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Oxygen chemical potential profile in a solid oxide fuel cell and simulation of electrochemical performance
Solid State Ionics 40/4 1 ( 1990) 4 15-420 North-Holland
OXYGEN CHEMICAL POTENTIAL PROFILE AND SIMULATION OF ELECTROCHEMICAL
IN A SOLID OXIDE FUEL CELL PERFORMANCE
Akihiro SAWATA, Kikuji TSUNEYOSHI Mitsubishi Heavy Industries, Ltd., 1-8-1 Sachiura, Kanazawa-ku, Yokohama 236, Japan
Junichiro
MIZUSAIU
and Hiroaki TAGAWA
Institute of Environmental Science and Technology, Yokohama National University, 156 Tokiwadai, Hodogaya-ku. Yokohama 240, Japan
Based on the reported kinetic equations on the air and fuel electrodes, simulation was made on the oxygen potential profile in a solid oxide fuel cell (SOFC) and the electrochemical performance. As a model for simulation, we considered the SOFC of the type, H,-H,O/porous Pt electrode/YSZ/porous La&&.4MnOJOz(g). In the previous papers, we reported the empirical rate equations calculated from the results of the complex impedance due to electrode reaction and the steady-state polarization for the Oz(g)/porous La,&&,MnOJYSZ electrode and for the Hz-H,O/porous Pt/YSZ electrode. They were expressed using oxygen activity, ao, in YSZ at the electrode/YSZ interface and the partial pressures of gaseous components: I=b(&-aG’Po2 ) for the ‘I2 for the fuel electrode, where I is the steady-state current density, air electrode, and I=kH(PH,P# K&-P~jf2PHS(Ka0)b and kH are the rate constants and K is the equilibrium constant of Hz-H20-O2 system. Here, b and kH were related to the electrode interface conductivities u,(O) and Us by ~~(0) =4F!@&/‘/RT and u,(H)=3Fk,P&/RT. Using the above equations and the relationship of ho= (RT/2) In PoZ, the & profiles in SOFC were calculated with current density and the interface conductivities as parameters. Also, I-Vcurves of SOFC were simulated with the electrolyte thickness as the additional parameter to predict the performance of SOFC with any cell construction.
1. Introduction
electrochemical previously.
Recently, with the revelation of serious environmental problems of global scale caused by the fossil fuel consumption, it becomes urgent to develop highly efficient system for fossil energy conversion. Because solid oxide fuel cells (SOFC) are considered as one of the desirable system, many groups have been involved for the development of SOFC and the research become further more active. So far, our group have focused our interest on the fundamentals of the electrode reaction of SOFC [ l-4 1. In the previous papers, we showed the relationship between the reaction process and the morphology [ 1,2 1, and determined the empirical rate equations for the air and fuel electrodes [ 3,4]. In this work, we reveal the calculation procedures for the oxygen chemical potential profiles and the electrochemical performance in SOFC using the 0167-2738/90/$03.50 (North-Holland )
0 Elsevier Science Publishers
B.V.
data
and rate equations
reported
2. Basic concept for the electrode reaction and the rate equations 2.1. Nature of electrode overpotential As described in the previous paper [ 5 1, the charge transfer reaction at the electrode/electrolyte interface cannot be the rate determining step of the electrode reaction at the three phase region of the reactant gas/porous electrode/solid electrolyte. Applying the reported model [ 5 1, the overpotential, q, is related to oxygen activity, aO, in YSZ at the electrode/ YSZ interface and the oxygen partial pressure, PO,, in the gas phase by the equation
416
q=RT/2Fln
A. Sawata et al. /Oxygen potential projile in SOFC
(ao/P&{2),
where a, in the oxide in equilibrium with gas is taken as unity. Using eqn. ( 1), the ships between steady-state current density, can be substituted for those between Z and
(1) 1 atm O2 relationZ, and r~ a,.
