Thin film ceria-bismuth bilayer electrolytes for intermediate temperature solid oxide fuel cells with La0.85Sr0.15MnO3-δ-Y0.25Bi0.75O1.5 cathodes

Article abstract of DOI:10.1016/j.materresbull.2010.01.013

Thin film electrolytes of bilayer bismuth oxide/ceria are developed for intermediate temperature solid oxide fuel cells. Y_0.25Bi_0.75O_1.5 is deposited via Direct Current magnetron sputtering technique on an Sm_0.2Ce_0.8O_1.90 electrolyte film which is prepared by a dry-pressing process on an NiO-Sm_0.2Ce_0.8O_1.90 substrate. La_0.85Sr_0.15MnO_3-δ-Y_0.25Bi_0.75O_1.5 composite is applied onto the Y_0.25Bi_0.75O_1.5 film as the cathode to form a single cell. Cells with 6-μm-thick Y_0.25Bi_0.75O_1.5 and 26-μm-thick Sm_0.2Ce_0.8O_1.90 bilayer electrolytes exhibit improved open circuit voltages and power density compared with those obtained with only Sm_0.2Ce_0.8O_1.90 electrolytes. The open circuit voltages are comparable and power densities are higher than those previously reported for solid oxide fuel cells with thick bilayer electrolytes using noble metals such as Pt as the electrodes. Impedance spectra show that the change of electrolyte resistance is negligible while the cathodic interfacial polarization resistance decreased significantly when the Y_0.25Bi_0.75O_1.5 layer is added to form the Sm_0.2Ce_0.8O_1.90/Y_0.25Bi_0.75O_1.5 bilayer electrolytes.

Full text of DOI:10.1016/j.materresbull.2010.01.013

Materials Research Bulletin 45 (2010) 603–608
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Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Thin film ceria–bismuth bilayer electrolytes for intermediate temperature solid
oxide fuel cells with La0.85Sr0.15MnO3À –Y0.25Bi0.75O1.5 cathodes
d
Lei Zhang a, Changrong Xia a, , Fei Zhao a,b, Fanglin Chen b
*
a CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China, No. 96,
Jinzhai Road, Hefei 230026, Anhui, China
b Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208, USA
A R T I C L E I N F O
A B S T R A C T
Article history:
Thin film electrolytes of bilayer bismuth oxide/ceria are developed for intermediate temperature solid
oxide fuel cells. Y0.25Bi0.75O1.5 is deposited via Direct Current magnetron sputtering technique on an
Sm0.2Ce0.8O1.90 electrolyte film which is prepared by a dry-pressing process on an NiO–Sm0.2Ce0.8O1.90
Received 4 September 2009
Received in revised form 30 December 2009
Accepted 18 January 2010
Available online 28 January 2010
substrate. La0.85Sr0.15MnO3À –Y0.25Bi0.75O1.5 composite is applied onto the Y0.25Bi0.75O1.5 film as the
d
cathode to form a single cell. Cells with 6-mm-thick Y0.25Bi0.75O1.5 and 26-mm-thick Sm0.2Ce0.8O1.90
bilayer electrolytes exhibit improved open circuit voltages and power density compared with those
obtained with only Sm0.2Ce0.8O1.90 electrolytes. The open circuit voltages are comparable and power
densities are higher than those previously reported for solid oxide fuel cells with thick bilayer
electrolytes using noble metals such as Pt as the electrodes. Impedance spectra show that the change of
electrolyte resistance is negligible while the cathodic interfacial polarization resistance decreased
significantly when the Y0.25Bi0.75O1.5 layer is added to form the Sm0.2Ce0.8O1.90/Y0.25Bi0.75O1.5 bilayer
electrolytes.
Keywords:
A. Ceramic
A. Thin film
B. Sputtering
C. Electrochemical measurements
D. Electrochemical properties
ß 2010 Elsevier Ltd. All rights reserved.
