Highly stable dual-phase Y0.8Ca0.2Cr0.8Co0.2O3–Sm0.2Ce0.8O1.9 ceramic composite membrane for oxygen separation

Author’s Accepted Manuscript Highly Stable Dual-Phase Y0.8Ca0.2Cr0.8Co0.2O3 Sm0.2Ce0.8O1.9 Ceramic Composite Membrane for Oxygen Separation Kyung Joong Yoon, Olga A. Marina www.elsevier.com/locate/memsci

PII: DOI: Reference:

S0376-7388(15)30296-9 http://dx.doi.org/10.1016/j.memsci.2015.10.064 MEMSCI14087

To appear in: Journal of Membrane Science Received date: 6 July 2015 Revised date: 15 September 2015 Accepted date: 28 October 2015 Cite this article as: Kyung Joong Yoon and Olga A. Marina, Highly Stable DualPhase Y0.8Ca0.2Cr0.8Co0.2O3 - Sm0.2Ce0.8O1.9 Ceramic Composite Membrane for Oxygen Separation, Journal of Membrane Science, http://dx.doi.org/10.1016/j.memsci.2015.10.064 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Highly Stable Dual-Phase Y0.8Ca0.2Cr0.8Co0.2O3 - Sm0.2Ce0.8O1.9 Ceramic Composite Membrane for Oxygen Separation

Kyung Joong Yoon1,2, Olga A. Marina1,*

1

Pacific Northwest National Laboratory, Richland, WA 99352, USA 2

Korea Institute of Science and Technology, Seoul 135-791, Korea

*Corresponding Author: Pacific Northwest National Laboratory P.O. Box 999, Richland, WA 99352, USA Tel: +1-509-375-2337 E-mail: [email protected] 1

Abstract

A highly stable ceramic composite membrane composed of Ca- and Co-doped yttrium chromite, Y0.8Ca0.2Cr0.8Co0.2O3 (YCCC), and samaria-doped ceria, Sm0.2Ce0.8O1.9 (SDC), was demonstrated for oxygen separation. Homogeneously dispersed nano-scale composite powders were synthesized by a single-step combustion process based on the glycine-nitrate method. Dense composite membranes were achieved having submicron grain sizes and well-percolated electronic and ionic conduction pathways. Densification of the composite membrane was assisted by liquid phase sintering caused by cobalt-doping in yttrium chromite, and gas-tight membranes are fabricated at 1400oC. The YCCC and SDC phases were chemically and thermomechanically compatible at both processing and operating temperatures. The composite membrane exhibited an oxygen permeation flux comparable to those of the state-of-the-art single-phase membrane materials and excellent stability in harsh operating conditions under a H2-CO2 environment for long-term operation, which suggests potential application in various combustion and fuel production processes.

Key Words: Dual-phase stable ceramic membrane; High-temperature oxygen separation; Oxygen permeability; High-purity oxygen production; Doped chromite -ceria composite

2

1. Introduction High-temperature oxygen transport membranes based on mixed ionic- and electronicconducting (MIEC) ceramics are receiving increasing attention due to their potential applications for high-purity oxygen production, oxyfuel combustion, hydrogen/syngas production, coal gasification, and waste recovery [1, 2]. Dense MIEC membranes exclusively allow the permeation of oxygen ions in the presence of an oxygen partial pressure gradient because the oxygen ionic flux is counterbalanced by the flux of electrons to form an internal short circuit. For practical applications, an MIEC membrane should be gas-tight, highly oxygen permeable, chemically stable and inexpensive. Most candidate materials for use as ceramic MIEC membrane are either perovskite or fluorite structures [1]. Single-phase perovskite-type oxides such as La1-xSrxCo1-yFeyO3-δ exhibit high oxygen permeability due to their high ambipolar conductivity, but practical applications have been limited because of their chemical and dimensional instability in a large oxygen chemical potential gradient, reactivity with CO2 and relatively high thermal expansion behavior [3]. On the other hand, single-phase fluorite materials such as doped zirconia and doped ceria possess adequate stability under the practical operating conditions, but oxygen permeability is low because of their low electronic conductivity [4, 5]. Alternatively, dual-phase composite membranes composed of oxygen ion-conducting ceramics and electron-conducting noble metals have been proposed [6, 7]. In this approach, the formation of the percolative paths for both phases is extremely important to obtain sufficient oxygen permeation flux [8], and in practice, at least 30~40 vol. % of noble metal such as Pt, Pd or Ag is required to form a continuous path for electronic conduction [8, 9], which is not 3

