Solid Oxide Fuel Cells:Science, Technology, and Applications, gy, pp

S David Dvorak Ph D PES. David Dvorak, Ph.D, P.E.

20 June 2008

Summer School on ‘Materials for the Hydrogen Economy’

Reykjavik, Iceland

Outline

• Characteristics and Basic Operation• Multifuel Capability• Multifuel Capability• Cell Designs

l• Materials• Performance• Applications• High Temperature ElectrolysisHigh Temperature Electrolysis

2

Characteristics of SOFC Systems

• Multifuel capability with minimal gas cleanupMultifuel capability with minimal gas cleanup

• High quality exhaust heat

• Good reaction kineticsGood reaction kinetics

• High power density

• Slow startup / response time• Slow startup / response time

• Materials issues

• Thermal cycling issues• Thermal cycling issues 

• Sealing issues

3

SOFC: Basic Operation

Anode Reaction: Cathode Reaction:

H + O2‐→ H O + 2e‐ ½ O2 + 2e‐ → O2‐O ll R ti

4

H2 + O → H2O + 2e ½ O2 +  2e → OOverall Reaction:

H2 + ½ O2 → H2O

Multifuel Capability

• Hydrocarbon  Reforming

– CnHm + nH2O→ (n + m/2)H2 + nCOn m 2 ( / ) 2

• Coal Gasification

– C + H2O→ H2 + CO • Biomass Gasification:

– (C6H10O5)n + 7nH2O → 6nCO2 + 12nH2

• Carbon Deposition:

Methane Pyrolysis CH + H O→ C + 2H– Methane Pyrolysis CH4 + H2O→ C + 2H2

– Boudouard disproportination 2CO → C+ CO2

– Reverse Gasification      CO + H2 → C + H2O2 → 2

5

Anode Reactions: Hydrocarbon Fuelsy

• Steam Reformation  of Methane:

– CH4 + H2O→ 3H2 +CO          ΔHo = 206 kJ/mole

W t G Shift• Water Gas Shift:

– CO + H2O→ H2 + CO2  ΔHo = ‐36 kJ/mole

• Oxidation Reactions:

– Hydrogen     H2 + O2‐→ H2O + 2e‐y g 2 2

– Carbon Monoxide  CO + O2‐→ CO2 + 2e‐

6

Enthalpy and Entropy For Hydrogen Oxidation

( ) ( )T

0H T H T dTΔ Δ ∫

H2 + ½O2 → H2O

( ) ( ) ( )H T H T H TΔ Δ Δ∑ ∑ ( ) ( )0

0f f p

T

H T H c T dTΔ = Δ + ∫

( ) ( )Tp0 c T

S T S dT= + ∫

( ) ( ) ( )f fProducts Reactants

H T H T H TΔ = Δ − Δ∑ ∑

( ) ( ) ( )S T S T S TΔ = −∑ ∑ ( )0T

S T S dTT

= + ∫( ) ( ) ( )Products Reactants

S T S T S TΔ ∑ ∑

-200 0

-240

-220

py (k

J/m

ol)

-100

-50

py (J

/mol

-K)

-300

-280

-260

Enth

al

-200

-150Entro

p

7

300 400 500 600 700 800

Temperature (K)

300 400 500 600 700 800

Temperature (K)

Gibbs Free Energy and Thermodynamic Potential (E) as functions of temperature

H + ½O → H O

ΔG = ΔH - TΔSGE

2FΔ

= −

H2 + ½O2 → H2O

2F

-200

-190

J/m

ol)

1.25

1.30

ge-220

-210

Free

Ene

rgy

(kJ

1.10

1.15

1.20

sibl

e C

ell V

olta

g

-240

-230

300 400 500 600 700 800

Gib

bs F

1.00

1.05

300 400 500 600 700 800

Rev

ers

8

Temperature (K) Temperature (K)

SOFC Thermodynamicsy

1 40

1

1.2

1.4

‐100

‐50

0

Gibbs

0.6

0.8

1

‐200

‐150

100 Gibbs

Enthalpy

E

(kJ/mol)

ntial (Vo

lt)

0.2

0.4

0.6

‐300

‐250

200

Energy 

Pote

0‐350

300 400 500 600 700 800 900 1000 1100 1200

9

Temperature (K)

