An Efficient Electron-Blocking Interlayer Induced by Metal Ion Diffusion

Subscriber access provided by UNIV OF SCIENCES PHILADELPHIA

Article

An Efficient Electron-Blocking Interlayer Induced by Metal Ionic Diffusion for SOFC Based on Y-doped Ceria Electrolyte Jiafeng Cao, Yi Liu, Xianshan Huang, and Yuexia Ji ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b18924 • Publication Date (Web): 01 Mar 2018 Downloaded from http://pubs.acs.org on March 4, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

An Efficient Electron-Blocking Interlayer Induced by Metal Ionic Diffusion for SOFC Based on Y-doped Ceria Electrolyte Jiafeng Cao, Yi Liu, Xianshan Huang, and Yuexia Ji* School of Mathematics and Physics, Anhui University of Technology, Maanshan, 243032, PR China ABSTRACT: To suppress the internal electronic leakage at ceria-based electrolyte, a novel electron-blocking layer consisting of doped BaCe0.8Y0.2O3-δ was fabricated in situ at the interface of Ba-containing anode and Y-doped ceria electrolyte. The anode-supported full cell based on Y0.2Ce0.8O1.9 (YDC20) electrolyte presents a remarkable peak power density of 814 mW/cm2 as well as an open circuit voltage (OCV) of 1.0 V at 650 °C, which are much higher than those of the cells with Gd0.1Ce0.9O1.95 (GDC10) electrolyte (453 mW/cm2 at 650 °C) and BaCe0.8Y0.2O3-δ|Y0.2Ce0.8O1.9 (BCY|YDC20) bi-layered electrolyte (419 mW/cm2 at 650 °C), respectively. The efficient promotion of the electron-blocking interlayer with high oxygen ionic conductivity is considered as the main reason for the improved performance of YDC20-based SOFC. The composition and the microstructure of the electron-blocking interlayer are further analyzed by SEM and TEM characterizations. KEYWORDS: solid oxide fuel cells, internal electronic leakage, Y-doped ceria, electron-blocking layer, in-situ reaction the cell performance. Recently, the in-situ fabrication of an

1. INTRODUCTION

electron-blocking layer between anode and electrolyte Solid oxide fuel cell (SOFC) has been regarded as one of the most efficient and fuel flexible energy conversion devices

1-4

through Ba ions diffusion was reported and considered as an

.

efficient approach in suppressing the internal electronic 16, 17

Reducing the operating temperature (below 700 °C) of SOFC

leakage at ceria-based electrolytes

is an urgent issue to develop low-temperature solid oxide

the cell can sufficiently insulate the ceria electrolyte from the

fuel cell (LT-SOFC) which can reduce the system cost, de-

reducing fuel and thus block off the internal electronic short

crease the performance degradation rate and substantially

circuit. Our previous research reported that a novel Ba-

increase the lifetime of SOFC

5-7

. The new structure in

. Doped ceria (DCO) is a

containing anode 0.6NiO-0.4BaZr0.45Ce0.45Gd0.1O3-δ (NiO-

widely used solid electrolyte in the research of LT-SOFC.

BZCG) was used to fabricate a thin electron-blocking inter-

Gd

3+

and Sm

3+

doped ceria are the most popular electrolytes

layer in situ at the interface of anode and Gd0.1Ce0.9O1.95

in the development of LT-SOFCs for their higher ionic conductivities than the other rare-earth ions doped ceria

(GDC10) electrolyte

8, 9

18

. The new functional interlayer can

.

efficiently reduce the n-type electronic conductivity at

However, the partial internal electronic short circuit induced

GDC10 causing enhanced open cell voltages (OCVs). Howev-

by the reduction of Ce

4+

3+

to Ce

under reducing atmosphere

er, the performance of the cell supported by NiO-BZCG is

remains a significant challenge for the applications of ceria-

inferior to most traditional ceria-based SOFCs. The function-

based electrolytes in LT-SOFC devices

10, 11

.

al interlayer can be considered as the main factor limiting

In order to eliminate the internal electronic short circuit

the cell performance under working conditions. Therefore,

through electrolytes mentioned above, many attempts have

improving the electron-blocking layer is an urgent issue to

been reported such as depositing Y0.1Zr0.9O2-δ (YSZ) doped bismuth oxide

14, 15

12, 13

or

develop new strategy of eliminating the internal electronic

on ceria electrolyte membrane.

short circuit at ceria-based electrolytes and to study the

However, YSZ seems not to be a very proper choice consider-

working mechanism of the interlayer.

ing its low ionic conductivity. Meanwhile, the partial internal

Until now, the research about the controllable design of

short circuit still existed in the cell implanted by a doped

the electron-blocking layer has not been frequently reported

bismuth oxide layer demonstrating limited improvement of

and not attracted sufficient attention. Therefore, the control-

A ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 11

lable construction of the interlayer between anode and elec-

ed onto the electrolytic side and co-sintered at 950 °C for 3 h

trolyte is valuable and important to the development of ce-

in air to form full cell. To investigate the micro-structural

ria-based SOFCs with high performance. In this research, 20

characteristics of the diffusion layer at the interface of anode

mol% Y-doped ceria was employed as the electrolyte in order

and electrolyte, the sample from the diffusion layer was ob-

to achieve the fabrication of doped BaCe0.8Y0.2O3-δ electron-

tained through a co-firing process with YDC20 sintered be-

blocking interlayer under high temperature sintering. The

tween two pressed NiO-BZCG pellets at 1350 °C for 5 h.

micro-morphology of this novel interlayer was characterized.