2.2.3. Rate equation for the fuel electrode For the case of H,-H20, Pt/YSZ system, the apparent reaction orders for PH2, m and n, seem to change with PH2 [4]. By the mathematical analysis of the polarization curves obtained for PH2> 10m2 atm, m, n, r, s, p and q of eq. (4’ ) were determined as 141
2.2. Rate equations
I=kH(PH~P~~~2Ka,-PH,oP&‘~2(Kao)-’~2},
2.2.1. General expressions for the rate equations at the SOFC electrodes When the rate determining step of the electrode reaction is not the charge transfer reaction, the reaction rate between gas phase and solid electrolyte can be described by the activity of the chemical species in the reaction process [ 61. Therefore, the current at the air and fuel electrodes can be expressed by the generalized equations I=k,{PG,“ag-P&,a,q}, for the air electrode,
(2) and
I=kH(P;;2PHPOab-PH:P;FIZOao”~
(2’)
for the fuel electrode, where ko and kH are the rate constants, PH2 and PHzo are the partial pressures of hydrogen and water vapor in Hz-H20 gas mixtures and m, n, p, q, r and s are the orders of the reaction for respective components. Because eqs. (2) or (2’ ) represent only one-reaction process, the order of forward reaction must be the same as the order of the backward reaction. Then, we have 2(m+n)=p+q for the air electrode m+n=r+s=p+q
(3) and (3’)
for the fuel electrode. 2.2.2. Rate equation for the air electrode By the mathematical analysis using eqns. ( 1) and (2), the orders of m, n, p and q were determined from the PO, dependence of steady-state polarization current on the air electrodes of O2 (g) /La0.&+,Mn03/ YSZ [ 31. The empirical rate equation was determined as (4)
where K is the equilibrium system [ 7 1. K=P,,ol
constant
(5)
of Hz-H20-O2
CPb’z*f’d
(6)
2.3. Electrode interface conductivity 2.3.1. Definition of the electrode interface conductivity In many studies, complex impedance techniques are employed for the measurements of electrode properties. From the impedance arcs obtained by the complex impedance measurement, we can determine the electrode interface resistance, RE, due to the overpotential at the electrode/electrolyte interface. The electrode interface conductivity, I&, is defined by the equation aE=l/ARE,
(7)
where A is area of the electrode/YSZ also given by 0,
=
(az/@),,,
interface.
.
GE is
(8)
2.3.2. Determination of k, and kH from 0~(0), a,(H) As shown by eq. ( 1 ), when q= 0, the equilibrium holds between a0 in YSZ interface and PO, in the gas phase. Then we have a0- -P&/2
.
(9)
Applying eqs. ( 1 ), (4) and ( 5) to eq. (8 ) and using eqs. (6) and (9), we obtain the relationships between the interface conductivity and the rate constant: (10) (11)
A. Sawataet al. /Oxygen potentialprofilein SOFC
Both eqs. ( 10) and ( 11) are consistent with the results of impedance measurements [ 3,4]. Thus, when oE( 0) and c+(H) are given from measurements of the interface impedance, we can calculate k. and kH by eqs. (10) and (11).
417 -interface
E
YSZ
45 Q
0
0
N
t
+
3. Oxygen chemical potential
2 V n_
profiles in SOFC
a&W=
!$gLL ‘01
/I
lOS/cnl2
10.
50
.
In discharging state of SOFC, the whole electrochemical reaction, proceeding across the electrode/ electrolyte interfaces and the electrolyte, takes place with the gradient of oxygen chemical potential, h, as the driving force. With eqs. (4) and (5), we can calculate the changes in ,uo at the electrode/YSZ interfaces as a function of current density. The relative oxygen chemical potential, Ah, is given by (ao/P;\‘2),
A,uo=po-&=RTln
r
> ":
100
0
5
150
2 z c" 200
:20z s x30? 40-
250 50-
(12)
where ,u& is h of the oxygen partial pressure in the reference gas, P&. Substituting Ab for a, of eqs. (4) and (5) with the help of eq. ( 12), the relation between I and Ah is expressed as,
Fig. 1. b profiles with various ~~(0) in the air electrode/YSZ interface under the current of I=200 mA/cm’ at 1000°C.
