integrated micropower generator sossina m. haile, zongping shao, chan kwak, peter babilo california...

Integrated Micropower Generator

Sossina M. Haile, Zongping Shao, Chan Kwak, Peter Babilo

California Institute of Technology, Materials Science

Micro-SOFC

Swiss RollCombustor

+

High EfficiencyThermal Management

Integrated MicroPower Generator Review, Oct 18, 2002

Caltech Materials Science Tasks

1. Swiss Roll Optimization

2. Electrolyte Selection

3. Fuel Selection – with all others

4. (a) Anode Development - NWU

4. (b) Cathode Development

5. SCFC Model Development

6. Catalyst Optimization – with USC [later]

7. Stand Alone Swiss Roll Fabrication & Characterization

8. SCFC Fabrication – LBNL

9. First generation IMG Fabrication & Characterization

10. Evaluation and Redesign

11. Second Generation IMG Fab. & Characterization


SCFC Electrolytes

Oxygen Ion ConductorsDoped CeO2 (La,Sr)(Ga,Mg)O3

Proton ConductorsDoped Ba(Ce,Zr)O3 Doped SrCeO3

Anode

CH4 + ½ O2 CO + 2H2

H2 + O= H2O + 2e-

CO + O= CO2 + 2e-

Cathode½ O2 + 2e- O=

Chemical and Electrochemical Reactions

Electrolytes for 300-600C: 10-2 S/cm at 500C, tion ~ 1

Anode

CH4 + ½ O2 CO + 2H2

H2O + CO CO2 + H2

H2 2H+ + 2e-

Cathode½ O2 + 2H+ + 2e- H2O

H2O recirculation required with proton conductor


Electrolyte and Fuel Selection

Electrolyte

• Oxygen ion conductors

– Most literature demonstration based on such electrolytes

– Our initial investigations of proton conducting electrolytes were not promising

• Specific choice: doped CeO2

– Samaria doped (SDC)

– Excellent conductivity

– Good chemical stability

– Low electronic conductivity

– Experience with this material

Fuel• Choices

– Methane, ethane– Propane, butane– Alcohols

• Selection: Propane– Demonstrated in SCFCs– Only ethane gives

slightly higher power– Acohols very poor– Compatible with micro-

aspirator– Good vapor pressure

even at low temperature


Electrode Materials and Catalytic Activity

• Cathode

– Sr0.5Sm0.5CoO3 (SSC)

– SSC + SDC + Pt

– SDC + Pt

– La0.2Sr0.8Co0.6Fe0.4O3 (LSCF)

consider as catalyst instead

• Anode

– Ni + SDC

• Characterization

– Catalytic activity

– X-ray diffraction (stability)

– Fuel cell performane

C3H8 + O2

+ He or Ar

GC analysis

Thermocouple

Catalyst dispersed in inert materials

Catalytic Reactor

furnace


Gas Phase Reactivity

200 300 400 500 6000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

6

Yie

ld (

%)

Temperature (oC)

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Propane: 10ml/min, Oxygen: 50ml/min, Helium: 200ml/min

150 200 250 300 350 400 450 500 550 600 6500.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

6

Yie

ld (

%)

Temperature (oC)

-0.40.00.40.81.21.62.02.42.83.23.64.04.44.8

Empty reactor Silica granules, 1.5 g = inert dispersant

C3H8:O2 = 1:5; Stoichiometric combustion ratio

Note: C3H8:O2 = 1:1.5 is stoichiometric for partial oxidation


Catalytic Activity of Ni-SDC Anode Powder

Ni-SDC 0.2g

C3H8: 2 ml/min; O2: 3ml/min;

He 12 ml/min

300 400 500 6000

20

40

60

80

100

C3 O

2

Temperature (oC)

Co

nve

rsio

n (

%)

0

20

40

60

80

100

HC CO

2

CO

Yield

(%)

300 400 500 6000

20

40

60

80

100

C3 O

2

Temperature (oC)C

on

vers

ion

(%

)

