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Effects of composite cathode on electrochemical
and redox properties for intermediate-temperature
solid oxide fuel cells
Changmin Kim a, Junyoung Kim a, Jeeyoung Shin b,**, Guntae Kim a,*
a
Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798,
Republic of Korea
b
Department of Mechanical Engineering, Dong-Eui University, Busan 614-714, Republic of Korea
abstract
Keywords:
A composite cathode composed of NdBa0.5Sr0.5Co1.5Fe0.5O5þd (NВSCF) and Ce0.9Gd0.1O1.95
Solid oxide fuel cells (SOFC)
(GDC) has been investigated to evaluate its electrochemical properties for intermediate-
Layered perovskite
temperature solid oxide fuel cells (IT-SOFCs) based on structural characteristics and oxy-
Composite cathode
gen redox stability. The composite cathode has a lower polarization loss than a pure NBSCF
Electrochemical performance
cathode because the specific addition of GDC provides extended electrochemically active
sites where the oxygen reduction reaction (ORR) occurs. Accordingly, the optimized NBSCF40GDC cathode material had the lowest ASR, 0.074 W cm2 at 873 K, resulting in excellent
cell performance of 1.83 W cm2 at 873 K. In particular, investigation into the oxygen redox
stability reveals that the composite cathode has superior redox stability under the operating conditions than a bulk NBSCF cathode material, which affects the long-term stability
of the cathode performance.
Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.
Introduction
Solid oxide fuel cells (SOFCs) are devices that convert chemical energy to electrical energy directly through electrochemical oxidation, providing advantages of fuel flexibility,
low pollutant emission, and high efficiency. The requirement
of high operating temperature of 1073e1273 K, however, gives
rise to considerable issues such as high costs and material
compatibility originating from the difference in the thermal
expansion coefficient (TEC). Significant efforts therefore have
been devoted to lowering the operation temperature of SOFCs
toward an intermediate range (873e1073 K) to enhance long-
term stability and economic feasibility. Lowering of the
operating temperature, however, results in serious problems
including degradation of the electrocatalytic activity over the
cathode, which is associated with the oxygen reduction reaction (ORR) [1e4].
In this regard, mixed ionic and electronic conductors
(MIECs) with perovskite oxides based on transition metal (e.g.
Mn, Fe, Co, and Ni) have been extensively researched as
promising cathode materials of IT-SOFCs, due to their capability to conduct electrons and oxygen ions [5]. Among the
various MIECs oxides, cobalt based perovskite oxides, such as
BaCoO3 [6], Sm0.5Sr0.5CoO3 [7], La0.6Sr0.4Co0.2Fe0.8O3d [8], and
* Corresponding author. Fax: þ82 52 217 2909.
** Corresponding author. Fax: þ82 51 890 2232.
E-mail addresses: jyshin@deu.ac.kr (J. Shin), gtkim@unist.ac.kr (G. Kim).
http://dx.doi.org/10.1016/j.ijhydene.2014.07.007
0360-3199/Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 4 ) 1 e7
Pr1xSrxCoO3d [9], have displayed excellent electrocatalytic
activity for the oxygen reduction reaction.
