Catalyst Material Development for Internal Reforming SOFC Fuelled by Sustainable Biofuels

Kyushu University, Department of Mechanical EngineeringInternational Institute for Carbon-Neutral Energy Research (I2CNER)

Next-Generation Fuel Cell Research Center

Yusuke Shiratoriy-shira@mech.kyushu-u.ac.jp

2nd International Symposium on Solid Oxide Fuel Cells for Next Generation Power Plants

Imperial College London, Friday 19th April, 2013

2

Research background

3

Solid oxide fuel cell (SOFC)

Solid electrolyte

O212

H2, CO

H2O, CO2

2e-

2e-Anode (Ni-YSZ)

Cathode (LSM-YSZ)

Hydrocarbon(Chemical energy )

Air

Reforming

O2-

Anode contains excellent reforming catalyst, Ni.

All solid materials

Compact design is possible.

Practical fuels such as city gas, natural gas, biogas, biodiesel, gasoline and alcohol, etc., can be supplied directly to SOFC.

Operation mechanism of direct internal reforming SO FC

In principle, possiblePractically, chemical andthermomechanicalproblems will arise！

Direct Internal reforming SOFC

（DIRSOFC）

Direct Internal reforming SOFC

（DIRSOFC）

Internal reforming can occur.Internal reforming can occur.

High temp. operation in the temp. range between 600 and 900 °C

High temp. operation in the temp. range between 600 and 900 °C

Electricity

Problems in conventional DIRSOFC

4

790 ppm H2S

CH4

62.6 %

CO2

35.7 %

H2

99 ppm

N2

0.09 %

H2

O 1.62 %

H2

S < 0.5 ppm

Desulfurizer(FeO pellets)

Y. Shiratori, T. Ijichi, T. Oshima, K. Sasaki, “Internal Reforming SOFC Running on Biogas”, International Journal of Hydrogen Energy 35 (2010) 7905-7912.

Field test of internal reforming SOFC running on bi ogas

After test with real biogas

Severe cokingSevere coking

5

0 100 200 300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0

1.2

Cel

l vol

tage

/ V

Time / h

Temp: 800 oCCurrent density: 200 mA cm-2

Real biogas(1.4 < CH4/CO2 < 1.7, H2S ≈ 0.2 ppm)

Simulated biogas(CH4/CO2 = 1.5)

Methane fermentation reactorPlace: Tosu-city, Saga, JapanReactor size: 144 m3

Biogas: Max 250 m3 / dayOutput: Max 60 kW level

Desulfurized biogas

Long term test of DIRSOFC with anode-supported button cell

Direct feed of biogas to SOFC is feasible!

Saga Prefecture

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

16

18

Time / h

CO formation

Rea

ctio

n ra

tes

/µm

ols-

1cm

-2

1 ppm H2S1 ppm H2S

Temp: 1000 oCFuel: Simulated biogas mixture (CH4/CO2 = 1.5)Cell type: Electrolyte-supported (Ni-ScSZ/ScSZ/LSM-ScSZ)Current density: 200 mA cm-2

0 2 4 6 8 10 12 14 16 18 200.0

0.2

0.4

0.6

0.8

1.0

1.2

Cel

l vol

tage

/ V

Time / h

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Vol

tage

loss

es /

V

Anodic overvoltage

Anode-side IR drop

Cell voltage

CH4 consumption

CO2 consumption

100 mV, 9 % of initial cell voltage

40 % decrease

1 h

Y. Shiratori, T. Oshima, K. Sasaki, “Feasibility of Direct-biogas SOFC”, International Journal of Hydrogen Energy 33 (2008) 6316-6321.

Deactivation of anode by 1 ppm H 2S measured at 1000 oC

Electrochemical deactivation Catalytic deactivation

6

R1━COOCH3

R2━COOCH3

R3━COOCH3

CH2━COO━R1

┃

CH━COO━R2

┃

CH2━COO━R3

3CH3OH

CH2━OH ┃

CH━OH┃

CH2━OH

+ +→

Fatty oil MethanolFatty Acid Methylester(FAME)⇒⇒⇒⇒ BDF Glycerol

Biodiesel fuels

Name Formula Degree of unsaturation

Composition / wt %

Palm Jatropha SoybeanWaste-cooking

Discarded fish

Palmitic acid methyl ester C17H34O2 0 39.9 13.7 10.7 34.9 27.2

Stearic acid methyl ester C19H38O2 0 4.35 6.65 3.19 4.51 7.52

Oleic acid methyl ester C19H36O2 1 40.4 40.5 22.4 36.9 35.4

Linoleic acid methyl ester C19H34O2 2 12.0 31.5 53.9 8.9 8.8

Linolenic acid methyl ester C19H32O2 3 0.21 0.17 5.28 0.31 0.44

Tri-glyceride 0.4 0,4 0.1 6 6

Sulfur S 1ppm 7ppm ≦1ppm 3ppm 8ppm

7

BDFs derived from Palm, Jatropha, Soybean, Waste-cooking, Discarded fish oils

8

Measured compositions of anode off-gas for the internal steam reforming of practical-BDFs (soybean- , jatrropha- and palm-BDF ) and reference FAMEs (oleic- and linoleic-FAME ) on Ni-ScSZ anode