acceptable from an economic perspective. To reduce the materials costs, all-ceramic composite membranes composed of a fluorite ionic conductor and a single- or double-perovskite electronic conductor,

such

as

Zr0.84Y0.16O1.92-La0.8Sr0.2MnO3-δ

[10,

11],

Zr0.84Y0.16O1.92-

La0.8Sr0.2Cr0.5Fe0.5O3-δ [12, 13], Ce0.8Gd0.2O1.95-La0.7Sr0.3MnO3-δ [14, 15], Ce0.9Gd0.1O1.95La0.6Sr0.4CoO3-δ [16], Ce0.9Gd0.1O1.95-La0.6Sr0.4FeO3-δ [16], Ce0.9Gd0.1O2-δ-La0.6Sr0.4Co0.2Fe0.8O3-δ [17], Ce0.9Gd0.1O1.95-Ba0.5Sr0.5Co0.8Fe0.2O3-δ [18, 19], Ce0.8Sm0.2O2-δ-La0.7Ca0.3CrO3-δ [20], Ce0.8Sm0.2O2-δ-La0.8Sr0.2CrO3-δ

[21,

22],

Ce0.8Sm0.2O2-δ-Ba0.95La0.05Fe1-xZrxO3-δ

[23],

Ce0.85Sm0.15O1.925-Sm0.6Sr0.4Al0.3Fe0.7O3-δ [24], Ce0.8Sm0.2O2-δ-LnBaCo2O5+δ (Ln=La, Pr, Nd, Sm, Y) [25-28], have been investigated. In all-ceramic composite membranes, the chemical interaction between the two phases readily leads to significant degradation at high temperatures, such that stability issues remain a concern as with single-phase perovskite materials [29]. Therefore, the development of the dual-phase ceramic composite membrane with sufficient oxygen permeability and stability is highly desirable for commercial development of MIEC membrane technology. Ca- and Co-doped yttrium chromite (YCCC), which has been developed as an interconnect material for solid oxide fuel cells (SOFCs), possesses excellent electronic conductivity, sinterability and stability over a wide range of oxygen partial pressure [30]. Samaria-doped ceria (SDC) is a well-known electrolyte material for SOFCs with high ionic conductivity and phase stability in both oxidizing and reducing environments [31]. The chemical compatibility of these two materials was also confirmed for application of the SOFC composite anode [32]. A composite of these two materials could possibly overcome the limitations of the conventional MIEC membrane materials, and may be a good candidate for use in oxygen separation membrane reactors operating under harsh conditions. In this work, the YCCC–SDC 4

composite powder was synthesized by a single-step combustion process based on the glycinenitrate combustion synthesis method, and dense MIEC composite membranes were fabricated via a low-temperature sintering process. The oxygen permeation characteristics and long-term stability were evaluated under various operating conditions, relative to practical oxygen separation from air and to partial oxidation of methane.

2. Experimental YCCC–SDC composite powders were synthesized by a single-step combustion process based on the glycine-nitrate combustion method [33]. All of the nitrate precursors for the composite (yttrium, calcium, chromium, cobalt, samarium and cerium) were mixed in water with glycine according to the stoichiometric ratio (50 wt % of Y0.8Ca0.2Cr0.8Co0.2O3 and 50 wt % of Sm0.2Ce0.8O1.9) and co-burned in a single combustion step to form the dual phase composite. The obtained powder was calcined at 1100oC for 2 hours in air, and the formation of the composite phases was confirmed using X-ray diffraction (XRD) analysis. The powder morphology was investigated after calcination using transmission electron microscopy (TEM). Individual YCCC and SDC powders were synthesized and analyzed separately, as described elsewhere [30]. Composite disc membranes with various thicknesses (1.3, 1.9, and 2.4 mm) were fabricated by uniaxially pressing the composite powder at 35 MPa followed by isostatic pressing at 200 MPa and sintering at 1400oC for 4 hours in air. The area of the membrane was 1.98 cm2. After sintering, the phase purity of the composite membrane was assessed using powder x-ray diffraction (XRD) of crushed samples. The relative density of sintered samples was measured using the Archimedes density measurement. Sintered samples were sectioned and impregnated 5