0

20

40

60

80

100

HC CO

2

CO

Yield

(%)

C3H8:O2 = 1:1.5 C3H8:O2 = 1:3

Ni-SDC 0.2g

C3H8: 2 ml/min; O2: 6ml/min;

He 24 ml/min

[CO] as T , 35 – 45% yield at 500C; higher yield at lower O2


XRD Characterization of Anode Powder

20 30 40 50 60 70 80

NiO-SDC reduced under C3

NiO-SDC reduced under C3 & O2

NiNiO

NiO-SDC reduced under H2

NiO-SDC

Inte

nsi

ty

2-theta (degree)

20 30 40 50 60 70 80

NiO-SDC after reaction (C3:O2=1:3)

NiO-SDC after reaction (C3:O2=1:1.5)

NiNiO

NiO-SDC after reduction

NiO-SDC

Inte

nsi

ty

2-theta (degree)

• Ni-SDC after catalytic reactor testing– Ni is not reoxidized

• Pretreatment of the anode before fuel cell test (650C)– C3H8 & O2 cannot reduce NiO

– Pure C3H8 heavy coking

Brief H2 exposure


Catalytic Activity of (SSC) Cathode Powder

400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

SSC: 0.05gC

3H

8: 10ml/min

O2: 30ml/min

He: 120ml/min

CH4

CO2

C2H4

C2H

6

C3H8

CO

Yie

ld (

%)

Temperature (oC)

0

10

20

30

40

50

60

70

80

90

100

Pro

pane

con

vers

ion

(%)

400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

SSC: 0.05gC

3H

8: 1ml/min

O2: 3ml/min

He: 120ml/min

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

8

CO

Yie

ld (

%)

Temperature (oC)

0

10

20

30

40

50

60

70

80

90

100

400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70Based on O

2 balance

SSC: 0.05gC

3H

8: 10ml/min

O2: 30ml/min

He: 120ml/min Oxy

ge

n c

on

vers

ion

(%

)

CO2

CO H

2O

Yie

ld (

%)

Temperature (oC)

10

20

30

40

50

60

70

80

90

100

400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

Based on oxygen balance

SSC:0.05gC

3H

8: 1ml/min

O2: 3ml/min

He: 120ml/min

Oxy

ge

n co

nve

rsio

n (

%)

CO2

CO H

2O

Yie

ld (

%)

Temperature (oC)

0

10

20

30

40

50

60

70

80

90

100

1:3

1:3

Reactants concentrated

Reactant diluted


Catalytic Activity of SSC Cathode Powder

150 200 250 300 350 400 450 500 550 600 6500

3

6

9

12

15

18

21

24

27

30

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

6

CO

Yie

ld (

%)

Temperature (oC)

0

3

6

9

12

15

18

21

24

27

30

SSC:0.2gC

3H

8: 10ml/min

O2: 15ml/minHe: 200ml/min

150 200 250 300 350 400 450 500 550 600 6500

5

10

15

20

25

30

35

40

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

6

CO

Yie

ld (

%)

Temperature (oC)

-5

0

5

10

15

20

25

30

35

40

C3H

8: 10ml/min

O2: 50ml/min

He: 200ml/minSsC: 0.2g

150 200 250 300 350 400 450 500 550 600 6500

5

10

15

20

25

30

35

40

45

50

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

8

COYie

ld (

%)

Temperature (oC)

-5

0

5

10

15

20

25

30

35

40

45

50

SSC:0.2gC

3H

8: 1ml/min

O2: 5ml/min

He: 200ml/min

150 200 250 300 350 400 450 500 550 600 6500

3

6

9

12

15

18

21

24

27

30

Pro

pane

con

vers

ion

(%)

CH4

CO2

C2H

4

C2H

6

C3H

6

COYie

ld (

%)

Temperature (oC)

-202468101214161820222426283032

SSC: 0.2gC

3H

8: 1ml/min

O2: 1.5ml/min

He: 200ml/min

Reactants concentrated Reactants diluted1:5

1:1.5

1:5

Reactants concentrated Reactants diluted1:1.5


Characteristics of SSC Cathode Powder

• Some combustion at 350C

• Higher conversion as O2

• Erratic dilution dependence

• Higher conversion as T

• Not suitable at T >600C

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

Sm0.5

Sr0.5

CoO3, 900

oC calcined sample

After reaction, fresh sample

Cou

nts

(Lin

)

2-Theta (o)

Chemical stability by X-ray diffraction

SSC is stable under SCFC conditions(after catalytic reactor testing)

C3:O2 dilute conc. dilute conc.