(a) 800 oC

H2

CO

CO2

CH4

C2H4

0 5 10 15 20 50 55 60 65 70 75

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Equilibrium

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Equilibrium

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Equilibrium

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Concentration in anode off gas / %

0 5 10 15 20 50 55 60 65 70 75

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Equilibrium

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Equilibrium

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

Equilibrium

Oleic-FAME

Jatropha-BDFPalm-BDF

Soybean-BDF

Linoleic-FAME

0 5 10 15 20 50 55 60 65 70 75

(b) 700 oC

0 5 10 15 20 50 55 60 65 70 75

Concentration in anode off gas / %

H2

CO

CO2

CH4

C2H4

Internal steam reforming of biodiesel

SOFC

Methane fermentation

Test cell simulating real SOFC

We demonstrated “Generation of electricity from garbage” and “Generation of electricity from vegetable oils” using lab-scale solid oxide fuel cell.

DIRSOFC running on biofuels

Biogas Palm-biodiesel

“Visualization of SOFC in operation”

in

Local cooling caused by endothermic reforming

out

Biofuels

① Crack formation

Operating temp.: 800 oCCurrent density: 0.2 A cm-2

Time / h0 200 400 600 800

Cel

l vol

tage

/ V

0.0

0.2

0.4

0.6

0.8

1.0Biogas

Palm-BDF

are pronounced at the cooled area.

Y. Shiratori et al., Int. J. Hydrogen Energy 35 (2010) 7905-7912.

I. Feasibility study-Efforts toward the realization of DIRSOFC running on biofuels-I. Feasibility study-Efforts toward the realization of DIRSOFC running on biofuels-

II. Practical study-Clarification of thermomechanical problems in the internal reforming operation-II. Practical study-Clarification of thermomechanical problems in the internal reforming operation-

“Direct Internal reforming SOFC running on biofuels”

Button cell operation was possible.Rather high degradation rate due to

coking on the anodeBiogas ：：：： ~3.0%/1000h

Palm-BDF ：：：： ~15%/1000h

Button cell test

② Impurity poisoning ③ Carbon deposition5

mm

Crack in dense electrolyte

①

5 mm

Ni dust

NiScSZ C

③

Cel

l vol

tage

/ V

1 ppm H 2S

0 2 4 6 8 10 12 14 16 18 20 220.0

0.2

0.4

0.6

0.8

1.0

1.2

Time / h

Cell voltage

Fuel: BiogasOperating temp.: 800 oCCurrent density: 0.2 A cm-2

②

Blockage of diffusion path by deposited carbon

Previous studies 9

Direct internal reforming operation is currently impossible.

Temperature homogenization in the cell is necessary!

10

Development of flexible catalyst material“Paper-structured catalysts (PSCs)”

11Microstructure of paper-structured catalyst (PSC)

YSZ fiber (Zf)

Ni or Ni-MgO

Inorganic binder（Al2O3 (As) or ZrO2 (Zs) or CeO2 (Cs))

Al2O3 fiber (Af) SiO2-Al2O3 fiber (Cf)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.01 0.1 1 10 100 1000

dV/ d

(logD

)/ c

m3

g-1

Pore diameter / µm

ZfCfZs paper

Cermet anode

Compacted powder

5 µm

Ni

ScSZConventional anode

Pore diameter: 1 µmPorosity: 32 %

Conventional cermet anode （（（（Ni-ScSZ））））

Flexible fiber network

50 µm

Paper-structured catalyst

Pore diameter: 17 µmPorosity: 83 %

Paper-structured catalyst (PSC)

12

H2

N2

H2O

MFC

Reactor

BDF

Evaporator

Upper furnace

Lower furnace

800 oC

600 oC

MFC

6 µl min-1

21 µl min-1

50 ml min-1

150 ml min-1

S/C = 2.0-3.5

Micro pump

Micro pump

Water trap

Gaschro

2 PSCs

T.C. was placed between the two papers.