Recently, layered perovskite oxides have been studied as
novel cathode materials due to their remarkable oxygen kinetics rate relative to those of ABO3-type simple perovskite
oxides [10,11]. The general formula of the layered perovskite
oxides can be described as AA0 B2O5þd, where A ¼ trivalent
lanthanide ion (Ln ¼ Pr, Nd, Sm, and Gd), A0 ¼ Ba or Sr, and
B ¼ a first row transition metal ion or a mixture thereof. The
layered perovskite consists of two layers with alternating
stacking of … jAOjBO2jA0 OdjBO2j … along the c-axis. The
lanthanide layers provide mobile oxygen species channels by
reducing the oxygen bonding strength, which enhances oxygen ion diffusivity [11]. On the basis of these favorable properties of layered perovskite oxides, such as LnBaCo2O5þd
(Ln ¼ Pr, Nd, Sm, and Gd) layered perovskite oxides, several
groups have studied their capability as IT-SOFCs cathode
materials. Kim et al. [12] reported that PrBaCo2O5þd (PBCO) is a
promising material for IT-SOFC cathodes, as it showed a high
surface exchange coefficient and rapid oxygen ion diffusivity,
resulting in low cathodic polarization. The partial cosubstitution of Co for Fe and Ba for Sr, in particular, improves the ORR activity, electrical conductivity, oxygen ion
diffusivity, and stability of the cathode [13e18]. Upon this
background, our group reported the layered perovskite cathode materials, LnBa0.5Sr0.5Co1.5Fe0.5O5þd (Ln ¼ Pr and Nd),
which have high electrochemical performance with excellent
stabilities under operating conditions [19]. Based on a DFT
analysis presented in our previous study [19], the layered
structure provides pore channels for ion motion in the [LneO]
and [CoeO] planes, which could provide fast paths for oxygen
transport and these oxygen ion diffusion paths follow a
zigezag type trajectory through the CoeO plane perpendicular
to the Ln-O plane.
It has been reported that the composite cathode prepared
by specific addition of ionic conducting materials on a
MIEC cathode contributes to improvement of electrochemical
performance. Among these ionic conducting materials,
Ce0.9Gd0.1O1.95 (GDC) can improve the electrocatalytic activity
of the cathode by providing additional triple phase boundary
(TPB) sites where the electrochemical reaction occurs
[20,21]. Kim et al. [22] reported on the mechanism of the ORR
for a MIEC-GDC composite cathode consisting of
NdBa0.5Sr0.5Co2O5þd (NBSCO) and GDC. The authors reported
that the composite cathode has a lower polarization loss than
a pure NBSCO cathode due to the addition of GDC followed by
extension of the TPB sites.
Together with the substantial enhancement of single cell
performance of Fe doped NBSCO, NdBa0.5Sr0.5Co1.5Fe0.5O5þd
(NBSCF), long-term stability of the cell is also an important
requirement for IT-SOFCs [19]. Low p(O2) operation may cause
critical redox degradation of the cathode at the interface between the electrolyte and the cathode, which affects the longterm stability of the cathode performance [23,24]. Kim et al.
[25] reported that a ceria based YSZ electrolyte composite
anode exhibits enhanced reducibility relative to that of bulk
ceria. In this regard, improvement of oxygen redox properties
can be expected through the addition of an electrolyte material on the cathode. Meanwhile, there have been no reports on
the effects of NBSCF-GDC composite cathodes, particularly
regarding the oxygen redox stability of NВSCF. In this study,
therefore, we conducted a systematic investigation to optimize the electrochemical properties of the NBSCF cathode by
optimizing the ratio of GDC to NBSCF based on the structural
characteristics and oxygen redox stability of these materials.
Experimental
NdBa0.5Sr0.5Co1.5Fe0.5O5þd oxides were synthesized using the
Pechini process. Stoichiometric amounts of Nd(NO3)3$6H2O
(Aldrich, 99.9%, metal basis), Ba(NO3)2 (Aldrich, 99 þ %),
Sr(NO3)2 (Aldrich, 99 þ %), Co(NO3)2$6H2O (Aldrich, 98 þ %),
and Fe(NO3)3$9H2O (Aldrich, 98 þ %) were dissolved in distilled
water under continuous heating and stirring. A proper
amount of citric acid and ethylene glycol were added into the
beaker after the mixture was dissolved. After a viscous resin
was formed, the mixture was heated around 473 K. The
resultant products were pre-calcined at 873 K for 4 h, and ballmilled in acetone for 24 h. The pre-calcined NBSCF powder
and Ce0.9Gd0.1O1.95 (GDC) were mixed at weight ratio of 10:0,
8:2, 6:4, and 5:5 and ball-milled in acetone for 24 h. The abbreviations used to identify various samples are given in
Table 1. The mixtures of the NBSCF and GDC were blended
with a binder (Heraeus V006) to form slurries for both symmetrical cell and single cell fabrication.