1. Introduction
zirconia (YSZ) and scandium stabilized zirconia (ScSZ). ZrO2-based
electrolytes show excellent stability under reducing atmosphere
The major challenge for solid oxide fuel cells (SOFCs)
commercialization is to lower its operating temperature to an
conditions, and thus are often applied in the electrolyte facing the
fuel side while ceria is exposed to the air side.
intermediate range of 500–800 8C while still maintaining
a
Bismuth-based electrolytes have also been considered as the
electronic barriers for doped ceria. Low electrolyte ohmic
resistance is expected by using bismuth-based electrolytes whose
conductivities are about two orders of magnitude higher than
those of zirconia-based electrolytes. However, bismuth-based
electrolytes could decompose to metallic bismuth in the presence
of the reducing agent such as H2 or CH4 [11]. Therefore, they could
not be used to face the fuel side as the zirconia-based material
does. On the contrary, the bismuth-based material can be exposed
to the air side since it is expected to be a pure oxide ionic conductor
and thermodynamically stable under oxygen partial pressure
down to 10À13 atm [12,13]. Some reports even show that bismuth-
based materials are stable under oxygen partial pressure as low as
10À20 atm [14]. Consequently, bilayer structure using ceria and
bismuth-based material is expected to show the advantages of
both cerium and bismuth electrolytes: the ceria layer prevents the
comparable cell performance. By reducing the temperature,
metallic materials can be employed to reduce the cost, and
retardant degradations of materials can increase the fuel cell
lifetime [1]. Nevertheless, lowering the operating temperature
causes several problems, including increased ohmic impedance
through the electrolyte and high over potentials through the
electrodes [2,3]. Alternative electrolytes such as doped ceria, which
have higher ionic conductivity than the conventional stabilized
zirconia, have therefore become more and more attractive.
However, ceria-based electrolytes for SOFCs operated at low-
and-intermediate temperatures are well-known to be reducible at
low oxygen partial pressures [4,5]. The reduction of ceria from Ce4+
to Ce3+ leads to current leakage with an n-type electronic
conduction, resulting in drop in open circuit voltages (OCVs)
[6,7]. Efforts have been made to block the current leakage, and thus
improve the OCV [8–10]. The most popular material as electronic
block layer is ZrO2-based material, such as yttria-stabilized
bismuth layer from decomposing at low PO while the bismuth
2
layer serves as the electronic barrier for the ceria layer.
With the cerium–bismuth bilayer as the electrolytes, increased
OCVs close to 1.0 V at 500 8C have been demonstrated with single
cells using hydrogen and air as the fuel and oxidant, respectively
[14–17]. High stability has also been reported for the bilayer
* Corresponding author. Tel.: +86 5513607475; fax: +86 5513601592.
E-mail address: xiacr@ustc.edu.cn (C. Xia).
0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2010.01.013

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L. Zhang et al. / Materials Research Bulletin 45 (2010) 603–608
electrolytes. Wachsman et al. have shown that the bilayer
electrolytes were stable under fuel cell operation conditions for
1400 h at temperatures in the range of 500–800 8C [14]. In
addition, Park et al. have claimed that no secondary phases with
lower conductivity are formed at the bilayer interface [16]. In these
and fired at 800 8C for 2 h to form porous LSM–YSB electrodes. The
electrode thickness was about 30 m.