Data logger

20 mm

T.C.

Fuel(simulated biogas)CH4 : CO2 = 1 : 1

Off-gas

800 or 750 oC

Paper-structured catalyst

to GC

Experimental setup for biofuel reforming

Dry reforming of methane Steam reforming of BDF

♦ CH4 conv.♦ H2 production rate♦ CO production rate♦ Temp. decrease

13Performance of PSC for dry reforming of methane

♦ Simple processing♦ Easy handling♦ High catalytic activity♦ Catalytic function easily adjustable ♦ Applicable to various devises♦ Available under SOFC operating condition♦ Tolerant to thermal shock

Features of PSCComparison with conventional anode

Paper-structured catalyst (PSC) exhibited

considerably higher catalytic activity than

that of conventional SOFC anode.

0.0

0.2

0.4

0.6

0.8

1.0

Conversion

and selectivity / -

Equilibrium at 800 o

C

Ni-YSZ anode support （200 mA cm-2

） at 800 o

C

（W/F = 8.4 g-cat h mol-1

）

PSC at 800 o

C (W/F = 0.17 g-cat h mol-1

)

Fuel: simulated biogas （CH4

/CO2

= 1)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.80.0

0.2

0.4

0.6

0.8

1.0

1.2

Current density / A cm-2

Cel

l vol

tage

/ V

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Pow

er d

ensi

ty /

Wcm

-2

14

2 cm

Self-made anode-supported cellPSC

Biogas

Ni-MgO/ZfCfZsAnode support: Ni-YSZ Electrolyte: YSZ

CH4/CO2= 1

45 %LHV (at Uf = 78 %)

Performance of DIRSOFC fuelled by simulated biogas

Temp. : 750 oCFuel : CH4/CO2 = 1Current density : 200 mA cm-2

Uf: 14 %

♦ Maximum power density of 820 mW cm-2

♦ Degradation rate of 1.4 %/1000 h♦ No coking

Temp. : 750 oCFuel : CH4/CO2 = 1

15

Molecular formula

Degree of unsaturation

wt %

Palmitic acid C17H34O2 0 39.9

Stearic acid C19H38O2 0 4.35

Oleic acid C19H36O2 1 40.4

Linoleic acid C19H34O2 2 12.0

Linolenic acid C19H32O2 3 0.21

Tri-glyceride 0.4

Sulfur S 1ppm

Palm oil-BDF

0 10 20 30 40 50

50

60

70

80

H2

conc

entr

atio

n / %

Ni-MgO/ZfAfAs

Fuel: Palm BDF (S/C = 3.5)Temp: 800 oCGHSV = 3900 h-1

Time / h

Ni/ZfAfZswith MgO

Ni only

45

55

65

75

0

1

2

3

4

5

Ni-MgO/ZfAfZs

Ni-MgO/ZfAfCs

C2H

4co

ncen

trat

ion

/ %

♦ Ni loaded PSC exhibited insufficient catalytic activity for steam reforming of BDF, deactivated rapidly accompanied by the formation of C2H4.♦ MgO addition was quite effective to improve catalytic activity.♦ Choice of inorganic binder is very important to achieve stable performance.♦ Ni-MgO loaded PSC using CeO2 sol as an inorganic binder, Ni-MgO/ZfAfCs, can stably convert palm-BDF to produce H2.

Performance of PSC for the steam reforming of BDF

S/C = 3.5

O0 20 40 60 80 100

0

20

40

60

80

100

H

0

20

40

80

100

C

Carbon deposition

region

S/C = 3.0S/C = 2.0

S/C = 0

Oleic-FAME (C19H36O2)

Oleic-FAME(C19H34O2)+ steam + N2

Ni-MgO loaded PSC

Perovskite containing PSC

20 mm

800 oC

Evaporator

dry air

H2, CO, CO2, CH4C2H4 and steam

600 oC

PSC

800 oCSOFC

16Experimental setup for BDF fuelled SOFC

Ni-YSZ anode-supported cell

0.0 0.2 0.4 0.6 0.8 1.0 1.20.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Cel

l vol

tage

/ V

Current density / A cm-2

Oleic-FAME , (S/C = 2.0)

Palmitic-FAME /Oleic-FAME = 1 (S/C = 2.0)

Temp.: 800 oC

with PSC

with PSCPalm-BDF(S/C = 3.5)

17

IV curves in the feed of biodiesel fuels

Performance of SOFC fuelled by biodiesel

without PSC

Palmitic-FAME (C16:0)

Oleic-FAME (C18:1)

♦ By applying PSC, quite large current density of above 1.0 A cm-2 was obtained at 0.7 V.

