Electrode properties of (Pr0.9La0.1)2?x(Ni0.74Cu0.21Al0.05)O4+δ (with x=0, 0.05, and 0.1)as cathodes in IT-SOFCs

Article abstract of DOI:10.1016/j.jallcom.2019.04.078

A Ruddlesden-Popper phase, (Pr_0.9La_0.1)_2?x(Ni_0.74Cu_0.21Al_0.05)O_4+δ ((PL)_2?xNCA, x = 0, 0.05 and 0.1), is synthesized and characterized for use as a cathode material in intermediate temperature solid oxide fuel cells (IT-SOFCs). The effects of A-site cation deficiency on the thermal expansion coefficient, electrical conductivity, electrochemical properties, and thermal stability are investigated in detail. (PL)_2?xNCA and the Ce_0.8Sm_0.2O_1.9 (SDC)electrolyte are chemically compatible at 1000 °C for 5 h. The average thermal expansion coefficient (TEC)values of (PL)_2?xNCA range from 14.1 × 10^?6 K^?1 to 14.5 × 10^?6 K^?1 for temperatures between 30 and 1000 °C, which is close to that of conventional SOFC electrolyte materials. The (PL)_2?xNCA samples were unstable after heating to 700 and 800 °C for 72 h in air. The (PL)_1.9NCA cathode had a minimum area specific resistance (ASR)of 0.033 Ω cm² at 800 °C. When (PL)_2.0NCA was used as the cathode material in electrolyte-supported single cells, the single cell reached a maximum power density of 527 mW cm^?2 at 800 °C using an SDC electrolyte.

Full text of DOI:10.1016/j.jallcom.2019.04.078

Accepted Manuscript
Electrode properties of (Pr La (with x=0, 0.05,
)
(Ni
Cu
Al
)O
0
.9 0.1 2−x 0.74 0.21 0.05 4+δ
and 0.1) as cathodes in IT-SOFCs
Jialun Mao, Shuting Peng, Chao Zhang, Jinghao Cui, Runze Shao, Yuhan Gong,
Shaoshuai Wang, Chongrui Wu, Qingjun Zhou
PII:
S0925-8388(19)31344-1
DOI:
https://doi.org/10.1016/j.jallcom.2019.04.078
JALCOM 50262
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 8 January 2019
Revised Date: 5 April 2019
Accepted Date: 7 April 2019
Please cite this article as: J. Mao, S. Peng, C. Zhang, J. Cui, R. Shao, Y. Gong, S. Wang, C. Wu, Q.
Zhou, Electrode properties of (Pr La (with x=0, 0.05, and 0.1)
)
(Ni
Cu
Al
)O
0
.9 0.1 2−x 0.74 0.21 0.05 4+δ
as cathodes in IT-SOFCs, Journal of Alloys and Compounds (2019), doi: https://doi.org/10.1016/
j.jallcom.2019.04.078.
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ACCEPTED MANUSCRIPT
Electrode Properties of (Pr La ) (Ni Cu Al )O
0
.9
0.1 2−x
0.74
0.21
0.05
4+δ
(with x=0, 0.05, and 0.1) as Cathodes in IT-SOFCs
Jialun Mao, Shuting Peng, Chao Zhang, Jinghao Cui, Runze Shao, Yuhan Gong, Shaoshuai Wang,
Chongrui Wu, Qingjun Zhou∗
College of Science, Civil Aviation University of China, Tianjin 300300, PR China.
Abstract
A Ruddlesden-Popper phase, (Pr La ) (Ni0.74Cu0.21Al0.05)O4+δ ((PL) NCA,
0
.9
0.1 2−x
2−x
x=0, 0.05 and 0.1), is synthesized and characterized for use as a cathode material in
intermediate temperature solid oxide fuel cells (IT-SOFCs). The effects of A-site
cation deficiency on the thermal expansion coefficient, electrical conductivity,
electrochemical properties, and thermal stability are investigated in detail.
(
PL) NCA and the Ce Sm O (SDC) electrolyte are chemically compatible at
2−x 0.8 0.2 1.9
1
000 °C for 5 h. The average thermal expansion coefficient (TEC) values of
−
6
−1
−6
−1
(
PL) NCA range from 14.1×10 K to 14.5×10 K for temperatures between 30
2−x
and 1000 °C, which is close to that of conventional SOFC electrolyte materials. The
PL) NCA samples were unstable after heating to 700 and 800 °C for 72 h in air.
(
2
−x
The (PL) NCA cathode had a minimum area specific resistance (ASR) of 0.033 ꢀ
1
.9
2
cm at 800 °C. When (PL) NCA was used as the cathode material in
2
.0
electrolyte-supported single cells, the single cell reached a maximum power density of
−2
5
27 mW cm at 800 °C using an SDC electrolyte.
Keywords: Solid oxide fuel cells; Cobalt-free cathode; K NiF -type oxide; A-site
2
4
deficiency
∗
Corresponding author. Fax: 86-022-24092514; E-mail addresses: qjzhousofc@163.com (Q.
Zhou), qjzhou@cauc.edu.cn
1

