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Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Performance Studies of Copper-Iron/Ceria-Yttria Stabilized Zirconia
Anode for Electro-oxidation of Hydrogen and Methane Fuels in
Solid Oxide Fuel CellsPresented by Gurpreet Kaur
Department of Chemical EngineeringIndian Institute of Technology Delhi
International Conference on Advances in Energy ResearchDecember 10-11, 2013
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Solid Oxide Fuel CellSolid oxide fuel cell is a device that converts gaseous fuels (hydrogen, natural gas) via an electro-chemical process directly into electricity. Salient Features of SOFC
SOFCs are over 60 % efficient (conversion of fuel to
electricity)
Provides environment friendly power generation
Principle of SOFC
22 2
24 2 2
24 10 2 2
2 2 2 4
4 2 8
13 4 5 26
H O H O e
CH O CO H O e
C H O CO H O e
22
22
22
4 2
8 4
26 13
O e O
O e O
O e O
Anode Side Reactions
Cathode Side Reactions
Operating Temperature: 700-1000 °C
Conventional SOFC ComponentsElectrolyte – 8 % Yttria Stabilized
Zirconia (YSZ) – a pure ionic conductorAnode – Ni provides electronic conductivity and enables electrochemical oxidation of fuel.Cathode - La0.8Sr0.2MnO3 (LSM) provides electronic conductivity and enables electrochemical reduction of O2.
1
ApplicationsStationary electrical power generation
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Why Direct Hydrocarbons ?
Anode requirements for oxidation of hydrocarbons
High electro catalytic activity for oxidation of fuel Good electronic conductivity for transport of electrons from
the TPB Good ionic conductivity for transport of oxide ions to the
TPB Sufficient porosity for diffusion of fuel gases and exhaust
gases to and from the TPB
Production of hydrogen by steam reforming reactions of natural gas and higher hydrocarbons requires additional purification steps to satisfy fuel cell demands
Direct hydrocarbon solid oxide fuel cell can operate in hydrocarbon fuels without the need for pre-reforming.
2
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Anodes for Direct Hydrocarbon Solid Oxide Fuel Cell Nickel/Yttria-stabilized Zirconia based Anodes1
High catalytic activity for fuel oxidation and for steam reforming of methane
Relatively inexpensive; chemically and physically compatible with YSZ electrolyte
Problems in use with dry hydrocarbons; Tends to promote carbon deposition1
1. M .L.Toebes, J.H. Bitter, A.J. Van Dillen and K.P.de Jong, Catal. Today 2000; 76, 33 – 42 .
2. R. J. Gorte, S. Park, J. M. Vohs, C. Wang, Adv Mater. 2000; 12: 1465 -69
Copper/Ceria/Yttria Stabilized Zirconia2- Alternative anode material for direct hydrocarbons
CeO2 : Mixed ionic and electronic conductor in reducing medium.
Good oxidation catalyst for hydrocarbons Poorer electronic conductor Cu: To increase the electronic conductivity, addition of Cu is necessary Cu/CeO2-YSZ anodes are stable in variety of hydrocarbons
Limited by lower performance (~ 100 mW/cm2 at 800 °C).
Literature Review
3
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Objective of Research Work Fabrication of complete solid oxide fuel cell in laboratory scale using tape casting
technique of thickness of < 600 µm and anode porosity of 70 %. Additives composition is optimized to get defect free SOFC
Preparation of Cu/CeO2-YSZ and Cu-Fe/CeO2-YSZ anodes using wet impregnation method.
Characterization of prepared anodes using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental dispersive X-ray (EDX) to investigate the thermal, structural, morphological properties and elemental analysis
Current-Voltage characterization of prepared anodes with YSZ electrolyte and LSM-YSZ cathodes in H2 and methane fuels.
Frequency response analysis of SOFC with prepared anodes to study various resistances e.g. ohmic resistance, polarization resistance.
Study the effect of temperature, bimetallic molar ratio and addition of precious metals on the performance of SOFC in H2 and methane fuels.
Investigation of carbon deposition using optical microscopy and thermal gravimetric analysis.
Longevity testing in methane fuel.