m
Anode-supported single cells with NiO–SDC as the substrates
anodes and SDC as the electrolytes were fabricated using a co-
pressing method [21]. Anode precursors consisted of 60 wt% NiO
and 40 wt% SDC were mixed with an agate mortar. The mixed
powders were pre-pressed while SDC powder was subsequently
added on the top of the pre-pressed pellet and then co-pressed to
form the NiO–SDC/SDC substrates. The substrates were co-fired at
1250 8C for 5 h to densify the SDC electrolyte. YSB thin films were
then deposited on the SDC layers by a DC (Direct Current)
magnetron sputtering technique at room temperature under
oxygen and argon (30:70 vol%) pressure of 4 Pa. The NiO–SDC/
SDC pellets were positioned on a substrate holder with the draw
distance of about 50 mm. The sputtering was conducted for 1 h to
reports, thin films (0.2–6
mm) of Y or Er doped Bi2O3 were prepared
by Pulse Laser Deposition (PLD) on Y, Sm, or Gd doped ceria
substrates, which were 0.8–2.0 mm thick. At the same time, thick
films of doped-Bi2O3 (5–60
mm thick) were prepared on the ceria
substrates with slurry-coating and dip-coating techniques. Anode-
supported fuel cells were developed with bilayer electrolytes
consisting of 84-
m
m-thick GDC (Gd0.1Ce0.9O1.95) and 16-
mm-thick
YSB (Y0.25Bi0.75O1.5
)
and generated peak power density of
260 mW cmÀ2 at 700 8C. The authors suggested that the power
density might be significantly improved by using a thinner bilayer
electrolyte [15]. Recently, Ahn et al. have applied Bi2Ru2O7–
Er0.8Bi1.2O3 cathode on ESB/GDC (Gd0.1Ce0.9O2) bilayer electro-
lytes, and produced exceptionally high performance with maxi-
mum power density of 1.95 W cmÀ2 at 650 8C [18].
form 6
mm YSB layer. The resulted trilayer NiO–SDC/SDC/YSB was
annealed in air at 800 8C for 2 h. LSM–YSB cathodes were then
applied by the screen-printing method and fired at 800 8C for 2 h.
In this work, single cell without YSB layer, NiO–SDC/SDC/LSM–YSB,
is termed as Monolayer cell while the cell with YSB electrolyte,
NiO–SDC/SDC/YSB/LSM–YSB, as Bilayer cell.
In the previous reports on the cerium–bismuth bilayer
electrolytes, fuel cells are usually constructed with Pt or Au as
the electrodes, mainly due to the fact that many strontium
cobaltite cathode materials such as La0.6Sr0.4Co0.2Fe0.8O3 and
Sm0.5Sr0.5CoO3 could react with bismuth oxides at the temperature
when the fuel cells are fabricated [19]. Our recent work shows that
2.3. Characterization
The phase structure was identified by powder X-ray diffraction
(XRD) with a Philips X’pert PRO diffractometer. Morphology and
microstructure were obtained by scanning electron microscope
(SEM) technique using a FEI XL30 Environmental scanning electron
microscope. Electrochemical measurements were conducted with
a Zahner Im6ex electrochemical workstation. The impedance of
symmetrical cells was measured using a two-probe impedance
method with Ag paste and Ag wires as current collector and leads.
The measurements were taken in ambient air in the frequency
range from 0.01 Hz to 1 MHz with a bias voltage of 10 mV over a
temperature range of 550–650 8C.
bismuth oxide and LSM (La0.85Sr0.15MnO3À
) are chemically
d
compatible under operating conditions for low-and-intermediate
temperature SOFCs [20].
In this work, we studied anode-supported SOFCs with thinner
bilayer electrolytes consisting of 26-mm-thick SDC and 6-mm-
thick YSB to increase the cell performance and to reduce the
operating temperatures. The cells were constructed without using
noble metal electrodes but with Ni–SDC as the anodes and LSM–
YSB as the cathodes.
2. Experimental
Single cells were attached and sealed on an alumina tube using
Ag paste, with humidified hydrogen (3% H2O, 60 ml minÀ1) as the
fuel and the ambient air as oxidant. Fuel cell performances were
measured with a galvanostatic mode at temperatures of 550, 600,
and 650 8C. The measurement was conducted 30 min after the cell
was heated to the operation temperature.
2.1. Powder preparation
Powders of SDC, LSM, NiO, and YSB were synthesized using a
glycine-nitrate combustion method with nitrate precursors of
Sm(NO3)3, (NH4)2Ce(NO3)6, La(NO3)3, Sr(NO3)3, Mn(NO3)2,
Ni(NO3)2, Y(NO3)3, and Bi(NO3)3 [20]. Stoichiometric amounts of
the nitrate were dissolved in distilled water, to which glycine
(NH2–CH2–COOH) was added. The solution was stirred for several
hours while heated on a hot plate to convert it to a viscous gel, and
then further heated to spontaneous ignition, resulting in homoge-
neous ashes. The ash was subsequently calcined at high
temperatures to remove possible organic residues and to form
the desired crystalline structures. The heating temperatures and
time for SDC, LSM, NiO, and YSB powders were 600 8C 2 h, 900 8C
4 h, 850 8C 4 h and 600 8C 2 h, respectively.