Temperature Effects

• An increase in temperature – reduces the thermodynamic potential – Improves electrode kinetics– Increases ionic conductivity of electrolyte

10Kordesch & Simader, Fuel Cells and Their Applications, VCH, 1996

Cell Designs

• Tubular DesignL P D it

• Planar DesignHi h P D it– Lower Power Density

– Easier to seal

– Higher Power Density

– Harder to Seal

11

Planar Cell Configurations

• Electrolyte Supported Cells (ESC)

g

ANODE

– Thick electrolyte (120μm)– 800oC ‐1000oC

• Anode Supported Cells (ASC)

ELECTROLYTE

CATHODE

Anode Supported Cells (ASC)– Anode 0.6mm thick– 600oC ‐900oC– Thin electrolyte (higher ionic

ANODE

ELECTROLYTE– Thin electrolyte (higher ionic conductivity at lower temperatures

• Porous Metal Substrate Cells (PMSC)Corrosion resistant ferretic stainless steel

CATHODE

ANODEELECTROLYTE– Corrosion resistant ferretic stainless steel 

(0.5 to 1 mm)– 600oC ‐700oC– Thin Electrolyte (3YSZ) ( 2 – 4 μm)

ELECTROLYTECATHODE

SUBSTRATE

– Thin Electrolyte (3YSZ) ( 2 – 4 μm)

12

Tubular Cell Developmentp

Siemens Power Group

• Circular to flattened tubes(HPD5)

• Corrugated Delta9 cell (500mA/cm2)g ( / )

13

SOFC Stack Performance

0.44 A/cm2 @ 0.69V0.3 W/cm2

14

SOFC materials

• Severe material environmentSevere material environment

– Chemical stability

– Mechanical StabilityMechanical Stability

– Microstructural Stability

• Electrolyte• Electrolyte

• Anode

• Cathode• Cathode

• Interconnect

15

SEM Image: Electrolyte Supported Cell

Cathode →

Electrolyte →

Anode →

• Anode Nickel Oxide / YSZ Cermet• Electrolyte 8YSZ (8% Yttria Stabilized Zirconia)• Cathode: Lanthanum Strontium Manganite (LSM) L S M OLa0.6Sr0.4MnO3

16

SEM Image: Anode Supported Cell

• Anode support structure (Ni / 8YSZ cermet) 600μm

• Anode functional layer (Ni / 8YSZ) 10μm

• Electrolyte (8YSZ) 5μm• Electrolyte (8YSZ) 5μm

• YDC Intermediate Layer (Ce0.8Y0.2O1.9) 3μm :

– Prevents the formation of low‐conducting phase at YSZ/LSCF interface

• LSCF (La0.6Sr0.4Co0.2Fe0.8O3) Cathode  25μm

17Reference: www.ecn.nl

SOFC Applications

• SOFC Technology is scaleable over a wide range of power requirements

pp

requirements:

– Portable Power (20W – 1.5kW)

Auxiliary Power (5kW 10kW)– Auxiliary Power (5kW – 10kW)

– Combined Heat and Power (CHP) (2kW – 10kW)

– Stationary Power (25kW – 250kW)– Stationary Power (25kW – 250kW)

• SOFC Systems are applicable where there is a need for:SOFC Systems are applicable where there is a need for:

– Fuel Flexibility

– High quality waste heatHigh quality waste heat

18

SOFC Applications:Portable Power

• 250 Watt Battery Charger• 250 Watt Battery Charger, – Kerosene fuel

T b l ll d i– Tubular cell design

– 15,2 x 25,4 x 30,5 cm

19www.mesoscopic.com,  www.toto.co.jp

SOFC Applications: Auxiliary Powerpp y

• In the US, idling trucks consume about one billion gallons of fuel annuallyof fuel annually  

• SOFC APU systems providing heat and electrical power could cut fuel used while idling by 85%

DELPHI 5 kW APU Stack

f• CPOX Reformer• Cathode Air HEX

• 30 cells (two per APU)• 9 kg, 2.5 liters 20www.greencarcongress.com

SOFC Applications:Combined Heat and Power

• Partnership between Dantherm, Htceramix

Combined Heat and Power

Partnership between Dantherm, Htceramix

• System designed around 1kW integrated SOFC module (HotBox™)( )