4
Gurpreet Kaur and Suddhasatwa Basu, Journal of Power Sources, 241, 783-790, 2013
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Magnetic Stirring, 24 h
Binder (Polyethylene Glycol and Polyvinyl
butryl)
Electrolyte Tape Casting and Drying for 24 h
Solvent (Ethanol and MEK)+
Dispersant (oleic acid)
Stirring
Homogeneous SlurryStirring
Magnetic Stirring, 24 h
Homogeneous Slurry
Yttria-Stabilized ZirconiaPore-formers i.e. Graphite and Polystyrene) for anode only
Porous YSZ Anode Tape Casting and Drying for 24 h
Co-sintering, 1450 °C
Tape casted electrolyte layer
Porous YSZ layer on dense YSZ
electrolyte
SEM of porous YSZ
Porosity 70 vol %
SEM of porous and dense YSZ sintered at
1450 ºC
Preparation Procedure for Anode and Electrolyte Slurry for Tape Casting
SOFC Fabrication
Component Quantity
YSZ 24 gmGraphite 5 gmPolystyrene 3.8 gmEthanol (EtOH)
16 mlMethylethyl ketone (MEK) 9 mlOleic acid
1.0 mlPolyvinyl butyral (PVB) 3.8 gmPolyethylene glycol (PEG)
3 ml
Composition of anode and electrolyte for tape casting slurry
No poreformers (graphite and polystrene) added in electrolyte slurryFabrication issues
Green tape – Pin holesSintered layers – cracking, delamination etc 5
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Preparation Procedure of Anode for SOFC
TGA of impregnated nitrate solution in porous YSZ
Data was collected from room temperature to 1000 BC at a rate of
10 BC/min. Zero air flow rate: 50 ml/min Calcination temperature of 400 ºC is selected to get metal oxides
(Wet Impregnation Method)Porous YSZ
Repeated impregnation to get desired loading
Calcinations at 400 ºC for 2 h
Impregnation of 1M Ce(NO3)3, 6H2O
Calcinations at 400 ºC for 2 h
Anode Cu/CeO2-YSZ and Cu-Fe/CeO2-YSZ
Impregnation of 1M Cu(NO3), 3H2O and Fe(NO3)3, 9H2O solution
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Cu-Fe [1:1]
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Synthesis Procedure of Cathode (La0.8Sr0.2MnO3)
Dissolve La(NO3)3, Sr(NO3)2, Mn(NO3)2 in stoichiometric ratio
Calcination1100 oC for 2 h
Mixing (Agate mortar)La0.8Sr0.2MnO3– 0.45 g
YSZ – 0.45 gGraphite– 0.1 g
Slurry preparationMixed powders with
glycerol
0
500
1000
1500
2000
2500
20 30 40 50 60 70 80
Inte
nsi
ty (
cps)
2θ( � )
XRD spectra of La0.8Sr0.2MnO3
All peaks corresponds to perovskite phase
Particles size of LSM ~0.3 µm
SEM of La0.8Sr0.2MnO3
La0.8Sr0.2MnO3 showed good chemical and thermal compatibility with YSZ electrolyte material
* R.J. Bell, G.J. Millar, J. Drennan, Solid State Ionics 2000; 131: 211–220.
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Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Experimental set up and Procedure
CathodeLSM:YS
Z
Electrolyte
YSZ
High Temperature SOFC Furnace
PGSTAT 30, Autolab (i-V and impedance measurements)
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Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
X-ray Diffraction of Cu-Fe/CeO2-YSZ Anodes
Cu-Fe/CeO2-YSZ anodes were prepared for three molar ratios of Cu-Fe [1:0, 3:1 and 1:1].
Peaks at 43.3º and 44.2° corresponds to Cu and Fe and in metals are present cubic structure.
Small shift in the peaks for Cu and Fe was observed in the spectra, according to phase diagram1, some Fe can be incorporated in Cu phase at 800 °C.