XRD patterns of the powders were analyzed by an X-ray

The improvement of this functional layer to the performance

diffractometer (Rigaku TTR-III) in the range of 20-80°. Mi-

of DCO-based SOFCs was further analysed.

crostructures of the samples were observed with a scanning electron microscope (SEM, JSM-6700F) and a high-resolution

2. EXPERIMENTAL

transmission electron microscopy (TEM, JEM-2100F). Cells In this work, the samples for anode, electrolyte and cathode

testing measurements were performed using 3% H2O humid-

were synthesized in one step by a citric acid-nitrate gel com-

ified hydrogen as fuel at a flow rate of 20 mL min and the

bustion process according to previous reports

−1

cathode was exposed to atmospheric air in a cell testing sys-

18, 19

. C4H6BaO4

(99 % purity), Zr(NO3)4·5H2O (99 % purity), Ce(NO3)3·6H2O

tem with the temperature changing from 650 to 500 °C. Sil-

(99 % purity), Gd2O3 (99.95 % purity) and Ni(NO3)2·6H2O

ver paste was applied as a current collector over the cathodes

(98 % purity) raw materials from Sinopharm were used in

and silver wires were used as the conducting wires for fuel

the synthesis of 0.6NiO-0.4BaZr0.45Ce0.45Gd0.1O3-δ (NiO-BZCG)

cells test. I-V curves of the cells were measured with a DC

powder (NiO-BZCG, weight ratio 6:4). Stoichiometric afore-

electronic load (ITech electronics model IT8511) based on the

mentioned raw powders were first dissolved in diluted nitric

two-probe configuration. The electrochemical impedance

acid. Citric acid was used as a complexing agent, and the

spectra (EIS) were obtained under open circuit conditions by

molar ratio of citric acid and metal ions at anode powder was

a CHI604E impedance analyzer for the frequency dependent

1.5. NH4OH was used to adjust the pH value at 7. The solu-

observation from 100 kHz to 0.1 Hz. The polarization re-

tion was under the conditions of pH 7 and stationary com-

sistances of the cells under open circuit conditions were de-

plexation for at least 8 h. Then the solution was continuously

termined from the recorded EIS results.

heated under stirring until ignited to a flame and then

3. RESULTS AND DISCUSSIONS

burned off to be a black ash. The ash was then transferred into a furnace annealed at 1050 °C for 5 h to obtain pure NiO-

Figure 1 provides the XRD spectra of the as-prepared pow-

BZCG anode powder. 20 wt % starch was added into NiO-

ders for the fabrication of full cells. It is clear that through

BZCG composite by sufficient ball milling for 24 h to form

combustion preparations, well-crystallized samples with

porosity at anode. Y0.2Ce0.8O1.9 (YDC20) was employed as the

sharp diffraction peaks can be obtained. The diffraction

electrolyte and also synthesized by the same method with a

peaks of the electrolyte powder are well matched with the

calcining process at 600 °C for 5 h. For comparison, the cell

cubic phase of YDC20 (PDF No.75-0175 ), while the spectra of

with Gd0.1Ce0.9O1.95 (GDC10) electrolyte and BaCe0.8Y0.2O3-

anode and cathode powders correspond to the phases of pure

δ|Y0.2Ce0.8O1.9

NiO-BZCG and SSC-SDC without any impurity indicating

(BCY|YDC20) bi-layered electrolyte were also

successful syntheses of the aimed powders in this work.

studied in this issue. The electrolyte ash for comparison and Sm0.5Sr0.5CoO3-δ and Ce0.8Sm0.2O3-δ (SSC and SDC) cathode ash were also synthesized by the same method. After combustion, the as-prepared GDC10 and BCY powders were heated at 600 °C for 5 h and 1000 °C for 3 h, respectively, to obtain pure phase. The SSC and SDC powders were mixed in a weight ratio of 7:3 and mixed thoroughly together with a 6 wt. % ethylcellulose-terpineol binder to prepare the cathode slurry. Anode-supported half-cell was obtained by a copressing process with the same amount of electrolyte powder (the weight ratio of BCY/YDC20 is 1:2 for the bi-layered electrolyte) and co-fired at 1350 °C for 5 h to obtain half-cell on YDC20, GDC10 or BCY|YDC20 electrolytes of high density. Subsequently, SSC-SDC composite cathode slurry was paint-

B ACS Paragon Plus Environment

Page 3 of 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. XRD patterns of NiO-BZCG, YDC20 and SSC-SDC powders.