+terface
-exp(
-ACLo(O)IRT)}
(13)
for eq. (4), and
-exp[-&dH)I2RTlI
(14)
for eq. (5), where A&(O) and Ah(H) are the relative & to P& ( = 0.2 1 atm) in air and to P& in the H2-H20 gas mixtures, respectively. For given aE( 0) and GE(H ), k,, and kH can be determined from eqs. (10) and (11). Then,using eqs. (13) and (14), A&( 0) and A& (H ) can be calculated for any steady-state current. Figs. 1 and 2 show the h(O) and b(H) profiles, respectively, at the electrode/YSZ interface as a
bthode
tained by %athode
=bo(o)/2F
,0.5
1
5 10
and r,~,,,~~in figs. 1 and 2 were obFig. 2. h profiles with various a,(H) in the fuel electrode/YSZ interface under the current of I= 200 mA/cm* at 1000°C. Ratio of the fuel gas composition: HZO/H2 = l/9.
A. Sawata et al. /Oxygen
418
fuel
potential profile in SOFC
air electrode
electrode
Fig. 3. Steady-state oxygen chemical potential profiles in SOFC under the different current density (mA/cm2): (-) 0 (open circuit, approximation), (- - -) 50, (*-a-) 150, (*-*e-) 250 at 1000°C. The interface conductivities of fuel and air electrode: +(H) =O.l S/cm*, c+(O) = 1 S/cmZ.
and rlanode=Mo(H)I2F.
(15)
In figs. 1 and 2, log PO, is also indicated, which shows the effective PO, corresponding to the h in the cell. As shown in figs. 1 or 2, when a,< 1 S/cm’, the effective PO, at the interface is different by two or three orders of magnitude from the PO, of outer gas phase. Fig. 3 shows overall steady-state oxygen potential profiles in a SOFC as a function of current density at 1000°C for r&(O)= 1 S cm-* and o,(H)=O.l S cm-*. For simplicity, in this paper, we employ the approximation that the k profiles in YSZ are linear, as shown in fig. 3. Because the ionic transport number in YSZ is close to unity and the electronic conductivity is very small for 1O-)O
tiles in fig. 3 holds under the conditions with the steady-state current density of the order of mA and the more [9]. However, for the open circuit condition and under very small current of, maybe, less than 1 mA/cm*, the fi profiles deviates from the linear relationships. In this paper, we do not mention the further details of the chemical potential profiles in the YSZ layer because the precise calculation procedures for the ~0 profiles in the bulk YSZ were already given by Choudhury and Patterson [ 91.
4. Simulation of electrochemical characteristics Using the difference of h in YSZ between the two electrode interfaces, Ah (YSZ), the output voltage, E, of SOFC under steady-state current, I, is given by
419
A. Sawata et al. /Oxygen potential profile in SOFC
____-_:
100
- -.---___:
200
__--_--___: 500 lOOO”C,
0.6
air;Po2=0.2latm a02-‘0.
lScm-1
L 50
I
I
I
0
100
1
l50 i/
-2
200
I
250
300
mAcm
r
0 a I
-
1000°C.
100
Fig. 4. Simulated
___---: 200 __________-: 500 air: Po2=0.2latm. cIo2_=0.1Scm -I
fuel;
,PH20/P,2’1/9
: o.7w
1
I-V relationships
E= A~(YSZ)/2F-iL/ao~-
7
-.__
of a SOFC for different
,
electrolyte
(19)
where L is the thickness and ao2_ is the oxide ion conductivity of YSZ. Ah(YSZ) under steady-state is calculated by subtracting Ab( 0) and Ah(H) from Ah(YSZ) of the open circuit condition. Fig. 4 shows the steady-state I-Ah and I-E curves of SOFC at 1000°C with a,(O), r+(H) and L as pa-
thickness.
rameters. Here, the composition of H,O/H, gas mixtures was taken as l/9 and uoz- was fixed as 0.1 S/ cm. With the simulation described in this paper, when aE (0 ), oE( H) and ao2- are given, we can determine the limit of electrolyte thickness for the SOFC of desired Z-V characteristics. This simulation would be useful for the designing of SOFC cell construction.