3. Results and discussion
3.1. Microstructure characterization
XRD measurements show that the sputtered YSB film presents
pure cubic phase, as shown in Fig. 1. Wachsman et al. reported
that no parasitic instability had been observed for the bilayer SDC/
ESB electrolytes when they were operated at 650 8C over 1250 h
under open circuit conditions [14]. Park et al. have shown that the
interface between SDC and doped Bi2O3 is stable when the bilayer
is fired at 890 8C for 10 h [16]. Therefore, it is assumed that the
reactivity between the SDC and YSB layers is negligible based on
the prior work.
2.2. Cell preparation
Symmetrical cells were constructed with LSM–YSB composite
electrodes on SDC and YSB electrolytes. The SDC and YSB powders
were cold-pressed to form disks with diameter of 15 mm. In order
to obtain dense substrate, the SDC disks and YSB disks were fired at
1400 8C for 5 h and 800 8C for 2 h, respectively. To prepare the
LSM–YSB composite cathode, LSM and YSB powders in weight ratio
of 1:1 were mechanically mixed with an organic binder (a-
terpineol as the solvent, ethyl cellulose as the binder) to form a
slurry (with weight ratio of 1:1.5). The slurry was applied to both
sides of the SDC and YSB substrates using a screen-printing
technique. The printed layers were dried under an infrared lamp,
Fig. 2 is the cross-sectional view of the Bilayer cell. Shown in
Fig. 2a is the interface between cathode and electrolyte, which is
well bonded to each other. Fig. 2b shows the cross-sectional view
of the bilayer electrolyte. The SDC electrolyte is fairly dense with a
few isolated closed pores. The grain size is about 1
thickness of SDC layer is about 26 m. The sputtered YSB layer is
about 6 m in thickness. It is also fairly dense, crack-free, and with
only a few isolated pin-holes. The YSB grains are cubic in shape
with an average size of 0.5 m. Excellent bonding has been formed
mm. The
m
m
m
and there is no clearly observable interface between the two layers
in the electrolytes. The YSB layer could be distinguished from the

L. Zhang et al. / Materials Research Bulletin 45 (2010) 603–608
605
Fig. 1. XRD pattern of sputtered YSB, which was annealed at 800 8C for 2 h.
SDC by the difference in the particle size. Fig. 2c is an enlarged
image of the LSM–YSB cathode. The cathode consists of microme-
ter scale LSM particles and sub-micron YSB particles. The LSM
particles are porous and the YSB particles are cubic shaped.
3.2. Fuel cell performance
Fig. 3a shows the cell voltage and power density versus current
density for the Monolayer and Bilayer cells, which were operated
at 650 8C with humidified (3% H2O) hydrogen on the anode side
and stationary air on the cathode side. The Monolayer cell
exhibited open circuit voltage (OCV) of 0.779 V at 650 8C. The
OCV is consistent with that reported for H2/air fuel cells using thin
layer SDC electrolytes [18,20]. When 6-mm-thick YSB was added,
the OCVs increased to 0.852 V, displaying an increase in OCV
compared to that of the Monolayer cell. The increase in OCV is due
to the blocking of the electronic transport by the sputtered YSB
layer. At 550 8C and 600 8C, OCVs for Bilayer cell are 0.929 and
0.897 V, while for Monolayer cell those are a little lower of 0.909
and 0.880 V. It is noted that the increase in OCV is more
pronounced at high temperature; it is 0.020 V at 500 8C and
0.073 V at 650 8C. This is because the reduction of Ce4+ to Ce3+ is
more serious at high temperatures, and the Ce4+/3+ equilibrium
results in decreased ionic domain of ceria electrolytes with the
increase in temperatures [22].