Figure 2. SEM image of the electrolytic surface of NiOBZCG|YDC20 half-cell after sintering at 1350 °C-5h. SEM detection was used to investigate the morphology and particle size of the YDC20 electrolyte sintered at 1350 °C for 5 h. As is presented in Figure 2, the YDC20 electrolyte

Figure 3. SEM picture of the cross section of NiO-

with particles diameters in the range of 1-5 μm possesses a

BZCG|YDC20|SSC-SDC full cell.

smooth surface and high density without any pore, which is important to the sufficient separation of fuel and oxygen and beneficial for the energy conversion efficiency and stability of the cell. The

morphology

of

the

cross

section

of

NiO-

BZCG|YDC20|SSC-SDC full cell was investigated and shown in Figure 3. Both the anode and cathode display a porous morphology and tightly attach on the facet of dense YDC20 electrolyte. It is clear that this porous construction is beneficial for the transport of the fuel, the oxygen and the reaction products of the cell under working conditions. SEM observation coupled with EDS analysis was conducted to determine the elements distribution at NiOBZCG|YDC20 interface. A SEM-EDS analysis of a representative interface of the sample is shown in Figure 4. The different position of Ba (red curve) and Ni (green curve) peak edges along the interface can be regarded as an obvious illus-

Figure 4. SEM-EDS analysis of the interface between NiO-

tration of the metal ionic diffusion. Focussing on this inter-

BZCG and YDC20 membrane for the half-cell sintered at

face, the peak edge of Ba singal can be found extending to

1350 °C for 5 h.

the right side of Ni singal, which demonstrates that Ba ions have obviously diffused into the electrolyte in a miro-meter scale (3.6 μm) forming a functional layer at anode|electrolyte interface.

C ACS Paragon Plus Environment


Page 4 of 11

2

814, 632 and 449 mW/cm at 650, 600 and 550 °C, while the NiO-BZCG|GDC10|SSC-SDC cell only exhibits MPDs of 453, 2

300 and 156 mW/cm as the temperature decreasing from 650 to 550 °C (Figure 5 (b)). According to the above-tested OCVs and power densities results, the electrolytes and the interlayers in the cells are the main reasons for the different performances under the same conditions. As is widely known to us, GDC10 electrolyte displays much higher oxygen ionic conductivity than that of YDC20

20, 21

, and GDC10 is common-

ly employed as the electrolytic candidate in ceria-based SOFCs. Thus, the superior power densities output for YDC20-based cell can be finally attributed to the different functional interlayer formed between NiO-BZCG anode and YDC20 electrolyte compared with the SOFC based on GDC10. In addition, it can be seen in Figure 5 (a) that the OCVs of the cell on the bi-layered electrolyte are relatively lower than those of the cell on YDC20 electrolyte. And the MPD values of NiO-BZCG|YDC20|SSC-SDC cell are much superior to NiO-BZCG|BCY|YDC20|SSC-SDC cell (419, 331 and 227 2

mW/cm as the temperature ranging from 650 to 550 °C ), demonstrating the advantage of the in-situ fabrication in synthesizing thin electron-blocking interlayer between anode and electrolyte.

Figure 5. (a) I-V and I-P curves of NiO-BZCG|YDC20|SSCSDC full cell, (b) NiO-BZCG|GDC10|SSC-SDC

18

and (c) NiO-

BZCG|BCY|YDC20|SSC-SDC at the same temperature range. Figure 5 displays the plots of cell voltage and power density versus current density for NiO-BZCG|YDC20|SSC-SDC, NiO-BZCG|GDC10|SSC-SDC

and

NiO-

BZCG|BCY|YDC20|SSC-SDC full cells. All of the as-prepared cells show higher OCVs compared with the cell supported by NiO-GDC anode (about 0.8 V)

18

at the whole temperature

range. In Figure 5 (a), the OCVs of the full cell with YDC20 electrolyte are observed to be 1.0 V, 1.011 V and 1.02 V at 650, 600 and 550 °C, respectively, which are much higher than those of the ceria-based SOFCs with traditional anodes

16, 18

.

The improved OCVs can be attributed to the sufficient suppression of internal short circuit at YDC20 electrolyte. The maximum power densities (MPDs) of the cells with different electrolytes plotted in Figure 5 (a), (b) and (c) exhibit obvious difference under the same testing temperature. For the NiO-BZCG|YDC20|SSC-SDC cell (Figure 5 (a)), the MPDs are

D ACS Paragon Plus Environment

Page 5 of 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. OCVs and power densities (PDs) of recent typical DCO-based SOFCs with or without electron-blocking layers.

Anodes

Electrolytes

Cathodes

OCVs (V)

MPDs

PDs (mW cm-2

(mW cm-2)

/0.9 V)

Ref.

