Fuel Cells for a Sustainable Energy Futureaddis.caltech.edu/media/Associates 2007.pdfFuel Cells for...

Fuel Cellsfor a Sustainable Energy Future

Sossina M. Haile

Materials Science / Chemical EngineeringCalifornia Institute of Technology

Towards a Sustainable Energy Future

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…


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


World Energy Consumption

2005 totals: 490 Q-Btu, 515 EJ, 16TW2030 projections: 720 Q-Btu, 760 EJ, 24TW

86% fossil

81%

Year1980 1990 2000 2010 2020 2030

Ene

rgy,

Qua

drill

ion

BTU

0

50

100

150

200

250

Exa

Jou

les

(1018

)

0

52

104

156

208

260

Equi

vale

nt P

ower

(TW

, 1012

)

0

2

4

6

8History Projections Oil

Coal

Natural Gas

HydroelectricNuclear

Total Renewables

Other Renewables

Source: US Energy Information Administration


Fossil Fuel Supplies

0.0E+00

5.0E+04

1.0E+05

1.5E+05

2.0E+05(E

xa)J

OilRsv

OilRsc

GasRsv

GasRsc

CoalRsv

CoalRsc

UnconvConv

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

30027032Coal

18 - 657 – 4011 - 25Gas

23 - 5510 – 3513 - 20Oil

Total, yrsResources, yrsReserves, yrsSource

> 400 yrs

56-77 287-345

Source: US Energy Information Administration


Reserves History for American Coal

0

500

1,000

1,500

1920 1960 2000

Res

erve

s, G

t

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

Paul Averitt (USGS)2,136 years

1,433 yearsBureau of Mines/EIA

(based on Paul Averitt’s surveys)

368 years 270 years 236 years

Courtesy: David Rutledge

“Hubbert Peak” type of analysis suggests 90% depletion by 2076


US Energy Imports/Exports: 1949-2004

1957: Net Importer

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

Total

Coal

Petroleum

Total

Petroleum

Net

Imports ExportsSource: US Energy Information Administration

1950 1960 1970 1980 1990 2000 1950 1960 1970 1980 1990 2000

1950 1960 1970 1980 1990 2000

Qua

d B

TU

353025201510

50

6

5

4

3

2

1

0

Qua

d B

TU

Qua

d B

TU

35

30252015105

0


Environmental Outlook

year1000 1200 1400 1600 1800 2000

atm

osph

eric

CO

2 [p

pm]

270

280

290

300

310

320

330

340Global CO2 levels

Source: Oak Ridge National Laboratory

2006: 382 ppm

Projections:

500-700 ppm by 2020

• Anthropogenic– Fossil fuel (75%)– Land use (25%)

Industrial Revolution


Environmental Outlook

Intergovernmental Panel on Climate Change, 2001; http://www.ipcc.chN. Oreskes, Science 306, 1686, 2004; D. A. Stainforth et al, Nature 433, 403, 2005

- 8

- 4

0

+ 4

400 300 200 100

Thousands of years before present (Ky BP)

0

ΔTre

lati

ve t

o pr

esen

t (°

C)

300

400

500

600

700

800

CH4(ppmv)

-- CO2

-- CH4-- ΔT

325

300

275

250

225

200

175

CO2(ppmv)

CO2 in 2006: 382ppmv


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


Greenland Ice Sheet Melt Extent


More Observations of Global Climate Change

Coral Bleaching

Grinnell Glacier and Grinnell LakeGlacier National Park

1910

1977


Future Scenarios

Most optimitistic scenario Centuries for CO2 to decay

Courtesy: John Seinfeld


Future Scenarios

Highly optimitistic scenario: stabilize at 380 ppm

(aerosols)


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


The Energy Solution

Solar1.2 x 105 TW at Earth surface

600 TW practical

Biomass5-7 TW grossall cultivatable land not used

for food

HydroelectricGeothermal

Wind2-4 TW extractable

4.6 TW gross1.6 TW technically feasible0.9 TW economically feasible0.6 TW installed capacity

12 TW gross over landsmall fraction recoverable

Tide/OceanCurrents2 TW gross

The need:~ 20 TW by 2050

Fossil with sequestration1% / yr leakage -> lost in 100 yrs

NuclearWaste disposal

60 yr uranium supply


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


Caltech Center for Sustainable Energy Research

H2O, CO2

Photovoltaic and photolysis power plants

Fuel: H2 or

CH3OHFuel cell

power plant

Electric power,heating

Electricity

H2O, CO2

Conversion

Utilization

Storage

Harry AtwaterHarry GraySossina HaileNathan Lewis


Fuel Cells: Part of the Solution?