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1
. Introduction
Solid oxide fuel cells (SOFCs) are a promising energy conversion technology that
can directly convert chemical energy stored in a variety of fuels to electricity with low
high efficiency and low pollutant emissions [1,2]. Traditional SOFCs usually work at
high temperatures (800∼1000 °C) and are highly efficient. However, high operating
temperatures lead to many serious problems, including interface reactions, thermal
expansion mismatch between the cell components, limited long-term durability, and
high material costs. Consequently, extensive efforts have been devoted to the
development of intermediate temperature (IT) (600∼800 °C) SOFCs. However, a
decrease in the operating temperature usually leads to a quick increase in the cathode
polarization resistance. Therefore, it is essential to develop alternative cathode
materials that have high electrochemical activities for oxygen reduction reactions
(ORRs) for use in IT-SOFCs. Some mixed ionic–electronic conducting oxides have
been widely investigated for use as cathode materials in IT-SOFCs due to their good
catalytic activities for ORRs [3−8].
Recently, K NiF -type oxides have become attractive structures for use as
2
4
alternative cathode materials in SOFCs, demonstrating very good thermal expansion
compatibilities with electrolytes and superior electrochemical performance [9−21].
Most research has concentrated on Ln NiO (Ln = lanthanide). It is well known that
2
4
Ln NiO can accommodate interstitial oxygen in its LnO rock-salt layers and
2
4
3
+
compensate for the formation of Ni holes by forming Ni [22,23]. In addition, fast
oxygen diffusivity is observed along the rock-salt layer, i.e., conduction along the
ab–axis [24−26]. The electrical conductivity of Ln NiO is p-type and reached nearly
2
4
−1
1
00 S cm at 800 °C under high oxygen partial pressures [27]. The thermal
expansion of Ln NiO is generally lower than that of the commonly used
2
4
perovskite-type cathodes [14, 27], which are compatible with the most commonly
used electrolyte materials, such as yttria-stabilized zirconia (YSZ), Ce Sm O
0
.8
0.2 2−δ
(
SDC) and La Sr Ga Mg O (LSGM).
0.9 0.1 0.8 0.2 3−δ
Yashima et al. found that (Pr La ) (Ni0.74Cu0.21Ga0.05)O4+δ (PLNCG) has a
0
.9
0.1 2
2

ACCEPTED MANUSCRIPT
relatively high oxygen permeation rate and good structural stability [28,29]. Wang
et al. investigated the stability of PLNCG under a CO atmosphere, and the results
2
indicated that PLNCG possesses excellent long-term stability under the
CO -containing atmosphere [30,31]. Very recently, Xue et al. reported the
2
development of an A-site cation deficient (Pr La ) (Ni0.74Cu0.21Ga0.05)O4+δ
0
.9
0.1 1.9
2
hollow-fiber membrane with a permeation flux of 2.51 mL/min cm at 975 °C under
an air/He gradient [32]. In addition, Yang et al. reported the use of PLNCG as an
SOFC cathode, which greatly improved the electrochemical performance. An
extremely low ASR was observed for PLNCG at 800 °C [33]. Our previous study
showed that the cathode performance of (Nd La ) (Ni0.74Cu0.21Al0.05)O4+δ (NLNCA)
0
.9
0.1 2
is better than that of La NiO [34,35] and Pr Ni Cu O [36]. Moreover, Al-doped
2
4+δ
2
0.6
0.4
4
NLNCA possessed similar cathode properties to Ga-doped PLNCG under the same
conditions [33,34]. It is well known that Pr NiO4+δ is the most electrochemically
2
active of the K NiF -type compounds when it is used in IT-SOFCs. However,
2
4
Pr NiO
has demonstrated low thermodynamic stability under the working
2
4+δ
conditions of SOFCs. Additionally, because Al is clearly much cheaper than Ga,
Al-doped (Pr La ) (Ni0.74Cu0.21Al0.05)O4+δ (PLNCA) should be investigated as a
0
.9
0.1 2
potential
cathode
material
for
IT-SOFCs.
For these reasons,
(
Pr La ) (Ni0.74Cu0.21Al0.05)O4+δ ((PL) NCA, x=0, 0.05 and 0.1) was prepared to
0
.9
0.1 2−x
2−x
investigate the effect of A-site cation deficiency on the properties of PLNCA,
including electrical conductivity, chemical compatibility with the Sm Ce O (SDC)
0
.2
0.8 1.9
electrolyte, thermal properties, and electrochemical performance, as well as the
structural stability in oxygen-containing atmospheres.
2
. Experimental
2
.1 Synthesis of powders
The (PL) NCA (x=0, 0.05 and 0.1) materials, (PL) NCA, (PL)1.95NCA, and
2
−x
2.0
(
PL) NCA, were prepared by the combined EDTA-citrate complexing sol-gel
1.9
process, as previously reported [34]. Ni(NO ) ·3H O (98.5%), Cu(NO ) ·3H O
3
2
2
3 2
2
(
99.0-102.0%), and Al(NO ) ·9H O (99.99%) were used as the starting materials.
3 3 2
3