NiO-GDC

GDC10 (3 μm)

LSCF

0.86 (600 °C)

992 (600 °C)

0 (600 °C)

22

NiO-GDC

GDC10 (20 μm)

SSC-GDC

0.787 (650 °C)

694 (650 °C)

0 (650 °C)

23

NiO-SDC

SDC15 (20 μm)

BSCF

0.87 (600 °C)

1010 (600 °C)

0 (600 °C)

2

NiO-SDC

SDC20 (18 μm)

SSC-SDC

0.849 (650 °C)

1011 (650 °C)

0 (650 °C)

9

NiO-BZCYYb

SDC (30 μm)

LSCF

1.029 (650 °C)

640 (650 °C)

200 (650 °C)

17

NiO-BZY

SDC20 (15 μm)

SSC-SDC

1.037 (650 °C)

638 (650 °C)

239 (650 °C)

24

NiO-BZCG

GDC10 (20 μm)

SSC-SDC

1.012 (650 °C)

453 (650 °C)

101 (650 °C)

18

SSC-SDC

1.04 (650 °C)

267 (650 °C)

～80 (650 °C)

25

SSC-SDC

1.0 (650 °C)

814 (650 °C)

206 (650 °C)

BaZr0.1Ce0.7Y0.2O3δ(11

NiO-SDC

μm)|Ce0.8Sm0.2 O2-δ (19 μm)

NiO-BZCG

YDC20 (17 μm)

This work

work.). The thick BaZr0.1Ce0.7Y0.2O3-δ layer (11 μm) and the Table 1 lists some common DCO-based SOFCs with or

insufficient contact surface between BaZr0.1Ce0.7Y0.2O3-δ and

without electron-blocking layers. Compared with NiO-SDC

Ce0.8Sm0.2O2-δ are the main limiting factors that are disadvan-

and NiO-GDC anodes, Ba-containing anodes generally in-

tageous for the enhancement of the cell performance.

duce an obvious increase in OCV value of the full cell. Tradi-

Through the in-situ fabrication in this work, the electron-

tionally, Gd or Sm dopants are commonly used in the re-

blocking layer can be formed in a micrometer scale (as

search of ceria-based electrolytes. It is notable that the prop-

shown in Figure 4) while the interface can be effectively im-

erty of the cell with 20 mol% Y-doped ceria electrolyte in this

proved resulting in the enhanced MPDs.

work can be seen comparable with or even higher than many cells based on GDC or SDC electrolytes. Besides, the im-

Figure 6 presents the electrochemical impedance spectra

proved cell in this research shows a relatively large power

(EIS) of the cells on YDC20, GDC10 and BCY|YDC20 mem-

density of 206 mW cm with a high working voltage of 0.9 V

branes measured from 650 to 550 °C under open circuit con-

while the cells with NiO-GDC or NiO-SDC anodes can hardly

ditions. The plots of these cells with different electrolytes can

output any power density under the same voltage. Thus, it is

be simulated according to the equivalent circuit in the insets,

notable that Y-doped ceria electrolyte may be more suitable

which will be discussed in the following section. The high-

in the ceria-based cell supported by Ba-containing anodes

frequency intercept of EIS corresponds to the ohmic re-

-2

compared with the cells based on GDC or SDC electrolytes.

sistance (Ro) mainly representing the electrolyte resistance.

Furthermore, the MPDs in this work are much higher than

The low-frequency intercept corresponds to the total re-

those of the fuel cell based on bi-layered BaZr0.1Ce0.7Y0.2O3-δ(11

sistance of the cell. The difference between the high frequen-

μm)|Ce0.8Sm0.2O2-δ(19 μm) electrolyte evaluated for the elim-

cy and low frequency intercepts with the real axis is the total

ination of internal short circuit at SDC with the peak power

interfacial polarization resistance (Rp) of the cell, which is mainly contributed by the microstructure of the electrodes

-2

densities of only 267, 197, and 127 mW cm at 650, 600, and . (The BaZr0.1Ce0.7Y0.2O3-δ in the cell

and the electrode|electrolyte interfaces. Accordingly, the

coupled with bi-layered BaZr0.1Ce0.7Y0.2O3-δ|Ce0.8Sm0.2O2-δ

improved cell in this work display much higher Rp values

electrolyte that works as an electron-blocking layer possesses

than those of the cells without Ba-containing anodes

a similar composition with the electron-blocking layer in this

measuring temperature points resulting from the formation

550 °C, respectively

25

19

at the

of an electron-blocking interlayer. These results are well con-

B ACS Paragon Plus Environment


sistent with the previous researches

Page 6 of 11

26, 27

: the high Rp values

of the improved cells can be ascribed to the in-situ fabrication of the functional interlayer which suppresses the leaking current through the electrolyte film and generally reduces the electrode reactions.