with epoxy under vacuum. After the epoxy hardened, the samples were polished down to 0.25 μm and examined using scanning electron microscope (SEM). To investigate the effect of Codoping in yttrium chromite on the sintering behavior of the composite membrane, a composite membrane without Co-doping (Y0.8Ca0.2CrO3 (YCC) - SDC) was prepared using same procedure, and its cross-section was analyzed using SEM. For oxygen permeation measurements, the membranes were mounted between two alumina tubes and sealed with gold o-rings at 950oC by pressure loading. Gold o-rings were used instead of glass sealant to avoid chemical contamination on the membrane surface [34]. Air was supplied to the feed side at a flow rate of 30 ml min-1, and various sweeping gases such as N2, forming gas (3% H2 balanced with N2) and a mixture of 50% CO2 and 50% forming gas were supplied to the permeate side of the membrane at the same flow rate. The oxygen partial pressure of the output gas from the permeate side was measured using a zirconia-based oxygen sensor. The measurements were performed in the temperature range of 250-950oC, and the oxygen flux was obtained based on the assumption that the increase in the total amount of oxygen in the permeate side from the baseline was entirely due to the oxygen ion permeation through the membrane. A long-term test was performed at 950oC with a mixture of 50% CO2 and 50% forming gas in the permeate side. YCCC-SDC phase stability after exposure to various gas environments was verified using XRD analysis.

3. Results and Discussion

6

X-ray diffraction analyses of calcined powders, sintered compacts, and sintered membranes following extended exposure to H2/CO2 revealed the presence of two separate phases, Figure 1. The two phases were identified as the perovskite YCCC and fluorite SDC. This result indicates that a composite of two separate phases can be prepared in one step using simple and cost-effective glycine-nitrate combustion method. The chemical compatibility between YCCC and SDC was verified by examining the XRD pattern of the composite powder obtained by

Intensity (a.u.)

After Exposure to H2 and CO2 at 950oC

After Sintering at 1400oC

After Calcination at 1100oC

YCCC

SDC

20

30

40

50

60

70

80

2 theta (degree) Figure 1. XRD patterns of YCCC-SDC composite powder synthesized by the single-step glycine-nitrate process after calcination at 1100oC in air, sintering at 1400oC and exposure to H2 and CO2 for over 350 hours at 950oC. Patterns of pure YCCC and SDC powders are given as well. 7

crushing the sintered pellet at 1400oC, also shown in Figure 1. No indication of a reaction product or major peak shift was observed, implying that a processing temperature up to 1400oC can be used for the densification of the membrane without causing problems associated with chemical interactions between the two phases. In addition, Figure 1 contains XRD pattern obtained from the surface of the sample exposed to H2 and CO2 (50% forming gas + 50% CO2) at 950oC for over 350 hours in a long-term test. There was no indication of phase decomposition or carbonate formation, showing the stability of the composite membrane in reducing and CO2containing environments for the conditions tested at 850oC and above. As shown in Figure 2, the morphology of calcined composite powders was investigated by TEM after calcination at 1100oC. The image reveals homogeneous mixture of the extremely fine particles with the primary particle size of 50-70 nm. Due to excellent powder characteristics such as small particle size and narrow size distribution, enhanced sinterability and microstructural control are expected in subsequent fabrication of the dense composite membranes. In particular, because the two phases exhibit extremely similar powder morphology, minimal hydrostatic tensile stress and geometrical constraints, which would originate from the difference in particle sizes, are expected during sintering, leading to no interference to the natural sintering stresses [35]. The preparation method of the composite powder plays a critical role in determining the properties of the dual phase membrane [24], and based on the particle characteristics described in Figure 1 and 2, the solution-based combustion process presented in this study is considered to be a superior processing route when compared to the conventional mechanical mixing method in terms of the particle size, mixing scale, compositional / morphological homogeneity and processing complexity.

8

Figure 2. TEM image of the YCCC-SDC composite powder calcined at 1100oC in air.