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Stoichiometric amounts of high-purity Pr O (99.9%) and La O (99.99%) were
6
11
2
3
dissolved in nitric acid to form nitrates. Stoichiometric amounts of the nitrates were
then dissolved in deionized water and mixed to prepare a metal precursor solution.
EDTA (99.5%) and citric acid (99.8%) were then added to the solution at a molar
ratio of 1: 1: 2 (total metal ions: EDTA: citric acid). The pH of the aqueous solution
was adjusted to approximately 6 to prevent the formation of a precipitate. A
homogeneous black viscous gel was obtained under stirring and heating. The gel was
transferred to an oven and heat-treated at 200 °C for 5 h to obtain a primary powder
and further calcined at 1000 °C for 5 h to obtain a pure-phase Ruddlesden-Popper
oxide. The glycine–nitrate process was used to prepare the Sm Ce O (SDC)
0
.2
0.8 1.9
electrolyte and NiO anode powders, as described elsewhere [37].
.2 Preparation of symmetrical and single fuel cells
Symmetrical cells with the (PL) NCA/SDC/(PL) NCA configuration were
2
2
−x
2−x
fabricated for electrochemical impedance spectroscopy (EIS) measurements. That is,
a (PL) NCA slurry was coated onto both sides of the SDC electrolyte pellet by a
2
−x
screen-printing method. After drying, the (PL) NCA cathode was sintered in air at
2
−x
1
000 °C for 2 h. A diluted silver paste was used as the current collector. An
electrolyte supported single-cell was fabricated using SDC electrolyte pellets with
thicknesses of ∼300 µm. The NiO−SDC (65:35 wt.%) anode ink was screen-printed
on the surface of the SDC electrolyte and co-fired at 1250 °C for 4 h. Subsequently,
the (PL) NCA cathode ink was screen-printed on the opposite side of the SDC pellet
2
−x
and sintered at 1000 °C for 2 h to form a single cell. The single cell was sealed on an
alumina supported tube by applying the diluted silver paste.
2
.3 Basic characterization
X-ray diffraction (XRD) was performed for phase identification of the
(
PL) NCA powders using a Rigaku D/Max RA diffractometer with Cu Kα radiation.
2−x
o
o
The XRD patterns were recorded in the 2θ range from 20 to 80 with intervals of
0
.02°.
Thermogravimetric analysis (TGA) was performed on an SDT Q600 (V20.9 Build
2
0) instrument. The sample was put into an alumina crucible and heated in air with a
4

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flow rate of 100 mL/min and a heating rate of 10 °C/min.
For the electrical conductivity and TEC measurements, the (PL) NCA powders
2
−x
were uniaxially pressed into pellets and bars and then sintered at 1100 °C in air for 10
h. The electrical conductivity was measured via the van der Pauw method at a
temperature range from 100 to 850 °C in ambient air. The thermal expansion data
were collected using a Netzsch DIL 402 Expedis Classic dilatometer in air at a
temperature range from 30 to 1000 °C with a ramp rate of 5 °C /min.
EIS was performed on (PL) NCA using an electrochemical workstation (Zahner
2
−x
IM6ex frequency analyzer) at temperatures ranging from 600 to 800 °C at 50 °C
intervals in ambient air. EIS spectra were collected at frequencies ranging from 100
kHz to 100 mHz, and the signal amplitude was 10 mV. The I-V and I-P polarization
curves were collected using an electrochemical analyzer (Ivium Technologies) in the
four-probe mode. High-purity hydrogen was fed into the anode side of the fuel cell,
while the cathode side was exposed to ambient air.
The microstructure was observed using a Nova NanoSEM 230 field emission
scanning electron microscope (FE-SEM, FEI, Netherlands). The long-term phase
stabilities of the (PL) NCA samples were determined by long-term phase stability
2
−x
measurements, which involves heating the powders in alumina crucibles at 600, 700,
and 800 °C for 72 h in an air atmosphere. The resulting powders were characterized
by XRD.
3
. Results and discussion
3
.1 Crystal structure and chemical compatibility
Fig. 1 shows the room-temperature XRD pattern of (PL) NCA after calcination at
2
−x
1
000 °C in air for 5 h. As shown in Fig. 1(a), all three materials adopt the
K NiF -type structure, and no impurity phases were observed. In addition, it is
2
4+δ
important to evaluate the chemical compatibility between the cathode and the
electrolyte, which may affect the cell performance. The chemical compatibility of the
(
PL) NCA sample with the SDC electrolyte was assessed by heating the mixture at
2−x
1
000 °C for 5 h in air. As shown in Fig. 1(b), no new peaks were detected. It appears
5