♦ The addition of saturated FAME, here palmitic FAME, had the positive impact on the cell performance due to the suppression of C2H4 formation.

0 10 20 80 90 1000.5

0.6

0.7

0.8

0.9

1.0

Cel

l vol

tage

/ V

Time / h

without PSC (S/C = 3.5)

Temperature: 800 oCFuel: Oleic-FAMECurrent density: 0.2 A cm-2

with PSC (S/C = 2.0)

Degradation rate: 2.4 % / kh

Galvanostatic measurements

SOFC without PSC after 15 h test

SOFC with PSC after 100 h test

By the application of PSC, remarkably stable cell voltage was obtained even under the severe operating condition prone to carbon deposition.

5 µm

Agglomezated Ni Carbon fiberYSZ

Metal dust

18Stability of SOFCs with and without PSC

PSC serves as an anti-coking agent.10 µm

Microstructure of Ni-YSZ

19

Temperature homogenization in a planar reaction field using PSC technology

Suppression of temperature gradient using PSC techn ology

CathodeElectrolyte(YSZ)Inorganic fiber network Void ~20µm

Nano-sized metal catalyst

Ionic conductive fiber

SOFC

“Paper converting biogas to syngas”

PSC Install in a energy conversion device

Biogas

Final goalDevelopment of

internal reforming SOFC running on biofuels

Catalytic activity for reforming reactionLow High

⇒Temperature homogenization in a cell

Anode active layer (Ni-YSZ)

Array of PSCs with different catalytic activity

・ No carbon deposition・ Tolerant to deactivation by contaminants

・ Suppression of catalyst agglomeration・ Enhanced gas diffusivity

Electricity

Development of functionally-graded catalytic reacti on fieldSupported by Industrial Technology Research Grant Program in 201 1 from New Energy and Industrial Technology Development Organi zation (NEDO) of Japan

20

Monitoring of dry reforming methane to build a kine tic model 21

♦ Temperature decrease is easily adjustable by controlling Ni precursor concentration in the impregnation process of PSC.

Temperature change caused by the dry reforming of methane

0 200 400 600 800 1000-20

-15

-10

-5

0

5

0.02M Ni (0.15wt% Ni)

Temp: 800 oC

0.05M Ni (0.38wt% Ni)

0.1M Ni (0.76wt% Ni)

Time / s

Tem

pera

ture

dec

reas

e / o

C

T.C. was placed between the two papers.

Data logger

20 mm

♦ CH4 conv.♦ H2 production rate♦ CO production rate♦ Temp. decrease

T.C.

Fuel(simulated biogas)CH4 : CO2 = 1 : 1

Off-gas

800 or 750 oC

Paper-structured catalyst

to GC

Methane dry reforming test

CH4:CO2:N2(ml min-1) = 20:20:20

22Sensitivity analysis

Elementary reactions, Blaylock et al., J. Phys. Chem. C, 113 (2009) 4898

*: vacant site on the Ni surface.i*: adsorbed chemical species

According to the sensitivity analysis by changing activation energies in the base mechanism,

Recombination reactions of CH* with oxygenated adsorbants, Rx. 15 and 16, were found to be the most sensitive to the conversion and selectivity in dry reforming of methane.

Second sensitive reaction was CO2* decomposition, which is the reverse reaction of Rx. 35.

Reaction 15 : CH* + O* = CHO* + *, Ea = 101 kJ mol-1

Reaction 16 : CH* + OH* = CHOH* + *, Ea = 73 kJ mol-1

Reaction 35 : O* + CO* = CO2* + *, Ea = 124 kJ mol-1

23

H2 formation rate

0.01 0.1 1 100

10

20

30

40

50

60

70

80

0.01 0.1 1 100

10

20

30

40

50

60

70

80H

2pr

oduc

tion

rate

/ m

l min

-1

Ni concentration / M Ni concentration / M

H2

prod

uctio

n ra

te /

ml m

in-1

Temp: 800 oC

20:20:20

CH4:CO2:N2(ml min-1) = 40:40:40

20:20:20

40:40:40

20 : 20 : 20 ex.20 : 20 : 20 cal.40 : 40 : 40 ex.40 : 40 : 40 cal.

0.01 0.1 1 100

10

20

30

40

50

60

70

80

0.01 0.1 1 100

10

20

30

40

50

60

70

80

Ni concentration / M Ni concentration / M

CO

pro

duct

ion

rate

/ m

l min

-1

CO

pro

duct

ion

rate

/ m

l min

-120:20:20

40:40:40

40:40:40

20:20:20

Fuel: CH4/CO2 = 120 : 20 : 20 ex.20 : 20 : 20 cal.40 : 40 : 40 ex.40 : 40 : 40 cal.