The structure of NBSCF-xGDC cathode (x ¼ 0 and 40) were
characterized by using X-ray powder diffraction (XRD) (Rigaku
diffractometer, Cu Ka radiation) with a scan rate of 0.5 min1.
The powder pattern and lattice parameters were analyzed by
Rietveld refinement using GSAS program. In situ XRD of the
NBSCF-xGDC cathode (x ¼ 0 and 40) was obtained from room
temperature to operation temperature (Bruker, D8 Advance).
The microstructures and morphologies of NBSCF-xGDC cathode sample (x ¼ 0, 20, 40, and 50) were observed using a field
emission scanning electron microscope (SEM) (Nova SEM).
To prepare anode supported single cell, NiO powder, GDC
powder, and starch were mixed at weight ratio of 6:4:2 and
ball-milled in ethanol for 24 h. NiO powder and GDC powder
was prepared by glycine nitrate process. The detailed procedure has been described elsewhere [26]. After dried, the NiOGDC mixture was pressed into a pellet which has 0.6 mm
thickness and 15 mm diameter. Thin GDC electrolyte membranes were prepared by a refined particle suspension coating
technique. A GDC suspension was used for the electrolyte
prepared by dispersing GDC powders (Aldrich) in ethanol with
a proper amount of binder (Polyvinyl butyral, B-98) and
dispersant (Triethanolamine, Alfa Aesar) at a ratio of 1:10. The
GDC suspension was applied to a NiO-GDC anode support by
Table 1 e Abbreviation of
NdBa0.5Sr0.5Co1.5Fe0.5O5þdexCe0.9Gd0.1O1.95.
Abbreviation
NBSCF-0GDC
NBSCF-20GDC
NBSCF-40GDC
NBSCF-50GDC
Composition (wt%)
NdBa0.5Sr0.5Co1.5Fe0.5O5þd
Ce0.9Gd0.1O1.95
100
80
60
50
0
20
40
50
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007
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drop-coating, followed by drying in air and subsequent cosintering at 1673 K for 5 h.
Electrochemical impedance spectroscopy of NBSCF-xGDC
(x ¼ 0, 20, 40, and 50) was carried out using a symmetrical cell.
The GDC electrolyte powders were pressed into pellets, and
then sintered at 1623 K for 4 h in air to obtain a dense electrolyte substrate. The slurries were screen-printed onto both
sides of the GDC electrolytes to form symmetrical cells, followed by sintering at 1223 K. The silver wire and silver paste
was used as a current collector for the electrodes. Impedance
spectra were recorded under OCV in a frequency range of
1 mHze500 kHz with AC perturbation of 14 mV from 773 K to
923 K.
Electrochemical performances were evaluated with NiGDC anode supported single cells. To determine the optimized cell performance, NBSCF-xGDC (x ¼ 0 and 40) slurries
were screen-printed on the GDC electrolyte as a cathode. The
cells were finally sintered at 1223 K for 4 h in air with an active
electrode area of 0.36 cm2. The silver wires were used as a
current collector onto both side of the cathode and anode of
single cell using a silver paste. Each cell was mounted on
alumina tube using a ceramic adhesive (Aremco, Ceramabond
553) to fix the single cell. Humidified hydrogen (3% H2O) was
applied as fuel through a water bubbler with a flow rate of
20 mL min1. IeV curves were examined using a BioLogic
Potentiostat at operating temperature from 773 K to 923 K.