-2

Figure 7. Power density curve (mW cm ) as a function of time (h) for NiO-BZCG|YDC20|SSC-SDC full cell operating at 600 °C under a working voltage of 0.7 V. To characterize the stability of NiO-BZCG|YDC20|SSCSDC cell, the power density during long-term testing under H2/air operation at a constant voltage of 0.7 V at 600 °C was obtained, as is provided in Figure 7. The power density of the improved cell remains extremely stable during the testing course of 50 hours, which can be attributed to the good thermal expansion compatibility and chemical stability of the electron-blocking layer in the cell induced by the diffusion of metal ions including Ba, Ni, Zr, Gd and so on. As is wildly known to us, barium cerate that can react with H2O forming hydroxides is unstable with pH2O of 1 atm even below 400 °C 28, 29

. Commonly, Zr-doped barium cerate display high im-

provement of the chemical stability in the presence of water or CO2 vapor

Figure 6. (a) Impedance spectra plots of the cell on YDC20

30-32

. The enhanced stability of the electron-

blocking layer demonstrated that Zr ions sufficiently partici-

membrane. (b) EIS results of NiO-BZCG|GDC10|SSC-SDC

pate in the in-situ reaction at the interface increasing the

cell and (c) EIS plots of the cell on BCY|YDC20 bi-layered

stability of the full cell. (It can be seen in Figure S1 and S2

membrane. All of the above cells were measured under open

that the electron-blocking interlayer possesses a high Zr con-

circuit conditions from 650 to 550 °C.

centration, which will be discussed in the following part.) These results show that the functional diffusion layer formed between NiO-BZCG and YDC20 is beneficial for the improvement of the stability of SOFC. In order to determine the chemical composition of the functional interlayer, the YDC20 fired between two NiOBZCY pellets was observed by a high-resolution TEM. Figure S1 shows the TEM results in line-scan mode. It is obviously seen that strong signals of Ba, Ce and Y elements can be detected. Besides, Zr, Ni and Gd signals can also be observed and the distributions of these elements can be found uniform without obvious segregation. TEM surface scan of the sample was also carried out and shown in Figure S2. The results in

F ACS Paragon Plus Environment

Page 7 of 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure S2 are well consistent with the TEM line-scan analyses,

the electrolyte to react with the fuel at anode. And the resis-

illustrating the same uniform distributions of the above ions

tance to oxygen ions diffusion through the interlayer is an

and no obvious segregation. Accordingly, the metal ions dis-

important factor that can not be negligible. Therefore, the

tributions in that electron-blocking interlayer are uniform,

equivalent circuit model

probably forming a new compound with a single phase.

6, should be used in this work considering the resistance to

33

, as is seen in the insets of Figure

To characterize the phase of the electron-blocking layer,

oxygen ions diffusion through the inter-diffusion layer. The

high-resolution TEM analysis of the as-prepared grain from

resistance to oxygen ions diffusion of the interlayer can be

the interlayer was obtained, as is shown in Figure 8. It can be

represented by a finite diffusion Warburg impedance Zw. R0

seen that the high resolution image is highly consistent with

represents the ohmic resistance of bulk electrolyte, the oh-

the PDF card: No.82-2372 with the interplanar crystal spacing

mic contact resistance at anode and cathode sides. R1 and R2

of 0.31 nm for (002) lattice plane, which can be typically iden-

are anodic polarization resistance and cathodic polarization

tified as a doped BaCeO3 oxide. Thus, the functional interlay-

resistance (Ω cm ), respectively. C1 and C2 represent the

er in this work can be confirmed as a new BaCeO3-based

double layer capacitances at anode side (F cm ) and the

2

2

2

oxide with perovskite structure induced by the in-situ reac-

double layer capacitances at cathode side (F cm ). Figure S3

tion between different diffused metal ions. Due to the pres-

provides

ence of the chemical composition gradient at the interface of

BZCG|YDC20|SSC-SDC cell based on the aforementioned

NiO-BZCG anode and YDC20 electrolyte, the metal ions (Ba,

equivalent circuit model (Figure 6). As clearly seen in Figure

Zr, Ni and Gd) at anode can inevitably diffuse into the elec-

S3 (a), (b) and (c), the simulated impedance data fit well with

trolyte under high temperature sintering. According to the

the measured impedance data at the operating temperatures

elements intensities in Figure S1, the in-situ reaction between

from 650 to 550 °C. Subsequently, the impedance fitted re-

Ba

sults

ions and YDC20

can

induce

the

formation

of

the

of

impedance

fitting

results

NiO-BZCG|GDC10|SSC-SDC

of

NiO-

and

NiO-

BaCe0.8Y0.2O3-δ oxide. Other metal ions, Zr, Ni and Gd also

BZCG|BCY|YDC20|SSC-SDC were also obtained based on the

participate in the in-situ reaction probably working as metal

same equivalent circuit model, as shown in Figure S4 and S5.

dopants. Thus, it can be deduced that Zr, Ni, Gd co-doped

All of the simulated results fit well with the measured impe-

BaCe0.8Y0.2O3-δ can be fabricated at the interface of NiO-

dance data except the result in Figure S5 (a), in which the

BZCG and YDC20.

fitted spots deviate more from the actual data due to the insufficient points from the EIS records for NiO-BZCG| BCY|YDC20|SSC-SDC cell induced by the partial decomposition of BCY under water vapor-containing atmospheres which will inevitablly result in recording discrete points at low frequencies

34, 35

. From the fitted results in Figure S3, S4 2

and S5, one interesting comparison of the Zw(R) (Ω cm ) values demonstrate a reasonable evolution trend for the oxygen ionic conduction abilities of the different interlayers between anode and electrolyte. For NiO-BZCG|YDC20|SSC-SDC full cell, the values of Zw(R) are simulated to be 0.0473 Ω, 0.2492 2

