8 mg Pt/cm2

0.5 0.4

0.8 0.3 0.6 0.2 0.4 0.1

0.2

36 μm electrolyte

0.0 0.0

0.5

1.0

0.0 2.0

1.5 2

Current density ( A / cm ) 10-40 μm pores, ~40% porosity Open circuit voltage: 0.9-1.0 V Towards a Sustainable Energy Future

T. Uda & S.M. Haile, Electrochem & Solid State Lett. 8 (2005) A245-A246

Peak power density: 285-415 mW/cm2

2

1.2

Power density ( W /cm )

H2, H2O | cell | O2, H2O

Impact S. M. Haile, D. A. Boysen, C. R. I. Chisholm and R. B. Merle, “Solid Acids as Fuel Cell Electrolytes,” Nature 410, 910-913 (2001).

The promise of protonics

Solid Acids Show Promise... Some Like It Medium Hot

Nature: News & Views

Physics Today Online Science Now Magazine

Towards a Sustainable Energy Future

From Breakthrough to Product Calum

2001

2007 1 mg Pt for 200 mW

Dane

2.5 g Pt for 60 W bulb ~ $100 in Pt

1 cm2 of fuel cell area 36 mg Pt for 10 mW 43 g Pt for 60 W bulb ~ $9,000 in Pt

Towards a Sustainable Energy Future

Tom Friedman talking to his wife on an SAFC powered cell phone MVI_1924.avi

New Cathodes for Solid Oxide Fuel Cells • Traditional cathodes

(Ba0.5Sr0.5)(Co0.8Fe0.2)O2.3

– A3+B3+O3 perovskites – Poor O2- transport – Limited reaction sites almost 1 in 4 vacant

• Our approach – High O2- flux materials – Extended reaction sites – A2+B4+O3 perovskites electrode bulk path

‘triple-point’ path O2

O2 Oad O2-

Oad 2e-

cathode

electrolyte

Towards a Sustainable Energy Future

Oad

O2-

2ecathode O2-

electrolyte

Cell Fabrication Dual dry press NiO + SDC (Ce0.85Sm0.15O2)

SDC

Sinter, 1350oC 5h

NiO + SDC Spray cathode

Calcine, 950oC 5h, inert gas

cathode

600oC 5h, 15%H2

Porous anode

electrolyte anode Anode: 700 μm

0.71 cm2

Electrolyte surface

1.3 cm

~ 20μm Electrolyte Cathode: 20 μm

Towards a Sustainable Energy Future

2 μm

Fuel Cell Power Output H2, 3% H2O | fuel cell | Air

> 1 W/cm2 at 600°C!!! o

0.8

0.6

0.4

400

0.2

200

0.0

0 0

1000

2000

3000

-2

600 C 1000 o 550 C o 500 C o 445 C 800 o 400 C 600

Power density (mW.cm )

Voltage (Volts)

1.0

4000 -2

Current density (mA.cm ) Comparison: literature cathode material ⇒ 350 mW/cm2 at 600°C Towards a Sustainable Energy Future

Impact Cooler Material Boosts Fuel Cells

Z. Shao and S. M. Haile, “A High Performance Cathode for the Next Generation Solid-Oxide Fuel Cells,” Nature 431, 170-173 (2004).

SOFC cathode is hot stuff… Next generation of fuel cells…

Tech Research News R & D Focus Towards a Sustainable Energy Future

Fuel Cell Works

Summary & Conclusions • Sustainable energy is the ‘grand challenge’ of the 21st century – Solutions must meet the need, not the hype – Fuel cells can play an important role

• Solid acid fuel cells – Radical alternatives to state-of-the-art – Viability demonstrated; spin-off company established

• Solid oxide fuel cells – Promising alternative cathode discovered

• Still plenty of need for fundamental research “The stone age didn’t end because we ran out of stones.” -Anonymous Towards a Sustainable Energy Future

Learn More…

Towards a Sustainable Energy Future

The People • Current Students

Mikhail Chatr

Ayako

Drew

Mary

Kenji

Justin Áron

Evan

William

Tae-Sik

• Current Post-docs

• Former, who contributed to results Yoshi

Calum

Tetsuya

Dane

Zongping

Towards a Sustainable Energy Future

Jianhua

Marion

Wei Ali

Eric

Teruyuki