1. Turchanin MA, Agraval PG, Nikolaenko IV, J Phase Equilibria 2003;24:307-19.
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++*,o
¤
*
•
••
•
•
(a)
(b)
(c)
¤
ɵ
ɵ
0
2000
4000
6000
8000
25 35 45 55 65 75
Inte
nsit
y (a
.u)
2 Theta (Degree)
Ɣ
(a)
(b)
(c)
(d)
Ɣ Ɣ Ɣ
ƔƔ
** *
Ÿ
Ƈ
Ƈ
ο ¤¤ ¤ ¤
ο
(•) YSZ(*) Fe2O3
(o) CuFe2O4
(+) CuO(¤) Cu(ɵ) Fe
XRD patterns of (a) YSZ, (b) Cu-Fe/YSZ calcined at 300 °C (c) Cu-Fe/YSZ reduced at 800 °C
XRD patterns of (a) YSZ, (b) Fe/CeO2-YSZ, (c) Cu/CeO2-YSZ and (d) Cu-Fe/CeO2-YSZ after reduction in H2 at 800 °C
(●) YSZ (▲) Cu (♦) Fe (*) CeO2 (ο) Fe3O4 (¤) Fe2O3
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Addition of Fe in Cu based anodes improves the
catalyst dispersion Better interconnection between
particles helps to improve the electrical conduction and provides more surface area for fuel oxidation reaction Particle size was observed to be 1 µm
20 wt% Cu-Fe [3:1]
Scanning electron microscopy of Cu-Fe/CeO2-YSZ anodes after reduction in H2 at 800ºC
20 wt% Cu-Fe [1:1]
20 wt% Cu-Fe [3:1]
10 wt% CeO2, 20 wt% Cu-Fe [1:0, 3:1 and 1:1]
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Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Elemental dispersive analysis of Cu/CeO2-YSZ and Cu-Fe/CeO2-YSZ anodes
Presence of metals inside the pores with no significant impurity observed.
Results indicate the success of fabrication of anodes by wet impregnation method.
11
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
SEM of SOFC shows anode, electrolyte and cathode thickness of 90, 80 and 40 µm.
Power density of ~ 190, 260 and 330 mW/cm-2 was observed for Cu-Fe/CeO2-YSZ anodes for Cu-Fe molar ratio of 1:0, 3:1 and 1:1.
Performance increased with increase in Fe loading in Cu/CeO2-YSZ anodes
Performance of SOFC in H2 at 800°C (Cu-Fe/CeO2/YSZ anodes for Cu-Fe molar ratio of 1:0, 3:1 and 1:1, YSZ as electrolyte,
LSM/YSZ as cathode
~90 µm
80 µm
40 µm
SEM of SOFC Performance Curves
i-V (filled symbols) and power curves (open symbols) for different molar ratio of Cu-Fe
0
50
100
150
200
250
300
350
400
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800
Pow
er D
ensi
ty (m
W/c
m2 )
Vol
tage
(V)
Current Density (mA/cm2)
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Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
0
0.1
0.2
0.3
0 0.3 0.6 0.9 1.2 1.5 1.8
-Zim
(ohm
cm
2 )
Zre (ohm cm2)
0
0.1
0.2
0.3
7 7.5 8 8.5 9 9.5 10
-Zim
(ohm
cm
2)
Zre (ohm cm2)
Calculated electrolyte resistance for 80 µm thick electrolyte is ~0.38 Ω. cm2. Less additional ohmic resistance was observed for Cu-Fe [1:1] due to better dispersion
between catalyst particles resulting better electronic conduction.Total polarization resistance decreases with increase in Fe molar ratio suggest that
prepared anodes have better electro-catalytic activity towards oxidation of H2.