ACCEPTED MANUSCRIPT
that (PL) NCA is chemically compatible with the SDC electrolyte.
2
−x
3
.2 Thermal analysis
The thermal evolution of the synthesized (PL) NCA powders was studied by
2
−x
recording TGA curves in air. Fig. 2 compares the TGA curves of the (PL) NCA
2
−x
powders with temperature. The three curves show a similar trend for temperature
between 30 and 1000 °C. The weight loss that occurs below ~350 °C is likely due to
the desorption of physically adsorbed water and carbon dioxide. The weight of the
materials with x =0, 0.05 and 0.1 starts to decrease after the temperature reaches
~
350 °C, which is primarily associated with the thermal reduction of Ni and Cu ions
and the corresponding release of interstitial oxygen. The weight losses are 0.66% for
PL) NCA, 0.55% for (PL) NCA, and 0.51% for (PL) NCA, which implies that
(
2
.0
1.95
1.9
many more interstitial oxygens are released in the non A-site cation deficient
PL) NCA sample with increasing temperature than the other samples. Two
(
2
.0
possibilities are considered in this case; one possibility is that A-site cation vacancies
and oxygen vacancies are formed by introducing an A-site cation deficiency, while
the other possibility is that charge neutrality is maintained by the reduction of
interstitial oxygen.
3
.3 Thermal expansion behavior
For practical applications of SOFCs, the fuel cell components should have similar
TEC values, which is required for obtaining sufficient thermo-mechanical
compatibility. The TECs of the (PL) NCA samples were measured in air, and the
2
−x
results are shown in Fig. 3. No abrupt changes appeared in the thermal expansion
curves of (PL) NCA in the measured temperature range. The average TECs of the
2
−x
−
6
−1
(
PL) NCA samples measured from 30 to 1000 °C are 14.5×10 K for (PL) NCA,
2−x 2.0
−
6
−1
−6 −1
1
4.2 ×10 K for (PL) NCA, and 14.1×10 K for (PL) NCA, which is much
1.95 1.9
−
6
−1
closer to that of the SDC (11.4×10 K ) electrolyte material [34]. Additionally, the
TECs are significantly lower compared to the commonly used Co- and Fe-based
−
6
−1
perovskites, such as BaBi0.05Co Nb0.15O3–δ (20.7×10
K ) [38] and
0.8
−
6
−1
Sm1.875Ba3.125Fe O (17.2×10 K ) [39].
5
15–δ
3
.4. Electrical conductivity
6

ACCEPTED MANUSCRIPT
Fig. 4 shows the temperature-dependent electrical conductivity (σ) for (PL) NCA.
2
−x
A similar trend has been observed in the (PL) NCA electrical conductivity results.
2
−x
With increasing temperature, the electrical conductivity first increased and then
decreased by further increasing the temperature to over 450 °C. The decrease in
electrical conductivity observed in this temperature range may be due to the loss of
lattice oxygen and the formation of oxygen vacancies. The loss of lattice oxygen
results in a decrease in the charge carrier concentration and/or the annihilation of
partial electronic holes, as indicated in Eq. (1):
1
×
o
•
••
o
O + 2h = V + O (g)
(1)
2
2
×
•
••
where Oo is the lattice oxygen,
h
is the electron hole and Vo is
the
oxygen
vacancy. As shown in Fig. 4(a), the electrical conductivity decreases with increasing
A-site cation deficiency content (increasing the x value from 0.0 to 0.1). The
−
1
maximum electrical conductivity of (PL) NCA is 77 S cm , which is much larger
2
.0
−1
−1
than that of (PL)1.95NCA (63 S cm ) and (PL) NCA (57 S cm ). Based on
1.9
the principles of defect chemistry and electroneutrality, the introduction of an A-site
cation deficiency into (PL) NCA should promote the formation of additional
2
.0
2
+
2+
3+
3+
oxygen vacancies and/or the oxidation of Ni /Cu
to Ni /Cu .
The conductivity decreases with increasing A-site cation deficiencies, and therefore,
the charge compensation mechanism induced by the A-site cation deficiency in
(
PL) NCA is mainly caused by the formation of oxygen vacancies and not by the
2−x
oxidation of B-site cations to higher valence states. This trend is consistent with other
A-site cation deficient cathodes, such as (La Sr ) Co Fe O ,
0
.6 0.4 1−x
0.2 0.8 3−δ
(
Ba Sr ) Co Fe O , and Pr BaCo O [40−42]. The relationship between
0.5 0.5 1−x 0.8 0.2 3−δ 1−x 2 5+δ
ln(σT) and 1000/T in the Arrhenius plots are shown in Fig. 4(b); the linear
relationship can be observed at low temperatures. A small polaron conduction
mechanism can account for this conduction. The activation energy (Ea) values
calculated from the slope of the fitted line are 0.110, 0.111, and 0.099 eV for
(
PL) NCA, (PL) NCA, and (PL) NCA, respectively. A lower Ea indicates a
2.0 1.95 1.9
higher catalytic activity for the oxygen reduction reaction (ORR). A slight decrease in
7