1:5 17 9.4 46 40

1:3 13 14 39 80

1:1.5 11 10 31 30

Propane conversion %

500C 600C


Fuel Cell Performance Measurements

C3H8

O2

He

Keithley 2420

Thermocouple

FurnaceFuel cell

Anode Cathode

Electrolyte

GC analysis

Anode

Electrolyte

Bi-layer

double dry press

Co-sinter

Reduce

Bi-Layer

Cathode

Tri-layer

paint

Co-sinter

Cell Fabrication

Test Station• Cells examined

– [1] Ni-SDC | SDC | SSC

– [2] Ni-SDC | SDC | Pt-SDC

– [3] Ni-SDC | SDC | SSC-Pt-SDC

– 1500m | 40-60m | 50m

H2

Ar


SEM images of the double pressed cells

SDC

NiO-SDC

SSC

SDC

60 wt% NiO

20-40% porous

37 m

10 m

10 m

3 m


[1] Ni-SDCSDCSSC .

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

OC

V (

V)

O2/C

3H

8

0 40 80 120 160 200 2400.0

0.2

0.4

0.6

0.8

1.0

600 oC

400 oC

Current Density (mA/cm2)V

olt

age

(V)

0

10

20

30

40

50

60

Po

wer D

ensity (m

W/cm

2)

• OCV depends on O2:C3H8

– Optimum is 3:1

• Peak power density– At 600C, 48 mW/cm2

– At 400C, 28 mW/cm2

600C

Open circuit voltage Polarization curves

O2:C3 = 3:1

Hibino: 450C, 41 ml/min C3; 54 ml/min O2;

205 ml/min N2, 1.5mm SDC 240 mW/cm2

O2:C3H8 = 1.3:1 !!

C3: 10 ml/minHe: 240 ml/min


Cell Design Challenge

Ni+

SD

C

SS

C

SD

C

C3H

8, CO

, H2, O

2, H2O

C3H

8, CO

, H2, O

2, H2O

Inlet gases can sweep partial oxidation by-products to cathode side, lower cell voltage

Partial oxidation occurs on ‘edge’ of anode

C3H8+ O2

Ni+SDC

SSC

SDC

Coke formed primarily on leading edge of anode

C3H8 + H2O

CO + H2 + H2O + CO2


0 25 50 75 100 125 150 175 2000.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

Vol

tage

(V

olts

)

Pow

er d

ensi

ty (

mW

/cm

2 )

Current density (mA/cm2)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

475oCC

3H

8: 10ml/min

O2: 30ml/min

He: 120ml/min

0 25 50 75 100 125 150 175 200 2250.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

500oCC

3H

8: 10ml/min

O2: 30ml/min

He: 120ml/min

Pow

er d

ensi

ty (

mW

/cm

2 )

Vol

tage

(V

olts

)


02468101214161820222426283032

0 25 50 75 100 125 150 175 200 225 2500.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

525oCC

3H

8: 10ml/min

O2: 30ml/min

He: 120ml/min

Pow

er d

ensi

ty (

mW

/cm

2 )

Vol

tage

(V

olts

)


0

5

10

15

20

25

30

35

40

0 25 50 75 100 125 150 175 2000

5

10

15

20

25

30

35

40

45

Vol

tage

(V

olts

)

Pow

er d

ensi

ty (

mW

/cm

2 )