The OCVs obtained with the Bilayer cell are close to those
reported for H2/air fuel cells with ceria–bismuth bilayer electro-
lytes, as shown in Table 1. For example, Park and Wachsman [17]
observed an OCV of 0.783 V at 600 8C for fuel cells based on bilayer
Fig. 2. SEM micrographs of single cells with and without YSB layer: (a) cross-section
of Bilayer cell with LSM–YSB cathode; (b) cross-section of the bilayered
electrolytes; (c) the enlarge image of the LSM–YSB cathode.
electrolytes consisting of 9-
Leng and Chan [15] obtained an OCV of 0.885 V at the same
temperature using an 84- m-thick GDC electrolyte with a 16- m-
thick YSB as the blocking layer. In this work, OCV of 0.897 V was
achieved at 600 8C using a much thinner bilayer electrolyte
mm-thick ESB and 1.5-mm-thick SDC.
m
m
285 mW cmÀ2 for Monolayer cell (Fig. 3a). The combination of
a higher OCV by blocking electronic transport in ceria electrolyte
and a lower electrolyte resistance by using thinner YSB layer
results in superior power density in the Bilayer cells compared
with that of the Monolayer cells. In addition, the use of thinner
bilayer electrolyte results in power density much higher than those
reported in the literature. For comparison, the highest powder
density reported for the Bilayer cells is 125 mW cmÀ2 at 600 8C
[15]. It should be noted that the high performance was obtained
without using noble metal electrodes in this work while the
previously reported fuel cells were constructed with one or two
electrodes using noble metals such as Pt and Au as shown in
Table 1. In this work, Ni–SDC and LSM–YSB were used as the
anodes and cathodes, respectively. The use of oxide electrodes will
reduce the overall cost of the fuel cell.
consisting of 6-mm-thick YSB and 26-mm-thick SDC. The
comparatively high OCV obtained in this work demonstrates that
it is feasible to use thinner bilayer electrolytes. Decrease in
electrolyte thickness could effectively reduce SOFC operation
temperatures.
Fig. 3b shows the cell voltage and power density versus current
density for the Bilayer cells, which were operated at 550 8C, 600 8C
and 650 8C. The Bilayer cell generated peak power density of 153,
266, and 381 mW cmÀ2 at 550, 600, and 650 8C, respectively,
which are much higher than those produced by the Monolayer cell.
For example, the peak power density for Bilayer cell is
381 mW cmÀ2 for Bilayer cell at 650 8C, while it is only

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L. Zhang et al. / Materials Research Bulletin 45 (2010) 603–608
Fig. 4. Power density versus operating time with a constant voltage output of 0.5 V
at 600 8C.
ohmic resistances, Ro, and the intercepts between low and high
frequency to the interfacial polarization resistance, Rp, which is
contributed by both the cathode and anode [26]. Ro is almost the
same for the two cells, implying that under the fuel cell operating
conditions, the addition of a 6-mm-thick YSB layer to the 26-mm-
thick SDC layer has negligible effect on the electrolyte resistance.
The conductivity of YSB electrolyte is more than two times higher
than that of the SDC electrolyte at temperature between 550 and
650 8C [22]. The contribution of thin film YSB to Ro could therefore
be ignored. The similarity in Ro of the Monolayer and Bilayer cells
also indicates that no insulating phases have been formed between
the SDC and YSB layers during the cell fabrication process. At the
same time, Rp on the cells with bilayer electrolyte is still small,
implying that the SDC layer has successfully prevented YSB film
from exposure to the reducing gas and avoided the formation of
metallic bismuth with large resistance [12]. Thus, thermodynamic
stability of the YSB layer can be maintained if it is not exposed to an
Fig. 3. Cell voltage and power density as a function of current density when
humidified H2 (3% H2O, 60 mL minÀ1) was used as the fuel and ambient air as the
oxidant: (a) the Monolayer and Bilayer cells measured at 650 8C; (b) Bilayer cell
measured at 550 8C, 600 8C, and 650 8C.