ACCEPTED MANUSCRIPT
the Ea value of the (PL) NCA sample compared to (PL) NCA and (PL)1.95NCA
1
.9
2.0
indicates that a larger A-site cation deficiency might improve the catalytic activity of
the oxygen reduction reaction (ORR).
3
.5. Area specific resistance
To examine the effects of the A-site cation deficiency on the cathode electrochemical
properties, EIS spectra for the symmetrical cell were obtained at different
temperatures in air. The Nyquist plots for (PL) NCA from 600−800 °C are shown in
2
−x
Fig. 5(a) − (c). For comparison, all bulk resistances are normalized to zero. The
difference between the real axis intercepts of the impedance arc is the cathode area
specific resistance (ASR). The ASRs of (PL) NCA in the temperature range of
2
−x
6
00–800 °C are shown in Table 1. The ASR values of (PL) NCA when x = 0, 0.05,
2−x
2
and 0.1 are 0.037, 0.036 and 0.033 ꢀ cm at 800 °C, respectively. The (PL) NCA
2
.0
cathode has a much lower ASR compared to the (PL)1.95NCA and (PL) NCA
1.9
cathodes at low temperatures (600−700 °C). However, the ASR values of (PL) NCA,
2
.0
(
PL)1.95NCA and (PL) NCA are almost the same for temperatures from 750−800 °C.
1.9
As discussed in the electrical conductivity section, (PL) NCA has a higher
2
.0
conductivity and is more favorable for charge transfer in the electrode, while the
introduction of an A-site cation deficiency into (PL) NCA may lead to the creation
2
.0
of more oxygen vacancies at relatively high temperatures. The formation of oxygen
vacancies on the electrode can provide active sites for the ORR. The
preliminary results indicate that, for (PL) NCA, a better balance between the
2
−x
conductivity and the oxygen vacancy concentration (catalytic activity) is achieved
throughout the temperature range of 600−800 °C. In addition, the ORR activity of
(
PL) NCA is found to also be much higher than that of some common Co-based
2−x
2
cathodes reported by various groups, such as LaSrCoO (ASR = 0.385 ꢀ cm at
4
2
8
50 °C) [43], YBaCo Ga O
(ASR = 0.111 ꢀ cm at 800 °C) [44],
3
.2
0.8 7+δ
2
La Sr Co Fe O (ASR =0.44 ꢀ cm at 690 °C) [45] and SrCo Ta O (ASR
0
.6 0.4
0.2 0.8
3
0.9
0.1 3−δ
2
=
0.054 ꢀ cm at 800 °C) [46]. In terms of the ASR values, the (PL) NCA (x = 0,
2−x
0
.05, and 0.1) cathodes have excellent electrocatalytic activities for ORRs at
intermediate temperatures.
8

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3
.6. Single-cell performance
The electrochemical performances of the (PL) NCA cathodes were further
2
−x
evaluated in single cells with the electrolyte-supported configuration of
NiO-SDC/SDC/(PL) NCA. Fig. 6 shows the cell power density and cell potential as
2
−x
a function of the current density, using pure hydrogen as the fuel and ambient air as
the oxidant in a temperature range of 600−800 °C. The peak power densities of the
single cells with the (PL) NCA, (PL) NCA and (PL) NCA cathodes at 800 °C are
2
.0
1.95
1.9
−
2
5
27, 485, and 477 mW cm , respectively. Not surprisingly, the x = 0.0 composition
has the best cell performance, which is consistent with the higher electrical
conductivity and lower ASR observed in (PL) NCA. Although there is a slight
2
.0
decrease in the power output with increasing A-site cation deficiencies in (PL) NCA,
2
−x
all (PL) NCA samples offer substantially high electrochemical performances, over
2
−x
−2
4
50 mW cm , and as a result, they are promising cathode materials for IT-SOFC
applications.
Fig. 7 show the cross-sectional SEM images of the (PL) NCA/ SDC/NiO–SDC
2
.0
electrolyte supported single cell and the (PL) NCA/SDC interface after cell testing.
2
.0
As presented in Fig. 7(a), the thicknesses of the SDC electrolyte, NiO–SDC anode
and (PL) NCA cathode are estimated to be approximately 300, 16 and 30 µm,
2
.0
respectively. As seen in Fig. 7(b), the (PL) NCA cathode has good adhesion with the
2
.0
SDC electrolyte, suggesting a good thermal compatibility between the cathode and
SDC at high temperatures. Additionally, the cathode layer has a porous morphology,
and the particle-size distribution is uniform.
3
.7 Phase stability
The long-term phase stabilities of all the single-phase (PL) NCA (x = 0.0, 0.05,
2
−x
and 0.1) samples were assessed by heating at 600, 700, and 800 °C for 72 h under an
air atmosphere and followed by quenching to room temperature. The long-term phase
stability XRD patterns are shown in Fig. 8. The XRD patterns indicate that the
(
PL) NCA samples are stable at 600 °C after a 72 h exposure (Fig. 8(a)), while the
2−x
samples show significant phase decomposition at for exposures at 700 and 800 °C for
2 h. The XRD patterns show that (PL) NCA is decomposed into PrNiO (or
7
2
−x
3
9