420
A. Sawata et al. /Oxygen
[ I] J. Mizusaki, H. Tagawa, K. Tsuneyoshi, K. Mori and A. Sawata, Nippon Kagaku Kaishi (1988) 1623. [2] J. Mizusaki, H. Tagawa, K. Tsuneyoshi and A. Sawata, in: Proc. 1st Intern. Symp. SOFC, ed. S.C. Singhal, Vol. 89-l 1 (The Electrochem. Sot., NJ, 1989) pp. 254-264. [3] K. Tsuneyoshi, K. Mori, A. Sawata, J. Mizusaki and H. Tagawa, Solid State Ionics 35 (1989) 263. [ 41 J. Mizusaki, H. Tagawa, I. Koshiro, K. Isobe, K. Hirano and K. Fueki, presented at the 56th meeting of ECS Japan ( 1989) lG32, to be published.
potential
profile in SOFC
[ 5 ] J. Mizusaki, K. Amano, S. Yamauchi and K Fueki, Solid State Ionics22 (1981) 313. [6] H. Kobayashiand C. Wagner, J. Chem. Phys. 26 (1957) 1609. [7] M.W. Chase, Jr., C.A. Davies, J.R. Downey, Jr., D.J. Frurip, R.A. McDonald and A.N. Syverud, JANAF Thermochemical Tables, 3rd Ed., J. Phys. Chem. Ref. Data 14, Suppl. 1 ( 1985). [ 81 W. Weppner, J. Solid State Chem. 20 ( 1977) 305. [ 9 ] N.S. Choudbury and J.W. Patterson, J. Electrochem. Sot. 118 (1971) 1398.
OXYGEN CHEMICAL POTENTIAL PROFILE AND SIMULATION OF ELECTROCHEMICAL
IN A SOLID OXIDE FUEL CELL PERFORMANCE
Akihiro SAWATA, Kikuji TSUNEYOSHI Mitsubishi Heavy Industries, Ltd., 1-8-1 Sachiura, Kanazawa-ku, Yokohama 236, Japan
Junichiro
MIZUSAIU
and Hiroaki TAGAWA
Institute of Environmental Science and Technology, Yokohama National University, 156 Tokiwadai, Hodogaya-ku. Yokohama 240, Japan
Based on the reported kinetic equations on the air and fuel electrodes, simulation was made on the oxygen potential profile in a solid oxide fuel cell (SOFC) and the electrochemical performance. As a model for simulation, we considered the SOFC of the type, H,-H,O/porous Pt electrode/YSZ/porous La&&.4MnOJOz(g). In the previous papers, we reported the empirical rate equations calculated from the results of the complex impedance due to electrode reaction and the steady-state polarization for the Oz(g)/porous La,&&,MnOJYSZ electrode and for the Hz-H,O/porous Pt/YSZ electrode. They were expressed using oxygen activity, ao, in YSZ at the electrode/YSZ interface and the partial pressures of gaseous components: I=b(&-aG’Po2 ) for the ‘I2 for the fuel electrode, where I is the steady-state current density, air electrode, and I=kH(PH,P# K&-P~jf2PHS(Ka0)b and kH are the rate constants and K is the equilibrium constant of Hz-H20-O2 system. Here, b and kH were related to the electrode interface conductivities u,(O) and Us by ~~(0) =4F!@&/‘/RT and u,(H)=3Fk,P&/RT. Using the above equations and the relationship of ho= (RT/2) In PoZ, the & profiles in SOFC were calculated with current density and the interface conductivities as parameters. Also, I-Vcurves of SOFC were simulated with the electrolyte thickness as the additional parameter to predict the performance of SOFC with any cell construction.