The redox properties and oxygen nonstoichiometry of
NBSCF cathode material and NBSCF-40GDC composite were
measured using coulometric titration (CT) as a function of the
oxygen partial pressure, p(O2). A yttria-stabilized zirconia
(YSZ) tube (McDanel Advanced Ceramic Technologies,
Z15410630) was used both to electrochemically pump oxygen
out of the system and to sense the equilibrium in coulometric
titration. The oxygen sensor was part of the container wall
and could also be used to add or remove oxygen from the
system through application of a potential across the ionconducting YSZ tube. The oxide-sample was placed in a
sealed container at the temperature of interest and equilibrated sufficiently by purging 5% O2eAr gas over it in the tube
for 24 h. The detailed procedure has been described elsewhere
[27]. The initial stoichiometric oxygen content of the sample is
determined by iodometric titration and thermogravimetric
analysis (TGA) in air at 973 K [19]. Oxygen partial pressure of
the internal tube was determined from the OCV through the
Nernst equation by the following Equation (1):
4EF
ex
RT
pin
O2 ¼ pO2 $e
(1)
pðOex
2 Þ,
where the
E, F, R, and T stand for the oxygen partial
pressure of the external tube (ca. 0.21 atm), OCV, Faraday
constant, gas constant, and temperature, respectively. The
sample was allowed to equilibrate with the surrounding atmosphere in the tube. Oxygen nonstoichiometry during
coulometric titration is calculated from the Equation (2):
Dd ¼
2M It
V
$Dpin
O2
m 4F RT
(2)
where the M, m, I, t, F, V, R, T, and DpðOin
2 Þ represent for molar
mass of sample, sample mass, applied current, duration time,
Faraday constant, free volume of the tube, gas constant,
Fig. 1 e (a) XRD patterns of pure NBSCF sintered at 1423 K.
(b) Observed, and calculated XRD profiles and the difference
between them for pure NBSCF. (c) XRD patterns of
NBSCFexGDC (x ¼ 0 and 40) mixture after sintering at
1223 K in air.
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007
4
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temperature, and change of oxygen partial pressure of the
internal tube, respectively. The criterion of thermodynamic
equilibrium of oxygen concentration is within 1 mV h1.
Results and discussion
Fig. 1(a) presents XRD patterns of NBSCF sintered at 1423 K for
12 h. The patterns show that NBSCF has a single-phase
layered perovskite structure without any detectable secondary phase. The powder patterns and lattice parameters were
analyzed by Rietveld refinement as described in Fig. 1(b). The
lattice parameters are a ¼ b ¼ 3.858 Å and c ¼ 7.710 Å,
respectively, indicating that NBSCF can be indexed to a
tetragonal structure (space group: P4/mmm) [28]. Under the
actual fuel cell operating conditions, the reaction between the
electrolyte and cathode materials can form an insulating layer
that obstructs the electron and oxygen ion diffusion [29]. In
order to evaluate the chemical compatibility of the
Fig. 2 e (a) In-situ XRD patterns of NBSCF-40GDC sintered at
1223 K, measured at various temperatures, and (b) partially
enlarged in-situ XRD data.
components, XRD measurements were carried out using a
mixture of NBSCF and GDC powders sintered at 1223 K for 4 h.
As shown in Fig. 1(c), there is no solid state reaction between
the NBSCF cathode and the GDC electrolyte, indicating that
the chemical compatibility between NBSCF and GDC is suitable under the present processing condition.
Fig. 2(a) presents in-situ XRD patterns of NBSCF-40GDC
measured from 373 K to 973 K. The XRD patterns indicate
that the NBSCF remains in its layered perovskite structure
over the entire temperature range without any chemical reaction with GDC. Fig. 2(b) shows partially enlarged diffraction
peak of Fig. 2(a). As the temperature increases, the main
diffraction peaks shift to the lower 2 theta, indicating that the
volume of unit cells increases due to the larger size of reduced
B-site cations [30].
Fig. 3 e SEM images show the microstructure of a single
cell (a) the cross-section of NBSCF-40GDC, and the
microstructure of (b) NBSCF-0GDC, (c) NBSCF-20GDC, (d)
NBSCF-40GDC, and (e) NBSCF-50GDC composite cathode.