ACCEPTED MANUSCRIPT
LaNiO ), Pr O , Pr NiO , and NiO at 700 °C (Fig. 8(b)), while at 800 °C, the
3
6
11
2
4
decomposed products would be PrNiO (or LaNiO ), Pr O , and Pr CuO (Fig. 8(c)).
3
3
6
11
2
4
Therefore, to further improve the stability of the (PL) NCA cathode, it is necessary
2
−x
to suppress phase decomposition, either by A-site or B-site substitutions at elevated
temperatures between 700 and 800 °C.
4
. Conclusions
In this work, (PL) NCA (x=0, 0.05 and 0.1) with K NiF -type oxides have been
2
−x
2
4
investigated for use as cathode materials in IT-SOFCs. All prepared (PL) NCA
2
−x
samples show good chemical compatibility with the SDC electrolyte after sintering at
000 °C for 5 h. The electrical conductivity decreases with increasing A-site cation
1
deficiencies due to the decreased charge carrier concentration. The introduction of
A-site cation deficiencies has no significant effect on the TEC. A small A-site cation
deficiency does not obviously improve the electrochemical performance of the
(
PL) NCA cathode. The (PL) NCA samples have good ORR catalytic activities;
2−x 2−x
2
2
the ASRs of (PL) NCA, (PL) NCA and (PL) NCA are 0.046 ꢀ cm , 0.048 ꢀ cm
2
.0
1.95
1.9
2
and 0.050 ꢀ cm at 750 °C in air, respectively. The peak power densities of the single
cells with (PL) NCA, (PL) NCA and (PL) NCA as the cathodes reached 527,
2
.0
1.95
1.9
−2
4
85, and 477 mW cm at 800 °C, respectively. Unfortunately, (PL) NCA suffers
2−x
from phase decomposition at high temperatures. Therefore, further work should focus
on improving the phase stability of (PL) NCA at high temperatures.
2
−x
Acknowledgements
The research was financially supported by the Fundamental Research Funds for the
Central Universities (3122017083), the National Undergraduate Training Programs
for Innovation and Entrepreneurship (201710059007), the Tianjin Research Program
of Application Foundation and Advanced Technology (15JCYBJC48700) and the
Scientific Research Project of Tianjin Education Committee (2018KJ254).
References
[
[
1] N.Q. Minh, J. Am. Ceram. Soc. 76 (1993) 563–588.
2] S. Park, J.M. Vohs, R.J. Gorte, Nature 404 (2000) 265–267.
1
0