1. Introduction
electrochemical previously.
Recently, with the revelation of serious environmental problems of global scale caused by the fossil fuel consumption, it becomes urgent to develop highly efficient system for fossil energy conversion. Because solid oxide fuel cells (SOFC) are considered as one of the desirable system, many groups have been involved for the development of SOFC and the research become further more active. So far, our group have focused our interest on the fundamentals of the electrode reaction of SOFC [ l-4 1. In the previous papers, we showed the relationship between the reaction process and the morphology [ 1,2 1, and determined the empirical rate equations for the air and fuel electrodes [ 3,4]. In this work, we reveal the calculation procedures for the oxygen chemical potential profiles and the electrochemical performance in SOFC using the 0167-2738/90/$03.50 (North-Holland )
0 Elsevier Science Publishers
B.V.
data
and rate equations
reported
2. Basic concept for the electrode reaction and the rate equations 2.1. Nature of electrode overpotential As described in the previous paper [ 5 1, the charge transfer reaction at the electrode/electrolyte interface cannot be the rate determining step of the electrode reaction at the three phase region of the reactant gas/porous electrode/solid electrolyte. Applying the reported model [ 5 1, the overpotential, q, is related to oxygen activity, aO, in YSZ at the electrode/ YSZ interface and the oxygen partial pressure, PO,, in the gas phase by the equation
416
q=RT/2Fln
A. Sawata et al. /Oxygen potential projile in SOFC
(ao/P&{2),
where a, in the oxide in equilibrium with gas is taken as unity. Using eqn. ( 1), the ships between steady-state current density, can be substituted for those between Z and
(1) 1 atm O2 relationZ, and r~ a,.
2.2.3. Rate equation for the fuel electrode For the case of H,-H20, Pt/YSZ system, the apparent reaction orders for PH2, m and n, seem to change with PH2 [4]. By the mathematical analysis of the polarization curves obtained for PH2> 10m2 atm, m, n, r, s, p and q of eq. (4’ ) were determined as 141
2.2. Rate equations
I=kH(PH~P~~~2Ka,-PH,oP&‘~2(Kao)-’~2},
2.2.1. General expressions for the rate equations at the SOFC electrodes When the rate determining step of the electrode reaction is not the charge transfer reaction, the reaction rate between gas phase and solid electrolyte can be described by the activity of the chemical species in the reaction process [ 61. Therefore, the current at the air and fuel electrodes can be expressed by the generalized equations I=k,{PG,“ag-P&,a,q}, for the air electrode,
(2) and
I=kH(P;;2PHPOab-PH:P;FIZOao”~
(2’)
for the fuel electrode, where ko and kH are the rate constants, PH2 and PHzo are the partial pressures of hydrogen and water vapor in Hz-H20 gas mixtures and m, n, p, q, r and s are the orders of the reaction for respective components. Because eqs. (2) or (2’ ) represent only one-reaction process, the order of forward reaction must be the same as the order of the backward reaction. Then, we have 2(m+n)=p+q for the air electrode m+n=r+s=p+q
(3) and (3’)
for the fuel electrode. 2.2.2. Rate equation for the air electrode By the mathematical analysis using eqns. ( 1) and (2), the orders of m, n, p and q were determined from the PO, dependence of steady-state polarization current on the air electrodes of O2 (g) /La0.&+,Mn03/ YSZ [ 31. The empirical rate equation was determined as (4)
where K is the equilibrium system [ 7 1. K=P,,ol
constant
(5)
of Hz-H20-O2
CPb’z*f’d
(6)
2.3. Electrode interface conductivity 2.3.1. Definition of the electrode interface conductivity In many studies, complex impedance techniques are employed for the measurements of electrode properties. From the impedance arcs obtained by the complex impedance measurement, we can determine the electrode interface resistance, RE, due to the overpotential at the electrode/electrolyte interface. The electrode interface conductivity, I&, is defined by the equation aE=l/ARE,
(7)
where A is area of the electrode/YSZ also given by 0,
=
(az/@),,,
interface.