The durability of a Bilayer cell was investigated under a cell
potential of 0.50 V at 600 8C, Fig. 4. In the initial state of the
constant voltage test, the power density increased with time and
reached 430 mW cmÀ2 in 14 h. The increase might be caused by
the activation effect of the LSM-based cathode [23–25]. The effect
is believed to reduce the interfacial polarization resistance. After
15 h, the power density declined with testing time, which might be
due to the degradation of electrode and/or electrolyte materials.
However, the power density maintained above 300 mW cmÀ2
during the 100-h measurement.
atmosphere with PO lower than the bismuth oxide decomposition
2
PO . In the work of Leng and Chan, Rp of 0.395
V
cm2 is reported at
2
700 8C for Pt cathode, which is even higher than that obtained at
650 8C in this work. The utilization of LSM–YSB cathode has
effectively lowered the interfacial polarization resistance Rp.
Under open circuit conditions, the Bilayer cell exhibited higher
Rp than the Monolayer cell at every measured temperature. The
anodic interfacial polarization resistance should be the same for
the two cells since the anodes were fabricated with the same
procedures. Therefore, the difference in Rp could be attributed to
the difference in the cathode interfacial polarization resistance, Rc.
Often, when the electrolyte conductivity is higher, a cathode
exhibits lower Rc than that when the conductivity is lower [27].
That is to say, Rc of the Bilayer cell, the interfacial polarization
resistance between the LSM–YSB cathode and YSB electrolyte,
should be lower than that of the Monolayer cell, the resistance
3.3. Interfacial polarization resistance under open circuit conditions
Fig. 5 shows the impedance spectra of the two single cells
measured under open circuit conditions at 550, 600, and 650 8C.
The first intercept on the real-axis at high frequency corresponds to
Table 1
Electrolytes thickness and OCVs in different bilayer electrolytes single cells measured at 600 8C [14,15,17].
Anodes
Electrolytes
Layer 1
Cathodes
OCV (V)
Reference
Thickness
Layer 2
Thickness
5–60
Pt
YDC (SDC, GDC)
0.8–1.0 mm
1.5 mm
ESB
ESB
ESB
YSB
YSB
m
m
Au
0.901–0.977
0.783
14
Pt
SDC
SDC
GDC
SDC
9
mm
Au
17
Pt
1.5 mm
22
16
m
m
Ag–ESB
Pt
0.949
17
Ni–GDC
Ni–SDC
84
26
m
m
m
m
mm
0.885
15
6
mm
LSM–YSB
0.897
This work

L. Zhang et al. / Materials Research Bulletin 45 (2010) 603–608
607
decreased the total cell resistance, which is consisted with the
results reported by Ahn et al. [18]. The variation in Rt is mainly
determined by Rp. The decreased Rp by using bilayer electrolyte is
most likely due to the high oxygen ion conductivity of YSB [27] and
the chemical compatibility between the LSM–YSB cathode and YSB
electrolyte, which will be further supported by the symmetrical
cells.
3.5. Cathode interfacial polarization resistances measured with
symmetrical cells
The improvement of LSM–YSB performance by introducing a
YSB layer was further investigated using symmetrical cells of
LSM–YSB/YSB/LSM–YSB and LSM–YSB/SDC/LSM–YSB. Fig.
7
shows the Arrhenius plots of area specific resistance (ASR). ASR
for the interface between an LSM–YSB electrode and a YSB
electrolyte is much lower than that between the LSM–YSB
electrode and an SDC electrolyte in the temperature range of
500–700 8C 8C. For example, at 600 8C ASR measured on SDC
electrolyte is 1.03
V V
cm2 while it is only 0.40 cm2 on YSB
electrolyte. The activation energy for ASR is also low with the YSB
electrolyte. The low ASR with YSB is due to the high conductivity of
YSB since ASR usually increases with the electrolyte resistivity.
The relationship can be theoretically explained by the non-
uniform electrode theory [27,30]. Further, the YSB electrolyte
shows better thermal and chemical compatibility with the LSM–
YSB cathode, since YSB is present in both the electrode and
electrolyte.