Improvement in the performance of cell might also be due to incorporation of Cu and Fe ions in CeO2 lattice
Lattice parameter CeO2 calculated from XRD: 5.36Å Pure CeO2 lattice parameter- 5.41 Å
EIS of SOFC for different molar ratio of Cu-Fe of 1:0(∆), 3:1 (◊)
and 1:1 (□)
XRD of Cu-Fe/CeO2-YSZ anode after reduction in H2
13
RΩ
Rp
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Optical microscopy images of Cu-Fe/CeO2-YSZ anodes for Cu-Fe molar ratio of (a) 1:0, (b) 3:1 (c) 1:1 after exposure to CH4 for 1h
(a) (b) (c)
Metal wt% in porous
CeO2/YSZ
Weight
change (%)
Cu: Fe [1:0]- (20wt%)
-0.030
Cu: Fe [3:1]- (20wt%)
-0.027
Cu: Fe [1:1]- (20wt%)
-0.021
Table - Weight changes after CH4 flow
TGA of Cu-Fe/CeO2-YSZ anode after reduction in (a) H2 and (b) H2 followed by exposure of CH4 for 1 h
No significant weight gain was observed due to carbon deposition after CH4 flow
Characterization of Cu-Fe/CeO2-YSZ anodes after exposure to CH4
at 800°C
14
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
0
50
100
150
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250 300 350
Pow
er D
ensi
ty (m
W/c
m2 )
Vol
tage
(V)
Current Density (mA/cm2)
Cu-Fe [1:1] Cu-Fe [3:1] Cu-Fe [1:0]
Performance of Cu-Fe/CeO2-YSZ anodes in CH4 at 800 ºC
Cu-Fe/CeO2/YSZ anodes for Cu-Fe molar ratio of 1:1 showed higher performance than 1:0 and 3:1.
Performance of all the anodes are lower in CH4 than H2 might be due to less reactive nature of CH4
in comparison to H2. OCV was observed to be less than Nernst potential (> 1.05 V ) suggesting that
complete oxidation of CH4 is not taking place. Oxidation of hydrocarbon on surface may occur in multiple steps and
equilibrium has been established between hydrocarbons and partial oxidation products.
15
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Effect of addition of 1 wt% Pd on the performance of Cu-Fe/CeO2-YSZ anodes in H2 and CH4
Significant improvement in the cell performance in CH4 was observed with addition of 1 wt% of Pd
Results suggest that resistance associated with surface reactions decreases with addition of 1 wt% Pd.Anode 160 µm, Electrolyte 100 µm
Performance curves of Cu-Fe/CeO2-YSZ anodes with (□) and without (○) 1 wt% Pd
16
0
50
100
150
200
250
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400 500 600
Pow
er D
ensi
ty (m
W/c
m2 )
Vol
tage
(V)
Current Density (mA/cm2)
Cu-Fe [1:1]
H2
0
20
40
60
80
100
120
140
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400
Pow
er D
ensi
ty (m
W/c
m2 )
Vol
tage
(V)
Current Density (mA/cm2)
Cu-Fe [1:1]
CH4
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
0
0.1
0.2
0.3
0.4
0 0.5 1 1.5 2
-Zim
(ohm
cm
2 )
Zre (ohm cm2)
22 h
30 h
46 h0
0.05
0.1
0.15
0.2
0.3 0.4 0.5 0.6
-Zim
(ohm
cm
2 )
Zre (ohm cm2)
1 h
Long term performance of Cu-Fe/CeO2/YSZ anodes in CH4
Power density decreased from 125 mW/cm2 to 100 mW/cm2 during 46 h testing
Increase in ohmic resistance may be due to increase in particle size of catalyst particles at
800 °C during stability test. (repeated thrice). Increase in ohmic resistance and polarization resistance might be
responsible for this loss. Cu-Fe/CeO2/YSZ anode showed much better stability than Ni/YSZ
anodes in which complete performance degradation takes place within 5 h.
0
50
100
150
200
0 10 20 30 40 50
Pow
er D
ensi
ty (m
W/c
m2 )
Time (h)
Cu-Fe [1:1]
CH4, 800 °C
0.5V
17
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
SEM and TGA of Cu-Fe/CeO2-YSZ anodes after cell testing in
CH4 for 46 h
SEM shows catalyst particle size increased from 1.0 to 1.5 µm after cell operation at 800 °C for 46 h
TGA shows no significant weight loss suggesting that carbon ,if present, is not in significant quantity.
18
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Summary
SOFC Fabrication and Electrochemical Characterization Solid oxide fuel cells was fabricated by tape casting and wet impregnation
method. Additives (pore-formers, binder and solvent) composition was optimized to
get defect free button cells.SOFC testing (i-V and EIS) was carried out for Cu/CeO2-YSZ and Cu-Fe/CeO2-
YSZ anodes with YSZ as electrolyte and LSM/YSZ as cathode.