Dense YCCC-SDC composite membranes were fabricated by sintering the powder compacts at 1400oC and examined using SEM. A typical micrograph of the membrane is given in Figure 3 (a). The SDC phase appears in white, YCCC does in gray, and the pores are black. The SEM micrographs clearly showed well-connected conduction paths for both electrons and oxygen ions with a negligible amount of isolated pores. Homogeneous mixing of the YCCC and SDC particles resulting from the solution-based synthesis route led to percolative distribution of the electronic- and ionic-conduction paths, and high ambipolar conductivity is expected for oxygen permeation. The total conductivity of the dense YCCC-SDC composite was measured to be 22 S cm-1 at 850oC in air and that of the pure YCCC was 49 S cm-1 under the same condition [30]. The total conductivity of the YCCC-SDC composite was dominated by the electrical conductivity of YCCC, and the conductivity data verified the formation of a percolative network by the electron-conducting YCCC phase.

9

Figure 3. SEM images of (a) YCCC (with Co-doping)-SDC and (b) YCC (without Co-doping)SDC membranes sintered at 1400oC. YCCC and YCC are grey, SDC is white, and pores are black.

The relative density of the sintered membrane was over 97% of the theoretical value based on the Archimedes density measurement, which ensures gas-tightness across the membrane. The excellent densification behavior of the composite membrane at a relatively low sintering temperature can be attributed to the liquid phase sintering of YCCC. In general, chromite-based ceramic materials exhibit extremely poor sintering characteristics, which has been ascribed to the formation of Cr2O3 thin layers at the inter-particle neck during the initial stage of sintering [36]. However, cobalt doping lowers the sintering temperature of yttrium chromite due to the formation of the transient liquid phase, leading to nearly complete densification at 1400oC [30].

10

To illustrate the effect of the liquid phase sintering on densification behavior of the composite membrane, the composite powder without Co-doping in yttrium chromite (YCCSDC) was synthesized through the same process, and the powder compact was sintered at 1400oC. The SEM image of the cross-section of the membrane without Co-doping in Figure 3 (b) shows a highly porous structure. Densification of the composite membrane at a relatively low sintering temperature would minimize the technical issues associated with the high-temperature processing, such as the chemical interaction and thermal expansion mismatch between two phases [37]. For example, in Ce0.8Gd0.2O2-δ – La0.7Sr0.3MnO3-δ composite membranes, the diffusion of lanthanum and strontium from La0.7Sr0.3MnO3-δ into Ce0.8Gd0.2O2-δ led to the formation of poorly conducting phases along the grain boundaries of ceria [14]. In YCCC-SDC membranes, such chemical compatibility issues are not expected because the chemical compatibility was confirmed up to 1400oC by the XRD analysis shown in Figure 1. In addition, the thermal expansion coefficient (TEC) of YCCC (12.2 x 10-6 K-1 [30]) is very close to that of SDC (12.8 x 10-6 K-1 [38, 39]), which ensures that there is minimal thermal stresses within the composite membrane. Oxygen permeability was assessed as a function of temperature for membranes of various thicknesses. Figure 4 (a) shows the oxygen permeation flux through composite membranes measured with N2 on the permeate side (pO2=~10-5 atm) and air on the feed side at 250 - 950oC for 1.3, 1.9, and 2.4 mm thick membranes. The oxygen flux increased with increasing temperature because the oxygen permeation through the MIEC membrane is a thermally activated process [1]. Below 500oC, the oxygen partial pressure at the permeate side remained essentially the same as the background level and the permeation flux through the membrane was negligible, which confirmed that the membrane and sealants were gas-tight. The oxygen 11

permeation flux increased with decreasing membrane thickness and was measured to be 2.3×10-7 mol cm-2 s-1 for a 1.3 mm-thick membrane at 950oC, which is substantially higher than the reported values for the conventional ceramic-noble metal composite membranes (e.g. 4.2×10-8 mol cm-2 s-1 for 2 mm-thick YSZ-Pd at 1100oC [8]) and comparable to the single-phase perovskite or dual-phase ceramic composite membranes (e.g., 1.06×10-7 mol cm-2 s-1 for 1 mmthick La0.6Sr0.4Co0.4Fe0.6O3-δ at 1100K [40] and 1.53×10-7 mol cm-2 s-1 for 1 mm-thick La0.6Sr0.4CoO3-δ – Ce0.9Gd0.1O1.95 at 800oC [16]). To identify the rate limiting process, the oxygen permeation flux was plotted as a function of reciprocal membrane thickness between 850 and 950oC in Figure 4 (b). The oxygen permeation process through a dense MIEC membrane involves a surface exchange reaction and bulk diffusion of the charged species [1], and the overall oxygen permeation rate is limited by the slowest process [41, 42]. If the oxygen permeation were limited by the surface reaction kinetics, the permeation flux would be independent of the membrane thickness [1]. If the bulk diffusion is the rate limiting process, the oxygen flux can be expressed by the Wagner equation [43]:

J O2  

ln  ''O 2   RT el ion d ln  O 2  2 16F L ln  'O 2  el   ion

(1)

where JO2 is the oxygen permeation flux, R is the gas constant, T is the temperature, F is the Faraday constant, L is the membrane thickness, el is the electronic conductivity of the membrane, ion is the ionic conductivity of the membrane, μ΄O2 is the oxygen chemical potential on the feed side, and μ΄΄O2 is the oxygen chemical potential on the permeate side. In this case, the oxygen permeation flux is inversely proportional to the thickness of the membrane at the fixed 12

oxygen chemical potential gradient across the membrane. In Figure 4 (b), the oxygen flux and the reciprocal thickness of the membrane show a linear relationship, and the extrapolations of the fitting lines pass through the origin within the experimental error, which indicates that the ratelimiting process is the bulk diffusion rather than surface exchange. Therefore, oxygen permeation flux can be further improved by reducing the membrane thickness, and eventually, the thin film membrane deposited on a porous support would be a desirable design to maximize the performance [44]. The oxygen permeation flux through the 1.3 mm-thick membrane was measured with air on the feed side and various sweep gases (N2, forming gas (3% H2+97% N2) and 50% forming gas (3% H2+97% N2) mixed with 50% CO2) on the permeate side at 700 - 950oC, as shown in Figure 5 (a). The oxygen permeation flux exhibited the maximum value with the forming gas (3% H2+97% N2) on the permeate side and decreased with mixing the forming gas (3% H2+97% N2) with CO2, which can be explained by the reduction of the driving force for oxygen permeation, i.e. oxygen partial pressure gradient across the membrane, and by adsorption of CO2 on the surface of the membrane, retarding the oxygen exchange reactions. The oxygen permeation flux further decreased by supplying N2 as a sweep gas. The measured flux reached 4.6×10-6 mol cm-2 s-1 at 950oC with air and forming gas (3% H2+97% N2) condition, which is equivalent to 6.7 ml cm-2 min-1 (STP). Because an oxygen flux of 1 ~ 10 ml cm-2 min-1 (STP) is considered to be viable for commercial use [45, 46], the YCCC-SDC composite membrane could readily meet the targets for various practical applications. The activation energies obtained from the slopes in Figure 5 (a) range from 82 to 90 kJ mol-1 under various gas environments. These values agree reasonably well with the activation energies of oxygen ionic diffusion in SDC (82-

13

(a) -7

2.5x10

1.3 mm 1.9 mm 2.4 mm

-7

-2

JO2 (mol s cm )

2.0x10

-7

-1

1.5x10

-7

1.0x10

-8

5.0x10

0.0 400

600

800

1000

o

Temperature ( C)

(b) -7

2.5x10

o

950 C o 900 C o 850 C

-7

-2

JO2 (mol s cm )

2.0x10

-7

-1

1.5x10

-7

1.0x10

-8

5.0x10

0.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

-1

1/L (mm )

Figure 4. (a) Oxygen permeation flux as a function of temperature for the membranes with different thicknesses (1.3, 1.9, and 2.4 mm), and (b) oxygen flux as a function of reciprocal membrane thickness between 850 and 950oC with air on the feed side and N2 on the permeate side. 14

(a)

-2

log10 JO2 (mol s cm )

-5

-1

-6

-7

-8

Air / 100% Forming Gas (3% H2 + 97% N2) Air / 50% CO2+ 50% Forming Gas (3% H2 + 97% N2) Air / 100% N2

-9 0.8

0.9 3

1.0 -1

10 /T (K )

(b) log10 JO2 (mol s-1 cm-2)

-5.4 Temperature: 950oC Air / 50% CO2 + 50% Forming Gas

-5.5 -5.6 -5.7 -5.8 -5.9 -6.0 0

50

100

150

200

250

300

350

Time (Hours)