• High efficiency

– low CO2 emissions

• Size independent

• Various applications

– stationary

– automotive

– portable electronics

• Controlled reactions

– “Zero Emissions”

• Operable on hydrogen

– (if suitably produced)

power plant size [MW]0 5 10 15 20 25

effic

ienc

y [

%]

0

20

40

60

80

Fuel Cells

Combustion Engines

automotive engine: 50-75 kW

*Can be as high as 80-90% with co-generation

*


Anode Cathode

Fuel Cell: Principle of Operation

H2 O2H+

Overall: H2 + ½ O2 → H2O

½ O2 + 2H+ + 2e- → H2OH2 → 2H+ + 2e-

conversion device, not energy source

best of batteries, combustion engines

Electrolyte

e-


Fuel Cell Performance

H2 + ½ O2 → H2O1.17 Volts (@ no current)

• voltage losses

– fuel cross-over

– reaction kinetics

– electrolyte resistance

– slow mass diffusion

• power = I*V

• peak efficiency at low I

• peak power at mid I Current [A / cm2 ]

0.0 0.4 0.8 1.2 1.6

Vol

tage

[V

]

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Pow

er [W

/ cm

2 ]

0.0

0.2

0.4

0.6

0.8theoretical voltagecross-over

slow reaction kinetics

electrolyteresistance

slow massdiffusion

peak power


Fuel Cell Types

O2O2 + CO2O2O2 + H2OO2Oxidant

Y-ZrO2

O2- ↑Na2CO3

CO32- ↑

H3PO4

H+ ↓KOHOH- ↑

NafionH3O+ ↓

Electrolyte

Ion

HC + COHC + COH2H2H2 + H2OFuel

SOFC700-1000

MCFC500-700

PAFC150-220

AFC100-250

PEM90-110

Type°C

Types differentiated by electrolyte, temperature of operation

Portable Stationary

Fuel flexibility, efficiency Easy thermal cycling

Target regime

⌧Corrosive liquids


New Electrolytes: Solid Acids

• Chemical intermediates between normal salts and normal acids: “acid salts”

½(Cs2SO4) + ½(H2SO4) → CsHSO4

• Physically similar to salts

• Structural disorder at ‘warm’ temperatures

• Properties

disorderedstructure

normal structure

structuraltransition

1/TT

log(

cond

uctiv

ity)

.

polymer

Direct H+ transport

Humidity insensitive

Impermeable

Water soluble!! Brittle


Proton Transport Mechanism

Sulfate groupreorientation

10-11 seconds

Proton transfer

10-9 seconds

H

O

S


Fuel Cell Operation

0.0 0.5 1.0 1.5 2.00.0

0.2

0.4

0.6

0.8

1.0

1.2

Vol

tage

( V

)

Current density ( A / cm2)

0.0

0.1

0.2

0.3

0.4

0.5

36 μm electrolyte

100 sccm 200 sccm

Pow

er d

ensi

ty (

W /c

m2 )

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

H2, H2O | cell | O2, H2O

T = 248°C8 mg Pt/cm2

10-40 μm pores, ~40% porosity

Slurry deposit

Fine CsH2PO4

2 μm

Open circuit voltage: 0.9-1.0 V Peak power density: 285-415 mW/cm2


Impact

Some Like It Medium Hot

The promise of protonics Solid Acids Show Promise...

Nature: News & ViewsScience Now Magazine

Physics Today Online

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).


From Breakthrough to Product

2001

1 cm2 of fuel cell area

36 mg Pt for 10 mW

43 g Pt for 60 W bulb

~ $9,000 in Pt

1 mg Pt for 200 mW

2.5 g Pt for 60 W bulb

~ $100 in Pt

2007

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

MVI_1924.avi

Calum

Dane


New Cathodes for Solid Oxide Fuel Cells

• Traditional cathodes– A3+B3+O3 perovskites– Poor O2- transport– Limited reaction sites

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

electrolyteO2-

O2

Oad2e-

cathodeOad

electrolyteO2-

O2 Oad 2e-cathodeO2-

‘triple-point’ path electrode bulk path

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

almost 1 in 4 vacant


Cell Fabrication

Spray cathode

NiO + SDC(Ce0.85Sm0.15O2)

NiO + SDC

SDC

Dual dry press

Sinter,1350oC 5h

600oC 5h, 15%H2

Porous anode

Calcine, 950oC5h, inert gascathode

electrolyte

anode

Anode: 700 μm

Cathode: 20 μm

Electrolyte

~ 20μm

Electrolyte surface

2 μm

1.3

cm

0.71 cm2


0 1000 2000 3000 40000.0

0.2

0.4

0.6

0.8

1.0

0

200

400

600

800

1000

Pow

er d

ensi

ty (m

W.c

m-2)

Vol

tage

(Vol

ts)

Current density (mA.cm-2)

600oC 550oC 500oC 445oC 400oC

Fuel Cell Power Output

> 1 W/cm2 at 600°C!!!H2, 3% H2O | fuel cell | Air

Comparison: literature cathode material ⇒ 350 mW/cm2 at 600°C


Impact

Cooler Material Boosts Fuel Cells

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

Tech Research News

R & D FocusFuel Cell Works

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


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


Learn More…


The People• Current Students

Calum DaneTetsuya

MaryKenji

Zongping

Justin

Wei

• Former, who contributed to results

• Current Post-docs

Drew

William

AyakoChatr

Áron Evan Tae-Sik

Mikhail

MarionJianhuaYoshi

TeruyukiEricAli

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