Performance of Cu-Fe/CeO2-YSZ Anodes in H2 and Methane XRD shows the formation of Cu and Fe phase. Addition of Cu to Fe enhances
the reduction of Fe. SEM shows that better dispersion between catalyst particles achieved with
addition of Fe in Cu/CeO2-YSZ anodes Addition of Fe in Cu/CeO2-YSZ anodes showed improved performance in H2
and CH4 fuels. Electrochemical impedance spectra showed less ohmic as well as charge
transfer resistance for Cu-Fe/CeO2-YSZ anodes in comparison to Cu/CeO2-YSZ anodes.
SOFC performance increased with addition of 1 wt % Pd in Cu-Fe/CeO2-YSZ anodes.
No significant degradation in the performance observed during cell operation in CH4 suggesting that anodes are stable in comparison to conventional Ni/YSZ anodes.
19
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
References
20
[1] Lashtabeg, A. and Skinner, S. J. (2006) Solid oxide fuel cells-a challenge for materials chemists, Journal of materials chemistry, 16, pp. 3161-70.[2] Baker, R. T. K. (1989) Catalytic growth of carbon filaments, Carbon, 27, pp.1315-23.[3] Gorte, R. J., Vohs, J. M. (2003) Novel SOFC anodes for direct electrochemical oxidation of hydrocarbons, Journal of catalysis, 216, pp. 477-86.[4] Gorte, R. J., Park, S., Vohs, J. M. and Wang, C. (2000) Anodes for direct oxidation of dry hydrocarbons in solid oxide fuel cells, Advanced Material, 12, pp.1465-69.[5] Zhu, H., Wang, W., Ran, R., Su, C., Shi, H. and Shao, Z. (2012) Iron incorporated Ni-ZrO2 catalysts for electric power generation from methane, International Journal of Hydrogen Energy, 37, pp. 9801-9808.[6] Gordes, P., Christiansen, N., Jensen, E. J. and Villadsen, J. (1995) Synthesis of perovskite-type compounds by drip Pyrolysis, Journal of Material Science, 30, pp.1053-58.[7] Mitterdorfer, A. and Gauckler, L.G. (1998) La2Zr2O7 formation and oxygen reduction kinetics of La0.85Sr0.15MnYO3,O2(g) YSZ system, Solid State Ionics, 111, pp. 185-218.[8] Turchanin, M. A., Agraval, P. G. and Nikolaenko I. V. (2003) Thermodynamics of alloys and phase equilibria in the copper iron system, Journal of Phase Equilibria, 24, pp. 307-309.[9] Kameoka, S., Tanabe, T. and Tsai, A. P. (2005) Spinel CuFe2O4: a precursor for copper catalyst with high thermal stability and activity, Catalysis Letters, 100, pp. 89-93. [10] Lv, H., Tu, H., Zhao, B., Wu, Y. and Hu, K. (2007) Synthesis and electrochemical behavior of Ce1-xFex02-δ as a possible SOFC anode materials, Solid State Ionics, 177, pp. 3467-3472.[11] Xing, Z., Hua, W., Honggang, W., Kongzhai, L. and Xianming C. (2010) Hydrogen and syngas production from two-step steam reforming of methane over CeO2-Fe2O3 oxygen carrier, Journal of Rare Earth, 28, pp. 907-913.[12] Buccheri, M. A., Singh, A. and Hill, J. M. (2011) Anode- versus electrolyte-supported Ni-YSZ/YSZ/Pt SOFCs: Effect of cell design on OCV, performance and carbon formation for the direct utilization of dry methane, Journal of Power Sources, 196, pp. 968-976
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Thank You
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Department of Chemical Engineering Indian Institute of Technology-Delhi, New Delhi 110 016, India
Nernst Potential calculation for multiple reactions
4 2 2 2
4 2 2
2 2
2
2 2
4 2 2
2 2
3 / 2 2
1/ 2
1/ 2
2
CH O CO H O
CH O CO H O
C O CO
C O CO
CO O CO
CH O C H O
Experimental
/E G nF
An observed OCV is less than Nernst potential suggesting that complete oxidation of methane is not taking place.
Multiple anode reactions may occur simultaneously with dominating contribution from one reaction.
0.85
0.9
0.95
1
1.05
1.1
1.15
850 900 950 1000 1050 1100
OC
V (V
)
Temperature (� K)