Ω and 0.6086 Ω cm from 650 to 550 °C, while the corresponding values of the full cells based on GDC10 electrolytes are 2

simulated to be 0.474, 0.9721 and 1.905 Ω cm , respectively. In addition, the Zw(R) values of the cell on BCY|YDC20 bi2

layered electrolyte are 0.3137, 0.8912 and 1.733 Ω cm from 650 to 550 °C, respectively. Clearly, the cell with the in-situ fabrication of doped BaCe0.8Y0.2O3-δ electron-blocking interFigure 8. High-resolution TEM image of the grain in the elec-

layer displays higher oxygen ionic conductivity than those of

tron-blocking layer.

the cells with GDC10 or BCY|YDC20 electrolytes, which is beneficial for the oxygen ions diffusion through the inter-

Considering the interlayer with perovskite structure

layer and the improvement of cell performance.

formed between anode and electrolyte, the oxygen ions should diffuse through the interlayer after they transfer from

G ACS Paragon Plus Environment


Page 8 of 11

BaCe0.8Y0.2O3-δ oxide can be formed in situ at the interface of anode and electrolyte. Commonly, doped BaCe0.8Y0.2O3-δ oxide is a mixed proton and oxide ion conductor under fuel cell conditions

36, 37

. The doped BaCe0.8Y0.2O3-δ oxide in the inter-

layer works as an oxide ionic conductor while suppresses the electronic conduction through the electrolyte. The total conductivity of the interlayer can remarkably affect the performance of the full cell. Previous researches have provided that 20 mol% Y doped BaCeO3 or BaCeO3-BaZrO3-based electrolytes demonstrated higher conductivities than those of the electrolytes with 10 mol% Gd doped BaCeO3-BaZrO3-based oxides

36, 37

. It can be deduced that Zr, Ni, Gd co-doped

BaCe0.8Y0.2O3-δ oxide presents a higher conductivity than that of Zr, Ni co-doped BaCe0.9Gd0.1O3-δ oxide. Therefore, the internal electronic leakage at Y-doped ceria electrolyte can be efficiently suppressed while the total conductivity of the interlayer still maintains in a high level. Due to the higher conductivity of the improved interlayer, the cell based on YDC20 electrolyte demonstrated higher MPDs than those of the cell with GDC10 electrolyte.

4. CONCLUSIONS To eliminate the internal electronic leakage at ceria-based electrolyte and to improve the conductivity of the functional Figure 9. (a) The illumination of electronic conduction

interlayer, NiO-BZCG anode-supported cell based on YDC20

through NiO-YDC|YDC20 interface. (b) The mechanism of

electrolyte was fabricated. The corresponding results showed

the in-situ reaction induced by metal ionic diffusion at the

that the cell with YDC20 electrolyte exhibited higher perfor-

interface between NiO-BZCG and GDC10. (c) The mecha-

mances than those of the cell based on GDC10 and

nism of the in-situ reaction at the interface of NiO-BZCG and

BCY|YDC20 bi-layered electrolyte. The main reason can be

YDC20. (d) Schematic representation of the electronic and

probably attributed to the different interlayer formed be-

oxygen ionic conduction at the interface under working con-

tween anode and electrolyte under high temperature sinter-

ditions.

ing. Zr, Ni, Gd co-doped BaCe0.8Y0.2O3-δ interlayer between

Figure 9 shows the schematic illustrations of the cells with

NiO-BZCG and YDC20 demonstrated a higher total conduc-

different anodes and electrolytes. For the cell composed of

tivity than that of Zr, Ni co-doped BaCe0.9Gd0.1O3-δ (between

NiO-YDC20 anode and YDC20 electrolyte, the electrolyte

NiO-BZCG and GDC10) and BCY interlayer fabricated by

exposed to the reducing atmosphere inevitably exists the

direct co-pressing process, which was beneficial for the im-

4+

reduction from Ce

to Ce

3+

provement of the cell performances. This research demon-

resulting in the partial internal

electronic short circuit through the electrolyte, as is shown

strates that the construction of the electron-blocking layer

in Figure 9 (a). On the basis of the reaction mechanism men-

with improved composition is an efficient strategy to im-

tioned above, for the cell with GDC10 electrolyte supported

prove the performance of ceria-based solid oxide fuel cells.

by NiO-BZCG, the functional interlayer consisting of Zr, Ni co-doped BaCe0.9Gd0.1O3-δ can be formed and works as the electron-blocking

component between

NiO-BZCG

ASSOCIATED CONTENT

and

Supporting Information. 1. TEM and EDS images in line-

GDC10 (Figure 9 (b)). As is schematically illustrated in Figure

scan mode of YDC20 sintered between two anode pellets. 2.