Figure 5. (a) Oxygen permeation flux through 1.3 mm-thick membrane under various gas environments (N2, forming gas (3% H2+97% N2), and 50% CO2 + 50% forming gas (3% H2+97% N2)) on the permeate side and air on the feed side between 700 and 950oC and (b) longterm test results performed at 950oC with air on the feed side and 50% CO2 + 50% forming gas on the permeate side. 15

93 kJ mol-1 [47-51]), which supports that the rate-limiting process of the oxygen permeation is bulk diffusion of oxygen ions. The long-term test was performed at 950oC with air in the feed side and 50% CO2+50% forming gas (3% H2+97% N2) in the permeate side in Figure 5 (b). The initial flux was 2.1×10-6 mol cm-2 s-1, and degradation rate was less than 2% / 350hr. The membrane remained structurally intact, and no change in the XRD pattern was detected after long-term operation (Figure 1). In general, the majority of the perovskite materials used for oxygen separation membranes exhibit chemical and dimensional instability upon exposure to H2 and CO2 [14], showing rapid degradation within 100 hours of operation caused by phase decomposition, defect ordering and surface passivation [52, 53]. The excellent stability in the H2 and CO2 environments presented in this paper suggests that the oxygen separation process based on YCCC-SDC composite membrane can be integrated with various combustion and fuel production processes, which would improve efficiency, enhance selectivity and aid in CO2 capture [54].

4. Conclusions YCCC-SDC ceramic composite membranes exhibited excellent performance and stability under the various operating conditions. Single step glycine-nitrate process produces the nanoscale composite powders with a narrow size distributions and homogeneous dispersion, enabling complete densification at the relatively low processing temperatures. Sintering behavior was further improved by liquid phase sintering associated with cobalt-doping in yttrium chromite. The oxygen permeation flux of the YCCC-SDC membrane is comparable to that of the state-of16

the-art single-phase perovskite membranes and superior to the conventional dual-phase composite membranes. Because the rate-limiting process of oxygen permeation was bulk ionic diffusion for membrane > ~ 2mm in thickness, the performance of the membrane can be further improved by employing the supported configuration and reducing the membrane thickness. Because the composite membrane was highly stable upon exposure to H2 and CO2, it can be integrated with various combustion and fuel production processes operating in harsh conditions.

5. Acknowledgements This research was financially supported by the institutional research programs of the Pacific Northwest National Laboratory, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy, and Korea Institute of Science and Technology.

6. References [1] J. Sunarso, S. Baumann, J.M. Serra, W.A. Meulenberg, S. Liu, Y.S. Lin, J.C. Diniz da Costa, Mixed ionic-electronic conducting (MIEC) ceramic-based membranes for oxygen separation, Journal of Membrane Science, 320 (2008) 13-41. [2] T.J. Mazanec, T.L. Cable, J.G. Frye, Electrocatalytic cells for chemical reaction, Solid State Ionics, 53-56 (1992) 111-118. [3] J. Yi, M. Schroeder, T. Weirich, J. Mayer, Behavior of Ba(Co, Fe, Nb)O3-δ perovskite in CO2-containing atmospheres: Degradation mechanism and materials design, Chemistry of Materials, 22 (2010) 6246-6253. 17

[4] Y. Nigara, J. Mizusaki, M. Ishigame, Measurement of oxygen permeability in CeO2 doped CSZ, Solid State Ionics, 79 (1995) 208-211. [5] D.P. Fagg, I.P. Marozau, A.L. Shaula, V.V. Kharton, J.R. Frade, Oxygen permeability, thermal expansion and mixed conductivity of GdxCe0.8-xPr0.2O2, x=0, 0.15, 0.2, Journal of Solid State Chemistry, 179 (2006) 3347-3356. [6] J. Kim, Y.S. Lin, Synthesis and oxygen permeation properties of ceramic-metal dual-phase membranes, Journal of Membrane Science, 167 (2000) 123-133. [7] E. Capoen, M.C. Steil, G. Nowogrocki, M. Malys, C. Pirovano, A. Löfberg, E. BordesRichard, J.C. Boivin, G. Mairesse, R.N. Vannier, Oxygen permeation in bismuth-based materials. Part I: Sintering and oxygen permeation fluxes, Solid State Ionics, 177 (2006) 483488. [8] C.S. Chen, B.A. Boukamp, H.J.M. Bouwmeester, G.Z. Cao, H. Kruidhof, A.J.A. Winnubst, A.J. Burggraaf, Microstructural development, electrical properties and oxygen permeation of zirconia-palladium composites, Solid State Ionics, 76 (1995) 23-28. [9] J.E.T. Elshof, N.Q. Nguyen, M.W.D. Otter, H.J.M. Bouwmeester, Oxygen Permeation Properties of Dense Bi1.5Er0.5O3-Ag Cermet Membranes, Journal of The Electrochemical Society, 144 (1997) 4361-4366. [10] W. Li, J.J. Liu, C.S. Chen, Hollow fiber membrane of yttrium-stabilized zirconia and strontium-doped lanthanum manganite dual-phase composite for oxygen separation, Journal of Membrane Science, 340 (2009) 266-271. [11] Y. Ji, J.A. Kilner, M.F. Carolan, Electrical properties and oxygen diffusion in yttriastabilised zirconia (YSZ)-La0.8Sr0.2MnO3 (LSM) composites, Solid State Ionics, 176 (2005) 937943. 18