ACCEPTED MANUSCRIPT
[
[
[
3] Z.P. Shao, S.M. Haile, Nature 431 (2004) 170–173.
4] Q.J. Zhou, T.M. He, Q. He, Y. Ji, Electrochem. Commun. 11 (2008) 80–83.
5] H.Y. Tu, Y. Takeda, N. Imanishi, O. Yamamoto, Solid State Ionics 117 (1999)
2
77–281.
6] Q.J. Zhou, L. Xu, Y.J. Guo, D. Jia, Y. Li, W.C.J. Wei, Int. J. Hydrogen Energy 37
2012) 11963–11968.
[
(
[
7] W. Zhou, J. Sunarso, M. W. Zhao, F. L. Liang, T. Klande, A. Feldhoff, Angew.
Chem., Int. Ed. 52 (2013) 14036–14040.
[
[
[
8]Y. Cheng, Q.J. Zhou, L.B. Chen, Y.T. Xie, Mater. Lett. 193 (2017) 105–107.
9] R. Sayers, J. Liu, B. Rustumji, S.J. Skinner, Fuel Cells 8 (2008) 338–343.
10] D. Pérez-Coll, A. Aguadero, M.J. Escudero, P. Núñez, L. Daza, J. Power Sources
1
78 (2008) 151–162.
[
11] C. Ferchaud, J.-C. Grenier, Y. Zhang-Steenwinkel, M.M.A. van Tuel, F.P.F. van
Berkel, J-M. Bassat, J. Power Sources 196 (2011)1872–1879.
[
[
12] J. Wan, J.B. Goodenough, J.H. Zhu, Solid State Ionics 178 (2007) 281–286.
13] M. Ferkhi, A. Ringuedé, A. Khaled, L. Zerroual, M. Cassir, Electrochim Acta 75
(
2012) 80–87.
14] C.Zhao, Q.J. Zhou,T. Zhang, L.W. Qu, X. Yang,T. Wei, Mater. Res. Bull. 113
2019) 25–30.
15] M.B. Bansod, A.P. Khandale, R.V. Kumar, S.S. Bhoga, Int. J. Hydrogen Energy
3 (2018) 373–384.
[
[
(
4
[
[
16] S.L. Li, H.Y. Tu, F. Li, M.T. Anwar, L.J. Yu, J. Alloys Compd. 694 (2017)17–23.
17] L. Sun, Q. Li, H. Zhao, L.H. Huo, J.C. Grenier, J. Power Sources 183 (2008)
43–48.
[
18] S. Nishimoto, S. Takahashi, Y. Kameshima, M. Matsuda, M. Miyake, J. Ceram.
Soc. Jpn. 119 (2011) 246–250.
[
[
19] M.J. Escudero, A. Fuerte, L. Daza, J. Power Sources 196 (2011) 7245–7250.
20] A. Aguadero, J.A. Alonso, M.J. Escudero, L. Daza, Solid State Ionics 179 (2008)
393–400.
[
21] Y. Shen, H. Zhao, X. Liu, N. Xu, Phys. Chem. Chem. Phys. 12 (2010)
11

ACCEPTED MANUSCRIPT
1
5124–15131.
22] J. Jorgensen, B. Dabrowski, S. Pei, D. Richards, D. Hinks, Phys. Rev. B 40 (1989)
187–2199.
[
2
[
[
23] A. Mehta, P.J. Heaney, Phys. Rev. B 49 (1994) 563–571.
24] A.R. Cleave, J.A. Kilner, S.J. Skinner, S.T. Murphy, R.W. Grimes, Solid State
Ionics 179 (2008) 823–826.
[
[
[
[
[
[
[
[
[
[
[
[
25] A. Chroneos, D. Parfitt, J.A. Kilner, R.W. Grimes, J. Mater. Chem. 20 (2010)
2
66–270.
26] D. Parfitt, A. Chroneos, J.A. Kilner, R.W. Grimes, Phys. Chem. Chem. Phys. 12
2010) 6834–6836.
(
27] M. Al Daroukh, V.V. Vashook, H. Ullmann, F. Tietz, I. Arual Raj, Solid State
Ionics 158 (2003) 141–150.
28] M. Yashima, N. Sirikanda, T. Ishihara, J. Am. Chem. Soc. 132 (2010)
2385–2392.
29] M. Yashima, M. Enoki, T. Wakita, R. Ali, Y. Matsushita, F. Izumi, T. Ishihara,
J. Am. Chem. Soc. 130 (2008) 2762–2763.
30] J. Tang, Y.Y. Wei, L.Y. Zhou, Z. Li, H.H. Wang, AIChE J. 58 (2012)
2
473–2478.
31] Y.Y. Wei, J. Tang, L.Y. Zhou, J. Xue, Z. Li, H.H. Wang, AIChE J. 58 (2012)
856–2864.
32] Q. Liao, L.B. Zhuang, Y.Y. Wei, J. Xue, H.H. Wang, Ceram. Int. 44 (2018)
0852–10857.
2
1
33] Y.X. Wang, X.Y. Zhao, S.Q. Lü, B. Yu, X.W. Meng, Y.J. Zhang, J.H.
Yang, C.W. Fu, Y. Ji, Ceram. Int. 40 (2014) 7321–7321.
34] Q.J. Zhou, Y. Gao, F. Wang, D.M. An, Y. Li, Y.L. Zou, Z.P. Li, W.B. Wang,
Ceram. Int. 41 (2015) 639–643.
35] K. Zhao, Q. Xu, D.P. Huang, W. Chen, M. Chen, B.H. Kim, J. Solid State
Electrochem 16 (2012) 9–16.
36] Y.F. Wang, J.G. Cheng, Q.M. Jiang, J.F. Yang, J.F. Gao, J. Power Sources 196
(2011) 3104–3108.
1
2