.
GE is
(8)
2.3.2. Determination of k, and kH from 0~(0), a,(H) As shown by eq. ( 1 ), when q= 0, the equilibrium holds between a0 in YSZ interface and PO, in the gas phase. Then we have a0- -P&/2
.
(9)
Applying eqs. ( 1 ), (4) and ( 5) to eq. (8 ) and using eqs. (6) and (9), we obtain the relationships between the interface conductivity and the rate constant: (10) (11)
A. Sawataet al. /Oxygen potentialprofilein SOFC
Both eqs. ( 10) and ( 11) are consistent with the results of impedance measurements [ 3,4]. Thus, when oE( 0) and c+(H) are given from measurements of the interface impedance, we can calculate k. and kH by eqs. (10) and (11).
417 -interface
E
YSZ
45 Q
0
0
N
t
+
3. Oxygen chemical potential
2 V n_
profiles in SOFC
a&W=
!$gLL ‘01
/I
lOS/cnl2
10.
50
.
In discharging state of SOFC, the whole electrochemical reaction, proceeding across the electrode/ electrolyte interfaces and the electrolyte, takes place with the gradient of oxygen chemical potential, h, as the driving force. With eqs. (4) and (5), we can calculate the changes in ,uo at the electrode/YSZ interfaces as a function of current density. The relative oxygen chemical potential, Ah, is given by (ao/P;\‘2),
A,uo=po-&=RTln
r
> ":
100
0
5
150
2 z c" 200
:20z s x30? 40-
250 50-
(12)
where ,u& is h of the oxygen partial pressure in the reference gas, P&. Substituting Ab for a, of eqs. (4) and (5) with the help of eq. ( 12), the relation between I and Ah is expressed as,
Fig. 1. b profiles with various ~~(0) in the air electrode/YSZ interface under the current of I=200 mA/cm’ at 1000°C.
+terface
-exp(
-ACLo(O)IRT)}
(13)
for eq. (4), and
-exp[-&dH)I2RTlI
(14)
for eq. (5), where A&(O) and Ah(H) are the relative & to P& ( = 0.2 1 atm) in air and to P& in the H2-H20 gas mixtures, respectively. For given aE( 0) and GE(H ), k,, and kH can be determined from eqs. (10) and (11). Then,using eqs. (13) and (14), A&( 0) and A& (H ) can be calculated for any steady-state current. Figs. 1 and 2 show the h(O) and b(H) profiles, respectively, at the electrode/YSZ interface as a
bthode
tained by %athode
=bo(o)/2F
,0.5
1
5 10
and r,~,,,~~in figs. 1 and 2 were obFig. 2. h profiles with various a,(H) in the fuel electrode/YSZ interface under the current of I= 200 mA/cm* at 1000°C. Ratio of the fuel gas composition: HZO/H2 = l/9.
A. Sawata et al. /Oxygen
418
fuel
potential profile in SOFC
air electrode
electrode
Fig. 3. Steady-state oxygen chemical potential profiles in SOFC under the different current density (mA/cm2): (-) 0 (open circuit, approximation), (- - -) 50, (*-a-) 150, (*-*e-) 250 at 1000°C. The interface conductivities of fuel and air electrode: +(H) =O.l S/cm*, c+(O) = 1 S/cmZ.
and rlanode=Mo(H)I2F.