9 (c), under high temperature sintering, the compacting at-

TEM-EDS elemental mappings of the sample. 3. Impedance

tachment between NiO-BZCG and YDC20 is advantageous

fitting results of different samples. This material is available

for the formation of a new composition due to the metal

free of charge via the Internet at http://pubs.acs.org.

ionic diffusion between electrolyte and anode. According to the in-situ reaction, it is proposed that Zr, Ni, Gd co-doped

H ACS Paragon Plus Environment

Page 9 of 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


AUTHOR INFORMATION

(13)

Corresponding Author

H. High power density thin film SOFCs with YSZ/GDC

Cho, S.; Kim, Y.; Kim, J.-H.; Manthiram, A.; Wang,

bilayer electrolyte. Electrochim. Acta 2011, 56, 5472-5477.

* E-mail address: [email protected].

(14)

Ahn, J. S.; Pergolesi, D.; Camaratta, M. A.; Yoon, H.;

Lee, B. W.; Lee, K. T.; Jung, D. W.; Traversa, E.; Wachsman,

ACKNOWLEDGMENT

E. D. High-performance bilayered electrolyte intermediate

This work was supported by the National Science Founda-

temperature solid oxide fuel cells. Electrochem. Commun.

tions of China (Grant Nos: 51502004, 11404004, and 11474003).

2009, 11, 1504-1507. (15)

Hou, J.; Liu, F. G.; Gong, Z.; Wu, Y. S.; Liu, W. materials

and

Different

(1)

Sm0.075Nd0.075Ce0.85O2−δ for ceria–bismuth bilayer electrolyte

Steele, B. C.; Heinzel, A. Materials for fuel-cell

ceria-based

Gd0.1Ce0.9O2−δ

REFERENCES technologies. Nature 2001, 414, 345-382.

high performance low temperature solid oxide fuel cells. J.

(2)

Power Sources 2015, 299, 32-39.

Shao, Z. P. A high-performance cathode for the next

generation of solid-oxide fuel cells. Nature 2004, 431, 170-173.

(16)

(3)

fuel cell free from internal short circuit. J. Power Sources

Park, S.; Vohs, J. M.; Gorte, R. J. Direct oxidation of

Sun, W. P.; Liu, W. A novel ceria-based solid oxide

hydrocarbons in a solid-oxide fuel cell. Nature 2000, 404,

2012, 217, 114-119.

265-267.

(17)

(4)

efficient SOFC based on samaria-doped ceria (SDC)

Murray, E. P.; Tsai, T.; Barnett, S. A. A direct-

Liu, M. F.; Ding, D.; Bai, Y. H.; He, T.; Liu, M. L. An

methane fuel cell with a ceria-based anode. Nature 2016, 400,

electrolyte. J. Electrochem. Soc. 2012, 159, B661-B665.

649-651.

(18)

(5)

reduction-resistant

Brett, D. J. L.; Atkinson, A.; Brandon, N. P.; Skinner,

Cao, J. F.; Gong, Z.; Hou, J.; Cao, J. F.; Liu, W. Novel Ba(Ce,Zr)1−xGdxO3−δ

electron-blocking

S. J. Intermediate temperature solid oxide fuel cells. Chem.

layer for Gd0.1Ce0.9O2−δ electrolyte in IT-SOFCs. Ceram. Int.

Soc. Rev. 2008, 37, 1568-1578.

2015, 41, 6824-6830.

(6)

(19)

Wachsman, E. D.; Lee, K. T. Lowering the

Cao, J. F.; Gong, Z.; Fan, C. G.; Ji, Y.; Liu, W. The

temperature of solid oxide fuel cells. Science 2011, 334, 935-9.

improvement of barium-containing anode for ceria-based

(7)

electrolyte with electron-blocking layer. J. Alloys Compd.

Fabbri, E.; Pergolesi, D.; Traversa, E. Materials

challenges toward proton-conducting oxide fuel cells: a

2017, 693, 1068-1075.

critical review. Chem. Soc. Rev. 2010, 39, 4355-69.

(20)

(8)

electrolytes for IT-SOFC operation at 500°C. Solid State

Liu, Q. L.; Khor, K. A.; Chan, S. H. High-

Steele, B. C.

H. Appraisal

of Ce1−yGdyO2−y/2

performance low-temperature solid oxide fuel cell with novel

Ionics 2000, 129, 95-110.

BSCF cathode. J. Power Sources 2006, 161, 123-128.

(21)

(9)

Electrical properties of ceria-based oxides and their

Zhang, X.; Robertson, M.; Yick, S.; Deĉes-Petit, C.;

Eguchi, K.; Setoguchi, T.; Inoue, T.; Arai, H.

Styles, E.; Qu, W.; Xie, Y.; Hui, R.; Roller, J.; Kesler, O.; Maric,

application to solid oxide fuel cells. Solid State Ionics 1992,

R.;

52, 165-172.

Ghosh,

D.

Sm0.5Sr0.5CoO3+Sm0.2Ce0.8O1.9

composite

(22)

cathode for cermet supported thin Sm0.2Ce0.8O1.9 electrolyte

Ding, C. S.; Hashida, T. High performance anode-

SOFC operating below 600°C. J. Power Sources 2006, 160,

supported solid oxide fuel cell based on thin-film electrolyte

1211-1216.

and nanostructured cathode. Energ. Environ. Sci. 2010, 3,

(10)

1729-1731.