Fig. 5. AC impedance spectra of the Bilayer and Monolayer cells measured at 550 8C,
600 8C, and 650 8C.
between LSM–YSB electrode and SDC electrolyte. However, the
measured Rc is higher for the Bilayer cell. This could be caused by
the electronic transport as a result of Ce4+ reduction to Ce3+ under
reducing conditions [19]. It has been demonstrated that Rc
determined by the impedance spectrum is lower than the real
interfacial polarization resistance when the electrolyte is a mixed
electronic and oxide ionic conductor [28]. In addition, the
electronic transport causes internal shorting, which means current
is passing through the electrodes although the cell is under open
circuit conditions. The current activates LSM-based cathode [23–
25] and thus reduces Rc. It is expected that the Monolayer cell
should have much larger Rp than that shown in Fig. 5 if Ce4+ were
not reduced. Therefore, the higher Rp of the Bilayer cell shown in
Fig. 5 indicates that the electronic conduction in the bilayer
electrolyte is effectively blocked by the YSB layer.
3.4. Interfacial polarization resistances under loading
The total cell resistances, Rt, under loading can be determined
with the I–V curves as shown in Fig. 3. The slope of the I–V curve is
influenced greatly by the current density. At low current density
value, it is usually dominated by activation polarization. At a
moderate value, it represents the sum of the electrolyte resistance,
Ro and the interfacial polarization resistance, Rp [29]. In this work,
Rt is obtained when the current density exceeded 0.3 A cmÀ2. The
electrolyte resistance is not affected by the current density and
thus can be determined with the impedance spectrum. Therefore,
Rp under loading can be obtained, Rp = Rt À Ro.
Fig. 6. (a) the total cell resistance Rt determined from the impedance spectra; (b) the
interfacial polarization resistance Rp calculated from Rp = Rt À Ro on Monolayer cell
and Bilayer cell.
Fig. 6 shows Rt and Rp of the Bilayer and Monolayer cells under
loading. The addition of an YSB layer did not increase but rather

608
L. Zhang et al. / Materials Research Bulletin 45 (2010) 603–608
by the Natural Science Foundation of China (10979046 and
50730002) and the Ministry of Science and Technology of China
(2007AA05Z151). F. Zhao and F.L. Chen were supported as part of
Science Based Nano-Structure Design and Synthesis of Heteroge-
neous Functional Materials for Energy Systems, an Energy Frontier
Research Center funded by the U.S. Department of Energy, Office of
Science, Office of Basic Energy Sciences under Award Number DE-
SC0001061.
References
[1] M. Dokiya, Solid State Ionics 152 (1997) 383–392.
[2] S. Souza, S.J. Visco, L.C. Jonghe, Solid State Ionics 98 (1997) 57–61.
[3] P.K. Srivastava, T. Quach, Y.Y. Duan, R. Donelson, S.P. Jian, F.T. Ciacchi, S.P.S.
Badwal, Solid State Ionics 99 (1997) 311–319.
[4] B.C.H. Steele, Solid State Ionics 129 (2000) 95–110.
[5] N.M. Sammes, G.A. Tompsett, H. Na¨fe, F. Aldinger, J. Eur. Ceram. Soc. 19 (1999)
1801–1826.
[6] A. Atkinson, Solid State Ionics 95 (1997) 249–258.
[7] S.P.S. Badwal, F.T. Ciacchi, J. Drennan, Solid State Ionics 121 (1999) 253–262.
[8] T. Tsai, E. Perry, S. Bernett, J. Electrochem. Soc. 144 (1997) L130–L132.
[9] D.F. Yang, X.G. Zhang, S. Nikumb, C.D. Petit, R. Hui, R. Maric, D. Ghosh, J. Power
Sources 164 (2007) 182–188.
[10] Q.L. Liu, K.A. Khor, S.H. Chan, X.J. Chen, J. Power Sources 164 (2007) 182–188.
[11] H. Kruidhof, K.J. De Vries, A.J. Burggraaf, Solid State Ionics 37 (1990) 213–215.