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 4 ) 1 e7
Fig. 4 e (a) Experimental and fitted impedance spectra of
NBSCF-xGDC symmetrical cells (x ¼ 0, 20, 40, and 50) by the
equivalent circuit shown as an inset, at 873 K. (b)
Comparison of NBSCF-xGDC composite cathode (x ¼ 0, 20,
40, and 50) ASR plotted versus inverse temperatures. (c)
The ASR of symmetrical cells (Rp) measured at 873 K and
fitted R2 and R3 for NBSCF-xGDC (x ¼ 0, 20, 40, and 50)
shown as an inset.
5
The microstructures of the NBSCF-xGDC (x ¼ 0, 20, 40, and
50) cathode are identified by SEM and are presented in Fig. 3
The microstructure of the electrode is related to the characteristics of the surface, the TPB area, volume fraction of
chemical phases, and electron transport [31,32]. The cathode
layer has a highly porous morphology that ensures good oxygen diffusion and its thickness is about 15e20 mm as seen in
Fig. 3(a). The porous NBSCF cathode is adhered well onto the
dense GDC electrolyte (ca. 15 mm) without any cracks or
delamination, which should enhance the mechanical
compatibility. Fig. 3(b) to (e) show the microstructure of the
NBSCF-xGDC (x ¼ 0, 20, 40, and 50) cathode. The small GDC
particles are distributed well over the NBSCF-xGDC composite
cathode (x ¼ 20, 40, and 50) compared to the single-phase
NBSCF cathode, and it is anticipated that this will increase
the electrochemical active sites [22].
The impedance spectra for the symmetrical cells (NBSCFxGDC/GDC/NBSCF-xGDC) were obtained by AC impedance
spectroscopy under various temperatures in air. Fig. 4(a)
shows the representative impedance spectra of NBSCF-xGDC
(x ¼ 0, 20, 40, and 50) composites cathodes at 873 K under an
OCV condition. Electrochemical impedance spectroscopy is
typically used to describe all resistances related with the
electrode and electrolyte of the cell, including the
gasecathode interface, and the cathode-electrolyte interface.
From the spectra, the difference between the intercepts at the
real axis of the Nyquist plots indicates the area specific
resistance (ASR), which is the non-ohmic resistance of the
composite cathode. Arrhenius plots of the cathode non-ohmic
resistances are provided in Fig. 4(b). The ASR of NBSCF-0GDC,
NBSCF-20GDC, NBSCF-40GDC, and NBSCF-50GDC composites
are 0.126, 0.094, 0.074, and 0.082 W cm2, respectively. The ASR
value decreases with increasing GDC ratio up to 40 wt% and
then increases beyond 40 wt% of GDC.
In order to identify the factors of the non-ohmic resistance,
the impedance spectra are fitted by the equivalent circuit.
Fig. 3(c) shows the non-ohmic resistances (Rp) and fitting parameters (R2 and R3) of NBSCF-xGDC (x ¼ 0, 20, 40, and 50)
composites shown as an inset, measured at 873 K under an
OCV condition. The impedance at high and intermediate frequency, R2, is associated with electron, and ion transfer at the
electrode, electrolyte, and interface of the collector and electrode. Meanwhile, the impedance at low frequency, R3, is
related with non-charge transfer, such as oxygen surface exchange and gas-phase diffusion on the electrode layer. With
an increase of the amount of GDC up to 40 wt%, the noncharge transfer resistance (R3) dramatically decreases while
the charge transfer resistance (R2) shows similar values,
indicating that the addition of GDC can improve the rate of
oxygen surface exchange at the interface of MIEC and GDC,
where the ORR occurs. Increasing the amount of GDC beyond
40 wt%, however, leads to a decrease of the electrochemical
performance, because the excessive amount of GDC hinders
the conduction of electrons due to its poor electronic conductivity. Consequently, excessive addition of GDC beyond
40 wt% can impede the ORR, thus indicating that NBSCF40GDC is the most optimized composition for the NBSCF
cathode system.