Eguchi, K.; Setoguchi, T.; Inoue, T.; Arai, H.

Electrical properties of ceria-based oxides and their

(23)

application to solid oxide fuel cells. Solid State Ionics 1992,

GDC-based

52, 165-172.

hydrocarbon fuels. J. Electrochem. Soc. 2004, 151, A1128-A1133.

(11)

Steele,

B.

C.

H.

Appraisal

of

(24)

Ce1-yGdyO2-y/2

Zha, S. W.; Moore, A.; Abernathy, H.; Liu, M. L. low-temperature

SOFCs

powered

by

Sun, W. P.; Shi, Z.; Qian, J.; Wang, Z. T.; Liu, W. In-

electrolytes for IT-SOFC operation at 500°C. Solid State

situ

Ionics 2000, 129, 95-110.

core/shell electron-blocking layer towards Ce0.8Sm0.2O2−δ-

(12)

formed

Ce0.8Sm0.2O2−δ@Ba(Ce,

Zr)1−x(Sm,

Y)xO3−δ

based solid oxide fuel cells with high open circuit voltages.

Liu, Q. L.; Khor, K. A.; Chan, S. H.; Chen, X. J.

Anode-supported solid oxide fuel cell with yttria-stabilized

Nano Energy 2014, 8, 305-311.

zirconia/gadolinia-doped ceria bilalyer electrolyte prepared

(25)

by wet ceramic co-sintering process. J. Power Sources 2006,

BaZr0.1Ce0.7Y0.2O3-δ/Ce0.8Sm0.2O2-δ electrolyte membranes for

Sun, W. P.; Shi, Z.; Wang, Z.; Liu, W. Bilayered

162, 1036-1042.

I ACS Paragon Plus Environment


solid oxide fuel cells with high open circuit voltages. Journal of Membrane Science 2015, 476, 394-398. (26)

White, B. D.; Kesler, O. Implications of electronic

short circuiting in plasma sprayed solid oxide fuel cells on electrode

performance

evaluation

by

electrochemical

impedance spectroscopy. J. Power Sources 2008, 177, 104-110. (27)

Lee, Y.; Joo, J. H.; Choi, G. M. Effect of electrolyte

thickness on the performance of anode-supported ceria cells. Solid State Ionics 2010, 181, 1702-1706. (28)

Matsumoto, H.; Kawasaki, Y.; Ito, N.; Enoki, M.;

Ishihara, T. Relation between electrical conductivity and chemical stability of BaCeO3-based proton conductors with different trivalent dopants. Electrochem. Solid-State Lett. 2007, 10, B77-B80. (29)

Tu, C. S.; Chien, R. R.; Schmidt, V. H.; Lee, S. C.;

Huang,

C.

C.;

Tsai,

C.

L.

Thermal

stability

of

Ba(Zr0.8−xCexY0.2)O2.9 ceramics in carbon dioxide. J. Appl. Phys. 2009, 105, 103504. (30)

Katahira, K.; Kohchi, Y.; Shimura, T.; Iwahara, H.

Protonic conduction in Zr-substituted BaCeO3. Solid State Ionics 2000, 138, 91-98. (31)

Zuo, C. D.; Zha, S. W.; Liu, M. L.; Hatano, M.;

Uchiyama, M. Ba(Zr0.1Ce0.7Y0.2)O3-delta as an electrolyte for low-temperature solid-oxide fuel cells. Adv. Mater. 2014, 18, 3318-3320. (32)

Guo, Y. M.; Lin, Y.; Ran, R.; Shao, Z. P. Zirconium

doping effect on the performance of proton-conducting BaZryCe0.8−yY0.2O3−δ (0.0≤y≤0.8) for fuel cell applications. J. Power Sources 2009, 193, 400-407. (33)

Huang,

Q.-A.;

Liu,

M.;

Liu,

M.

Impedance

spectroscopy study of an SDC-based SOFC with high open circuit voltage. Electrochim. Acta 2015, 177, 227-236. (34)

Kreuer, K. D. Proton-Conductingoxides. Annu. Rev.

Mater. Sci. 2003, 33, 333-359. (35)

Ryu, K. H.; Haile, S. M. Chemical stability and

proton conductivity of doped BaCeO3–BaZrO3 solid solutions. Solid State Ionics 1999, 125, 355-367. (36)

Konwar, D.; Nguyen, N. T. Q.; Yoon, H. H.

Evaluation of BaZr0.1Ce0.7Y0.2O3-δ electrolyte prepared by carbonate precipitation for a mixed ion-conducting SOFC. Int. J. Hydrogen Energy 2015, 40, 11651-11658. (37)

Medvedev, D.; Murashkina, A.; Pikalova, E.; Demin,

A.; Podias, A.; Tsiakaras, P. BaCeO3: Materials development, properties and application. Prog. Mater Sci. 2014, 60, 72-129.

J ACS Paragon Plus Environment

Page 10 of 11

Page 11 of 11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents Artwork

K Environment ACS Paragon Plus

An Efficient Electron-Blocking Interlayer Induced by Metal Ion Diffusion

Recommend Documents