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

600oCC

3H

8: 10ml/min

O2: 30ml/min

He: 240ml/min

[2] Ni-SDCSDCPt-SDCO2:C3 = 3:1, reactants concentrated

less concentrated

475C

525C

500C

600C


400 450 500 550 600 650 700 7500.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 C

3H

8:10ml/min, O

2:30ml/min, He:120ml/min

C3H

8:10ml/min, O

2:30ml/min, He:240ml/min

OC

V (

volta

ge

s)

Temperature (oC)

• Strong impact of dilution on fuel cell performance• Even without SSC, Pt is better cathode than Ni• Optimal operation temperature ~550 – 600C

[2] Ni-SDCSDCPt-SDC

Less concentrated

Reactants

concentrated

625C

475C


400 450 500 550 600 650 700 7500

5

10

15

20

25

30

35

40

45

50

55

CH4

CO2

C2H

4

C2H

6

C3H

6

CO

Yie

ld (

%)

Temperature (oC)400 450 500 550 600 650 700 750

20

30

40

50

60

70

80

90

100

C3H

8

O2

Con

vers

ion

(%

)

Temperature (oC)

400 450 500 550 600 650 700 7500

2

4

6

8

10

12

14

16

18

CO H

2

H2O

Yie

ld r

ate

x104 (

mo

l/s)

Temperature (oC)

[2] Ni-SDCSDCPt-SDC

Outlet gas composition at open circuit

• C3H8: 10ml/min, O2: 30ml/min, He:

120ml/min (concentrated)

• At T > 625C– insufficient oxygen at cathode

– > 90% converstion

• At T < 475C– insufficient anode activity


0 10 20 30 40 50 60 70 800.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

550oC Pow

er

den

sity

(m

W/c

m2 )

Vol

tage

(V

olts

)


0

2

4

6

8

10

12

14

16

18

20

22

24

0 20 40 60 80 100 120 140 160 180 200 220 2400.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Po

we

r d

en

sity

(m

W/c

m2 )

Vo

ltag

e (

Vo

lts)


-10

0

10

20

30

40

50

60

70

600oC

0 20 40 60 80 100 120 140 160 1800.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

650oC Po

we

r d

en

sity

(m

w/c

m2 )

Vo

ltag

e (

Vo

lts)


0

10

20

30

40

50

A B

C

[3] Ni-SDCSDCSSC-Pt-SDC

• A and C: C3H8: 10 ml/min,

O2: 30 ml/min, He:120 ml/min,

• B: He: 240 ml/min

• Best power density : 68 mW/cm2

• SSC-Pt-SDC > SSC, SDC-Pt

• Stability depends on quality of (cathode) processing

O2:C3 = 3:1, reactants concentrated

O2:C3 = 3:1, reactants concentrated

O2:C3 = 3:1, less concentrated


Summary

• All fuel cells function only in a small temperature range (400-650C), otherwise OCV is nearly zero

• O2:C3H8 ratio had significant effect on the fuel cell

performance

– Optimal oxygen to propane ratio = 3:1

• Power density varied from several to ~ 70mW/cm2

– Maximum at 600C (initial) for Ni-SDC|SDC|SSC-Pt-SDC)

– SSC-Pt-SDC cathode preferable to SSC or SDC-Pt

• Carbon coking occurred only on the leading anode edge

• Fuel cell power stability depends on fabrication

– Occasional short circuit through electrolyte

– Delamination of cathode colloidal deposition, painting


Where to go from here

• Modification of Ni + SDC anode with Rh, Pd, Ru etc.

– Highly active catalysts for partial oxidation

– Initial results with Rh very promising

– Enable reduced temperature operation, ~ 400C– Task for Northwestern

• Design modifications

– Prevent/limit flow of partial oxidation products to cathode

– Together with Goodwin, LBNL group

• Cathode development

– Active oxygen reduction catalyst

– Inactive towards propane

– Initial results with Bi2V0.9Cu0.1O6- + Ag promising

integrated micropower generator sossina m. haile, zongping shao, chan kwak, peter babilo california...

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