Fig. 5(a) and (b) show the IeV curve and the corresponding
power density of NBSCF-xGDC/GDC/Ni-GDC (x ¼ 0 and 40)
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007
6
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anode-supported single cells at various temperatures using
humidified H2 (3% H2O) as a fuel and air as an oxidant. As
expected from the lower ASR values of NBSCF-40GDC
compared to those of NBSCF-0GDC, the NBSCF-40GDC single
cell shows excellent cell performance. The maximum power
density of the NBSCF-0GDC and NBSCF-40GDC composite
cathodes was 1.55 and 1.83 W cm2 at 873 K, respectively.
Fig. 6 shows the equilibrium oxygen non-stoichiometries
for bulk NBSCF and the NBSCF-40GDC composite cathode
determined by coulometric titration (CT) as a function of p(O2)
at 973 K. The initial oxygen content of the NBSCF samples are
taken from our previous study [19]. Under actual fuel cell
conditions, the interface of SOFCs between the electrolyte and
the cathode experiences a low p(O2), which may cause redox
degradation of the cathode and affect the long term stability
[23,24]. As can be seen from the data, the NBSCF-0GDC sample
starts to decay at a p(O2) of around ~106 atm, which is
possibly the starting point of decomposition. Meanwhile, the
NBSCF-40GDC composite is stable down to a lower p(O2) of
~107 atm, suggesting that it has superior redox stability
under the operating conditions over the NBSCF bulk cathode
material. Interfacial interactions between NBSCF and GDC
seem to cause the NBSCF to be more reducible. Enhanced
reducibility of the cathode in contact with the electrolyte has
been reported in the previous studies [25,33,34]. The fact that
Fig. 6 e Oxygen non-stoichiometry of NBSCF-xGDC
composite cathode (x ¼ 0 and 40) as a function of p(O2) at
973 K.
the electrode in contact with the electrolyte material, i.e.,
composite cathode, can endure more reduced state may
indicate that addition of GDC on NBSCF cathode improve the
oxygen redox stability, although a definitive explanation is
obviously not yet available. Therefore, specific addition of
GDC on a bulk NBSCF cathode can be a relevant process for
enhancement of oxygen redox stability.
Conclusions
The electrochemical properties of NBSCF-xGDC cathode materials were systematically investigated to optimize the GDC
ratio based on the structural characteristics, the electrochemical performance, and the redox stability of the cathode
for IT-SOFC application. The favorable electrochemical properties of NBSCF-xGDC composites originate from an electrocatalytic effect stemming from the provision of additional
electrochemically active sites where the electrochemical reaction occurs. Accordingly, the optimized NBSCF-40GDC
cathode material had the lowest ASR, 0.074 W cm2 at 873 K,
resulting in remarkable cell performance of 1.83 W cm2 at
873 K. In addition, the oxygen redox stability is an important
factor that influences the stability of cathode materials. The
isotherms of NBSCF-40GDC obtained from a coulometric
titration experiment reveal higher redox stability at lower
p(O2). This study demonstrates that optimized addition of GDC
on the NBSCF cathode not only improves the electrochemical
performance but also enhances the oxygen redox stability.
Acknowledgments
Fig. 5 e IeV curves and corresponding power density
curves of single cells (NBSCF-xGDC/GDC/Ni-GDC) under
various temperatures; (a) x ¼ 0 and (b) x ¼ 40.
This research was supported by the Mid-career Researcher
Program (2013R1A2A2A04015706) and funded by the Ministry
of Science, ICT and Future Planning, and the BK21 Plus
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 4 ) 1 e7
Program (META-material-based Energy Harvest and Storage
Technologies, 10Z20130011057) and the Basic Science
Research Program (2010-0021214) funded by the Ministry of
Education (MOE, Korea) and National Research Foundation of
Korea (NRF).
references
[1] Park S, Vohs JM, Gorte RJ. Direct oxidation of hydrocarbons in
a solid-oxide fuel cell. Nature 2000;404:265e7.
[2] Shao Z, Haile SM, Ahn J, Ronney PD, Zhan Z, Barnett SA. A
thermally self-sustained micro solid-oxide fuel-cell stack
with high power density. Nature 2005;435:795e8.