ACCEPTED MANUSCRIPT
[
[
37] Y. Cheng, Q.J. Zhou, W.D. Li, T. Wei, Z.P. Li, D.M. An, X.Q. Tong, Z.H. Ji, X.
Han, J. Alloys Compd. 641 (2015) 234–237.
38] Q.J. Zhou, T. Wei, Z.P. Li, D.M. An, X.Q. Tong, Z.H. Ji, W.B. Wang, H. Lu, L.Y.
Sun, Z.Y. Zhang, K. Xu, J. Alloys Compd. 627 (2015) 320–323.
[
[
[
39] Q.J. Zhou, L.B. Chen, Y. Cheng, Y.T. Xie, Ceram. Int. 42 (2016) 10469–10471.
40] G.Ch. Kostogloudis, Ch. Ftikos, Solid State Ionics 126 (1999) 143–151.
41] W. Zhou, R. Ran, Z.P. Shao, W.Q. Jin, N.P. Xu, J. Power Sources 182 (2008)
24–31.
[
[
[
42] L.L. Zhang, G.B. Yao, Z.Y. Song, B.B. Niu, W. Long, L. Zhang, Y. Shen, T.M. He,
Electrochim Acta 212 (2016) 522–534.
43] Y. Hu, Y. Bouffanais, L. Almar, A. Morata, A. Tarancon, G. Dezanneau, Int. J.
Hydrogen Energy 38 (2013) 3064–3072.
44] Q.J. Zhou, Y. Shi, T. Wei, Z.P. Li, D.M .An, J.W. Hu, W.H. Zhao, W. Zhang,
Z.H. Ji, J.H. Wang, Int. J. Hydrogen Energy 39 (2014) 10710–10717.
45] E.P. Murray, M.J. Sever, S.A. Barnett, Solid State Ionics 148 (2002) 27–34.
46] Q.J Zhou, T. Wei, Y.H. Shi, S.Q. Guo, Y. Li, J.X. Su, H. Ren, Y. Zhu,
Curr. Appl. Phys. 12 (2012) 1092–1095.
[
[
Figures captions
Fig. 1. (a) Room-temperature XRD patterns of the as-synthesized (PL) NCA (x = 0,
2
−x
0
.05, and 0.10) samples and (b) chemical compatibility of the (PL) NCA samples
2−x
with the SDC electrolyte.
Fig. 2. TGA curves for (PL) NCA (x = 0, 0.05, and 0.10) as a function of
2
−x
temperature in air.
Fig. 3. Thermal expansion ꢀL/L curves of (PL) NCA (x = 0, 0.05, and 0.10)
0
2−x
measured between 30 and 1000 °C in air.
Fig. 4. Temperature dependence of the electrical conductivity of the (PL) NCA (x =
2
−x
0
, 0.05, and 0.10) samples: (a) electrical conductivity vs. temperature and (b) Ln (σT)
vs. 1000/T.
Fig. 5. Electrochemical impedance spectra of the (PL) NCA (x = 0, 0.05, and 0.10)
2
−x
1
3

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cathodes in contact with the SDC electrolyte at various temperatures in air.
Fig. 6. Performances of the Ni−SDC/SDC/(PL) NCA single cells at various
2
−x
temperatures: (a) x = 0.0, (b) x= 0.05, and (c) x = 0.1.
Fig. 7. SEM micrograph of (a) the (PL) NCA/SDC/NiO–SDC cross-section and (b)
2
.0
the (PL) NCA/SDC cross-section after testing.
2
.0
Fig. 8. XRD patterns of the (PL) NCA (x = 0, 0.05, and 0.10) sample powders after
2
−x
the 72 h long-term phase stability tests at 600, 700 and 800 °C.
2
Table 1. ASR (ꢀ cm ) values of the (PL) NCA samples at 600−800 °C for
2
−x
symmetrical cells (PL) NCA/SDC/(PL) NCA.
2
−x
2−x
650 °C
0.182
0.234
0.235
Temperature (°C)
600 °C
0.519
0.766
0.727
700° C
0.082
0.101
0.100
750 °C
0.046
0.048
0.050
800 °C
0.037
0.036
0.033
(
(
(
PL) NCA
2.0
PL)1.95NCA
PL) NCA
1
.9
1
4

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Highlights
1
. The system (Pr La ) (Ni0.74Cu0.21Al0.05)O4+δ ((PL) NCA) evaluated as
0
.9
0.1 2−x
2−x
candidate cathode materials for IT-SOFCs.
. (PL) NCA has a good chemical compatibility with SDC electrolyte.
2
3
4
5
2
−x
. The TECs of (PL) NCA was much lower than cobalt-based cathodes.
2
−x
2
. Low ASR of 0.033 ꢀ cm was obtained with (PL) NCA at 800 °C.
1
.9
. (PL) NCA suffers from phase decomposition at high temperatures.
2
−x