21

www.leblogenergie.com

SOFC Co-Generation: Example

• 109 kW Electricity

• 69 kW of hot water for district heatingg

• Operated on natural gas in Netherlands and Germany for 20.000 hours

22www.powergeneration.siemens.com

SOFC / Gas Turbine Hybrid: S t S h tiSystem Schematic

• Produces steam and power23

Thermodynamic Efficiency

Reversible Thermodynamic Efficiency

GΔCarnot Cycle Efficiency 

LT1thermo

GH

Δε =

ΔL

carnotH

1T

ε = −

8090

100

8090

100

4050

6070

Effi

cien

cy [%

]

Max Efficiency (LHV)4050

6070

Effi

cien

cy [%

]

Max Efficiency (LHV)

010

2030

E Max. Efficiency (LHV)Carnot Limit

010

2030

E Max. Efficiency (LHV)Carnot Limit

24

00 200 400 600 800 1000

Temperature [degC]

00 200 400 600 800 1000

Temperature [degC]

Efficiency of SOFC/GT Hybrid Systemsy y y

25

SOFC / Gas Turbine Hybrid: Example

220 kW Proof of Concept Demonstrator• 200 kW from SOFC stack• 20 kw from microturbine• Operated  at the National Fuel Cell Research Center, 

Irvine CA for 3500 hours with 53% electrical efficiencyIrvine, CA, for 3500 hours with 53% electrical efficiency

26www.powergeneration.siemens.com

Future Gen, integrated Hydrogen, Power Production, d C b S t ti R h I iti ti

• Goals (2020)

and Carbon Sequestration Research Initiative

– Design , construct, and operate a 275 MW power plant that produces electricity and hydrogen with near zero emissionsemissions

– Produce electricity at only 10% more than non‐sequestered power plant

– Produce hydrogen at $0.48/kg

• Key features:

– Coal gasification produces syngas (H2, CO, CO2, H2O,  . . .)

– Hydrogen separated out of syngas, compressed

D l t d d f l f SOFC / GT H b id t– Depleted syngas used as fuel for SOFC / GT Hybrid system

– Use of ion conducting ceramics for H2, O2 separation 27

FutureGen Simplified Process Flow Diagram

28Williams, et. Al. J. Power Sources 159 (2006) 1241 ‐ 1247

High-Temperature Electrolysis (SOEC)g p y ( )

Electron Flow

H2

e_

O2

OxygenHydrogen

Electron Flow

O2-

H2O

WaterOxygen Ions

Water

Cathode Electrolyte AnodeAnode Reaction:Cathode Reaction:

H2O + 2e‐ → H2 + O2‐ O2‐ → ½ O2 +  2e‐Overall Reaction:

29

2 2 2Overall Reaction:

H2O→ H2 + ½ O2

Electrolyzer and Fuel Cell Performance

2.5

2.0

e

1.0

1.5

Cel

l Vol

tage

Electrolyser CellFuel Cell

0.5

1.0C

0.00 1 2 3 4

30

Current Density [A/cm2]

Energy Demand for Water and Steam Electrolysis

• Energy needed to electrolyze water:  ∆H = ∆G + T ∆S

• At high temperatures, the addition of heat (T∆S) reduced the electricity needed (∆G) for electrolysis

31Mingyi, et. Al., J. Pwr. Sources 2008

Conventional Water Electrolysis: Energy Flow Diagrams

32Donitz, et. Al., Int. J. Hydrogen Energy 13 (5) 283 – 287, 1988 

High Temperature Water Electrolysis: E Fl Di

• “Hot Elly” autothermal operation

Energy Flow Diagrams

• “Hot Elly” with additonal high‐temperature heat

33

High Temperature Electrolysis

• At 800 – 1000oC the electrical energy required to lit t i d d b b t 25%

g p y

split water is reduced by about 25%

• In addition to thermodynamic effectgs, improved electrode kinetics red ce req ired oltageselectrode kinetics reduce required voltages

• System complexity and materials issues remain serious challengesserious challenges.

34