(15)
In figs. 1 and 2, log PO, is also indicated, which shows the effective PO, corresponding to the h in the cell. As shown in figs. 1 or 2, when a,< 1 S/cm’, the effective PO, at the interface is different by two or three orders of magnitude from the PO, of outer gas phase. Fig. 3 shows overall steady-state oxygen potential profiles in a SOFC as a function of current density at 1000°C for r&(O)= 1 S cm-* and o,(H)=O.l S cm-*. For simplicity, in this paper, we employ the approximation that the k profiles in YSZ are linear, as shown in fig. 3. Because the ionic transport number in YSZ is close to unity and the electronic conductivity is very small for 1O-)O
tiles in fig. 3 holds under the conditions with the steady-state current density of the order of mA and the more [9]. However, for the open circuit condition and under very small current of, maybe, less than 1 mA/cm*, the fi profiles deviates from the linear relationships. In this paper, we do not mention the further details of the chemical potential profiles in the YSZ layer because the precise calculation procedures for the ~0 profiles in the bulk YSZ were already given by Choudhury and Patterson [ 91.
4. Simulation of electrochemical characteristics Using the difference of h in YSZ between the two electrode interfaces, Ah (YSZ), the output voltage, E, of SOFC under steady-state current, I, is given by
419
A. Sawata et al. /Oxygen potential profile in SOFC
____-_:
100
- -.---___:
200
__--_--___: 500 lOOO”C,
0.6
air;Po2=0.2latm a02-‘0.
lScm-1
L 50
I
I
I
0
100
1
l50 i/
-2
200
I
250
300
mAcm
r
0 a I
-
1000°C.
100
Fig. 4. Simulated
___---: 200 __________-: 500 air: Po2=0.2latm. cIo2_=0.1Scm -I
fuel;
,PH20/P,2’1/9
: o.7w
1
I-V relationships
E= A~(YSZ)/2F-iL/ao~-
7
-.__
of a SOFC for different
,
electrolyte
(19)
where L is the thickness and ao2_ is the oxide ion conductivity of YSZ. Ah(YSZ) under steady-state is calculated by subtracting Ab( 0) and Ah(H) from Ah(YSZ) of the open circuit condition. Fig. 4 shows the steady-state I-Ah and I-E curves of SOFC at 1000°C with a,(O), r+(H) and L as pa-
thickness.
rameters. Here, the composition of H,O/H, gas mixtures was taken as l/9 and uoz- was fixed as 0.1 S/ cm. With the simulation described in this paper, when aE (0 ), oE( H) and ao2- are given, we can determine the limit of electrolyte thickness for the SOFC of desired Z-V characteristics. This simulation would be useful for the designing of SOFC cell construction.
420
A. Sawata et al. /Oxygen
[ I] J. Mizusaki, H. Tagawa, K. Tsuneyoshi, K. Mori and A. Sawata, Nippon Kagaku Kaishi (1988) 1623. [2] J. Mizusaki, H. Tagawa, K. Tsuneyoshi and A. Sawata, in: Proc. 1st Intern. Symp. SOFC, ed. S.C. Singhal, Vol. 89-l 1 (The Electrochem. Sot., NJ, 1989) pp. 254-264. [3] K. Tsuneyoshi, K. Mori, A. Sawata, J. Mizusaki and H. Tagawa, Solid State Ionics 35 (1989) 263. [ 41 J. Mizusaki, H. Tagawa, I. Koshiro, K. Isobe, K. Hirano and K. Fueki, presented at the 56th meeting of ECS Japan ( 1989) lG32, to be published.
potential
profile in SOFC
[ 5 ] J. Mizusaki, K. Amano, S. Yamauchi and K Fueki, Solid State Ionics22 (1981) 313. [6] H. Kobayashiand C. Wagner, J. Chem. Phys. 26 (1957) 1609. [7] M.W. Chase, Jr., C.A. Davies, J.R. Downey, Jr., D.J. Frurip, R.A. McDonald and A.N. Syverud, JANAF Thermochemical Tables, 3rd Ed., J. Phys. Chem. Ref. Data 14, Suppl. 1 ( 1985). [ 81 W. Weppner, J. Solid State Chem. 20 ( 1977) 305. [ 9 ] N.S. Choudbury and J.W. Patterson, J. Electrochem. Sot. 118 (1971) 1398.