[12] E.D. Wachsman, G.R. Ball, N. Jiang, D.A. Stevenson, Solid State Ionics 52 (1992)
213–218.
Fig. 7. Arrhenius plots of interfacial polarization resistance of LSM–YSB cathodes
measured with symmetrical cells supported on SDC and YSB substrates.
[13] P. Duran, J.R. Jurado, C. Moure, N. Valverde, B.C.H. Steele, Mater. Chem. Phys. 18
(1987) 287–294.
[14] E.D. Wachsman, P. Jayaweera, N. Jiang, D.M. Lowe, B.G. Pound, J. Electrochem. Soc.
144 (1997) 233–236.
4. Conclusion
Anode-supported single cells with La0.85Sr0.15MnO3À
0.25Bi0.75O1.5 ceramic cathode on Sm0.2Ce0.8O1.90/Y0.25Bi0.75O1.5
bilayer electrolytes were developed. The additional Y0.25Bi0.75O1.5
film could sufficiently block the electronic transport of ceria-based
electrolytes, and thus increase the open circuit voltages. Using
–
[15] Y.J. Leng, S.H. Chan, Electrochem. Solid-State Lett. 9 (2006) A56–A59.
[16] J.Y. Park, H. Yoon, E.D. Wachsman, J. Am. Ceram. Soc. 88 (2005) 2402–2408.
[17] J.Y. Park, E.D. Wachsman, Ionics 12 (2006) 15–20.
[18] J.S. Ahn, D. Pergolesi, M.A. Camaratta, H. Yoon, B.W. Lee, K.T. Lee, D.W. Jung, E.
Traversa, E.D. Wachsman, Electrochem. Commun. 11 (2009) 1504–1507.
[19] V.V. Kharton, E.N. Naumovich, V.V. Samokhval, Solid State Ionics 99 (1997) 269–
280.
[20] Z.Y. Jiang, L. Zhang, K. Feng, C.R. Xia, J. Power Sources 185 (2008) 40–48.
[21] C.R. Xia, M.L. Liu, Solid State Ionics 144 (2001) 249–255.
[22] H. Inaba, H. Tagawa, Solid State Ionics 83 (1996) 1–16.
[23] S.P. Jiang, J.G. Love, J.P. Zhang, M. Hoang, Y. Ramprakash, A.E. Hughes, S.P.S.
Badwal, Solid State Ionics 121 (1999) 1–10.
[24] X.J. Chen, K.A. Khor, S.H. Chan, Solid State Ionics 167 (2004) 379–387.
[25] S. McIntosh, S.B. Adler, J.M. Vohs, R.J. Gortea, Electrochem. Solid-State Lett. 7
(2004) A111–A114.
d
Y
La0.85Sr0.15MnO3À –Y0.25Bi0.75O1.5 composite instead of noble metals
d
as the cathode lowers the cell overpotential. Interfacial polarization
resistance of La0.85Sr0.15MnO3À –Y0.25Bi0.75O1.5 cathode is lower on
d
the Y0.25Bi0.75O1.5 electrolyte than that on Sm0.2Ce0.8O1.90, resulting
in low cell resistance. The Bilayer cells thus show superior
performance including higher open circuit voltages and power
densities compared with that of the Monolayer cells.
[26] C.R. Xia, W. Rauch, W. Wellborn, M.L. Liu, Electrochem. Solid-State Lett. 5 (2002)
A217–A220.
[27] T. Kenjo, Y. Kanehira, Solid State Ionics 148 (2002) 1–14.
[28] M.L. Liu, H.X. Hu, J. Electrochem. Soc. 143 (1996) L109–L112.
[29] J.W. Kim, A.V. Virkar, K.Z. Fung, K. Mehta, S.C. Singhal, J. Electrochem. Soc. 146
(1999) 69–78.
Acknowledgements
We would like to thank Dr. Yunxin Han for performing the DC
magnetron sputtering depositions. Z. Lei, C.R. Xia were supported
[30] T. Kenjo, H. Tanabe, Y. Hoshiba, Solid State Ionics 159 (2003) 197–207.