[3] Jacobson AJ. Materials for solid oxide fuel cells. Chem Mater
2010;22:660e74.
[4] Steele BCH, Heinzel A. Materials for fuel-cell technologies.
Nature 2001;414:345e52.
[5] Shao Z, Haile SM. A high-performance cathode for the next
generation of solid-oxide fuel cells. Nature 2004;431:170e3.
[6] Ishihara T, Fukui S, Nishiguchi H, Takita Y. La-Doped BaCoO3
as a cathode for intermediate temperature solid oxide fuel
cells using a LaGaO3 base electrolyte. J Electrochem Soc
2002;149:A823e8.
[7] Yoo S, Lim T-H, Shin J, Kim G. Comparative characterization
of thermodynamic, electrical, and electrochemical
properties of Sm0.5Sr0.5Co1xNbxO3d (x ¼ 0, 0.05, and 0.1) as
cathode materials in intermediate temperature solid oxide
fuel cells. J Power Sources 2013;226:1e7.
[8] Jun A, Yoo S, Gwon O-H, Shin J, Kim G. Thermodynamic and
electrical properties of Ba0.5Sr0.5Co0.8Fe0.2O3d and
La0.6Sr0.4Co0.2Fe0.8O3d for intermediate-temperature solid
oxide fuel cells. Electrochim Acta 2013;89:372e6.
[9] Park S, Choi S, Shin J, Kim G. Electrochemical investigation of
strontium doping effect on high performance Pr1xSrxCoO3d
(x ¼ 0.1, 0.3, 0.5, and 0.7) cathode for intermediate-temperature
solid oxide fuel cells. J Power Sources 2012;210:172e7.
[10] Kim J-H, Manthiram A. LnBaCo2O5þd oxides as cathodes for
intermediate-temperature solid oxide fuel cells. J
Electrochem Soc 2008;155:B385e90.
n A, Parfitt D, Kilner JA. Oxygen
[11] Chroneos A, Yildiz B, Taranco
diffusion in solid oxide fuel cell cathode and electrolyte
materials: mechanistic insights from atomistic simulations.
Energy Environ Sci 2011;4:2774e89.
[12] Kim G, Wang S, Jacobson AJ, Reimus L, Brodersen P,
Mims CA. Rapid oxygen ion diffusion and surface exchange
kinetics in PrBaCo2O5þx with a perovskite related structure
and ordered A cations. J Mater Chem 2007;17:2500e5.
[13] Kim YN, Kim J-H, Manthiram A. Effect of Fe substitution on
the structure and properties of LnBaCo2xFexO5þd (Ln ¼ Nd
and Gd) cathodes. J Power Sources 2010;195:6411e9.
[14] Yoo S, Shin JY, Kim G. Thermodynamic and electrical
properties of layered perovskite NdBaCo2xFexO5þdeYSZ
(x ¼ 0, 1) composites for intermediate temperature SOFC
cathodes. J Electrochem Soc 2011;158:B632e8.
[15] Kim J-H, Prado F, Manthiram A. Characterization of
GdBa1xSrxCo2O5þd (0 x 1.0) double perovskites as
cathodes for solid oxide fuel cells. J Electrochem Soc
2008;155:B1023e8.
[16] Park S, Choi S, Kim J, Shin J, Kim G. Strontium doping effect
on high-performance PrBa1xSrxCo2O5þd as a cathode
material for IT-SOFCs. ECS Electrochem Lett 2012;1:F29e32.
7
[17] Kim JH, Cassidy M, Irvine JTS, Bae J. Advanced
electrochemical properties of LnBa0.5Sr0.5Co2O5þd (Ln ¼ Pr,
Sm, and Gd) as cathode materials for IT-SOFC. J Electrochem
Soc 2009;156:B682e9.
[18] Jun A, Kim J, Shin J, Kim G. Optimization of Sr content in
layered SmBa1xSrxCo2O5þd perovskite cathodes for
intermediate-temperature solid oxide fuel cells. Int J
Hydrogen Energy 2012;37:18381e8.