20 : 20 : 20 ex.20 : 20 : 20 cal.40 : 40 : 40 ex.40 : 40 : 40 cal.

20 : 20 : 20 ex.20 : 20 : 20 cal.40 : 40 : 40 ex.40 : 40 : 40 cal.

Temp: 800 oCFuel: CH4/CO2 = 1

Temp: 750 oC

Fuel: CH4/CO2 = 1

Temp: 750 oC

Fuel: CH4/CO2 = 1

Reaction rate of dry reforming of methane

CO formation rate

24CH4 conversion vs temperature decrease

0.0 0.2 0.4 0.6 0.8 1.0-35

-30

-25

-20

-15

-10

-5

0

0.0 0.2 0.4 0.6 0.8 1.0-35

-30

-25

-20

-15

-10

-5

0

Tem

pera

ture

dec

reas

e / K

CH4 conversion / - CH4 conversion / -

20:20:20

40:40:40

20:20:20

40:40:40

Tem

pera

ture

dec

reas

e / K

Correlation between methane conversion and local te mperature decrease caused by the dry reforming of methane

♦ Calculated results were well accorded with experimental ones.♦ Kinetic simulation model build in this study can precisely predict local temperature decrease if a certain methane conversion is given.

Using the established model a functionally-graded reaction field leading to uniform temperature distribution in a planar reactor during biogas reforming can be designed.

20 : 20 : 20 ex.20 : 20 : 20 cal.40 : 40 : 40 ex.40 : 40 : 40 cal.

20 : 20 : 20 ex.20 : 20 : 20 cal.40 : 40 : 40 ex.40 : 40 : 40 cal.

Temp: 800 oCFuel: CH4/CO2 = 1

Temp: 750 oCFuel: CH4/CO2 = 1

Ni

YSZ plate

Ceramic bond

Simulated biogas（CH4/CO2 = 1)

Off-gasto gaschro

Inorganic fiber

PSC strip

Biogas

25

The array of PSC strips Measurement of temp. distribution

Before test

0.04M Ni0.5M Ni+1.0M Mg

0.1M Ni+0.5M Mg0.065M Ni

CH4/CO2= 1

♦Temperature homogenization ♦ Suppression of carbon deposition♦ Avoidance of destruction of the adjacent ceramic material♦ Stabilization of planar reformer

ThermographyParameter・ CH4/CO2 ratio・ Air/Biogas ratio・ Furnace temp.

Design of functionally-graded reaction field

Off-gas

Objective5 cm

5 cm

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0-100

-80

-60

-40

-20

0

20

Tem

pera

ture

dec

reas

e / o

C

Distance / cm

Fuel: Simulated biogas(CH4/CO2 = 1), 180ml min-1

Furnace temp: 800 oC

in out

Exp. I, One PSC(uniform catalyst )

Exp. II, PSC array(functionally graded)

Temperature homogenization

Exp. II

Calculation

Exp. I

Calculation

in out in out

26

Line distribution

♦ Temp. gradient caused by the dry reforming of methane was reduced down to 1/4 by the application of PSC array at the same CH4 conversion.♦ Sever coking occurred in the Exp. I caused by the strong temperature decrease by 90 oC, which can thermodynamically induce carbon formation.

Temperature distribution during dry reforming of me thane

0.5M Ni/ZfCfZs(3.8 wt% Ni)

0.04

M N

i

0.5M

Ni+

1.0M

Mg

0.1M

Ni+

0.5M

Mg

0.06

5M N

iCH4 conv. = 91 % CH4 conv. = 91 %

after 100 h

PSC

After test (35 h)

Coking

4 different PSCs

in out in out

4 cm

4 cm

No coking

27

♦ Inorganic fiber network including YSZ fiber which acts as catalyst support was created by the simple paper-making process.

♦ Novel Ni-loaded paper-structured catalysts (PSCs) with excellent catalytic activity for the reforming of biofuels were designed and developed.

♦ The significant advantages of the PSCs are their high mechanical flexibility and material workability to be easily applied to SOFC.

♦ So far, a functionally-graded reaction field which leads to uniform temperature distribution during biofuel reforming resulting in stable operation of planar reactor such as SOFC was successfully developed.

Summary

Acknowledgements 28

This study was supported by Industrial Technology Research Grant Program in 2011 from New Energy and Industrial Technology Development Organization (NEDO) of Japan.