[19] Choi S, Yoo S, Kim J, Park S, Jun A, Sengodan S, et al. Highly
efficient and robust cathode materials for low-temperature
solid oxide fuel cells: PrBa0.5Sr0.5Co2xFexO5þd. Sci Rep
2013;3:2426e31.
[20] Dyck CR, Yu ZB, Krstic VD. Thermal expansion matching of
Gd1-xSrxCoO3-d composite cathodes to Ce0.8Gd0.2O1.95 IT-SOFC
electrolytes. Solid State Ionics 2004;171:17e23.
[21] Leng Y, Chan SW, Liu Q. Development of LSCFeGDC
composite cathodes for low-temperature solid oxide fuel
cells with thin film GDC electrolyte. Int J Hydrogen Energy
2008;33:3808e17.
[22] Kim J, Seo W-Y, Shin J, Liu M, Kim G. Composite cathodes
composed of NdBa0.5Sr0.5Co2O5þd and Ce0.9Gd0.1O1.95 for
intermediate-temperature solid oxide fuel cells. J Mater
Chem A 2013;1:515e9.
[23] Adler SB. Factors governing oxygen reduction in solid oxide
fuel cell cathodes. Chem Rev 2004;104:4791e843.
[24] Bastidas DM, Tao S, Irvine JTS. A symmetrical solid oxide fuel
cell demonstrating redox stable perovskite electrodes. J
Mater Chem 2006;16:1603e5.
[25] Kim G, Vohs JM, Gorte RJ. Enhanced reducibility of ceriaeYSZ
composites in solid oxide electrodes. J Mater Chem
2008;18:2386e90.
[26] Jun A, Shin J, Kim G. High redox and performance stability of
layered SmBa0.5Sr0.5Co1.5Cu0.5O5þd perovskite cathodes for
intermediate-temperature solid oxide fuel cells. Phys Chem
Chem Phys 2013;15:19906e12.
[27] Yoo S, Shin JY, Kim G. Thermodynamic and electrical
characteristics of NdBaCo2O5þd at various oxidation and
reduction states. J Mater Chem 2011;21:439e43.
[28] Maignan A, Martin C, Pelloquin D, Nguyen N, Raveau B.
Structural and magnetic studies of ordered oxygen-deficient
perovskites LnBaCo2O5þd, closely related to the “112”
structure. J Solid State Chem 1999;260:247e60.
[29] Rossignol C, Ralph JM, Bae J-M, Vaughey JT. Ln1xSrxCoO3
(Ln ¼ Gd, Pr) as a cathode for intermediate-temperature solid
oxide fuel cells. Solid State Ionics 2004;175:59e61.
[30] Nakayama M, Ikuta H, Uchimoto Y, Wakihara M. Ionic
conduction of lithium in B-site substituted perovskite
compounds, (Li0.1La0.3)yMxNb1xO3 (M ¼ Zr, Ti, Ta). J Mater
Chem 2002;12:1500e4.
n B. Review on modeling
[31] Andersson M, Yuan J, Sunde
development for multiscale chemical reactions coupled
transport phenomena in solid oxide fuel cells. Appl Energy
2010;87:1461e76.
[32] Nam JH, Jeon DH. A comprehensive micro-scale model for
transport and reaction in intermediate temperature solid
oxide fuel cells. Electrochim Acta 2006;51:3446e60.
[33] Costa-Nunes O, Ferrizz R, Gorte RJ, Vohs JM. Structure and
thermal stability of ceria films supported on YSZ(1 0 0) and aAl2O3(0 0 0 1). Surf Sci 2005;592:8e17.
[34] Costa-Nunes O, Gorte RJ, Vohs JM. High mobility of ceria
films on zirconia at moderate temperatures. J Mater Chem
2005;15:1520e2.
Please cite this article in press as: Kim C, et al., Effects of composite cathode on electrochemical and redox properties for intermediate-temperature solid oxide fuel cells, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/
j.ijhydene.2014.07.007