[12] J.J. Liu, T. Liu, W.D. Wang, J.F. Gao, C.S. Chen, Zr0.84Y0.16O1.92–La0.8Sr0.2Cr0.5Fe0.5O3−δ dual-phase composite hollow fiber membrane targeting chemical reactor applications, Journal of Membrane Science, 389 (2012) 435-440. [13] J.J. Liu, S.Q. Zhang, W.D. Wang, J.F. Gao, W. Liu, C.S. Chen, Partial oxidation of methane in a Zr0.84Y0.16O1.92–La0.8Sr0.2Cr0.5Fe0.5O3−δ hollow fiber membrane reactor targeting solid oxide fuel cell applications, Journal of Power Sources, 217 (2012) 287-290. [14] V.V. Kharton, A.V. Kovalevsky, A.P. Viskup, F.M. Figueiredo, A.A. Yaremchenko, E.N. Naumovich, F.M.B. Marques, Oxygen permeability of Ce0.8Gd0.2O2--La0.7Sr0.3MnO3- composite membranes, Journal of The Electrochemical Society, 147 (2000) 2814-2821. [15] V.V. Kharton, A.V. Kovalevsky, A.P. Viskup, F.M. Figueiredo, A.A. Yaremchenko, E.N. Naumovich, F.M.B. Marques, Oxygen permeability and Faradaic efficiency of Ce0.8Gd0.2O2- La0.7Sr0.3MnO3- composites, Journal of the European Ceramic Society, 21 (2001) 1763-1767. [16] A.J. Samson, M. Søgaard, P. Vang Hendriksen, (Ce,Gd)O2−δ-based dual phase membranes for oxygen separation, Journal of Membrane Science, 470 (2014) 178-188. [17] H. Huang, S. Cheng, J. Gao, C. Chen, J. Yi, Phase-inversion tape-casting preparation and significant performance enhancement of Ce0.9Gd0.1O1.95–La0.6Sr0.4Co0.2Fe0.8O3−δ dual-phase asymmetric membrane for oxygen separation, Materials Letters, 137 (2014) 245-248. [18] J. Xue, Q. Liao, Y. Wei, Z. Li, H. Wang, A CO2-tolerance oxygen permeable 60Ce0.9Gd0.1O2−δ–40Ba0.5Sr0.5Co0.8Fe0.2O3−δ dual phase membrane, Journal of Membrane Science, 443 (2013) 124-130. [19] C. Zhang, R. Ran, G.H. Pham, K. Zhang, J. Liu, S. Liu, Ce0.9Gd0.1O2-δ membranes coated with porous Ba0.5Sr0.5Co0.8Fe0.2O3-δ for oxygen separation, RSC Advances, 5 (2015) 5379-5386.

19

[20] T.F. Tian, W. Li, T. Liu, C.S. Chen, Preparation and oxygen permeability of Ce0.8Sm0.2O2−δLa0.7Ca0.3CrO3−δ dual-phase composite hollow fiber membrane, Solid State Ionics, 225 (2012) 690-694. [21] B. Wang, J. Yi, L. Winnubst, C. Chen, Stability and oxygen permeation behavior of Ce0.8Sm0.2O2−δ–La0.8Sr0.2CrO3−δ composite membrane under large oxygen partial pressure gradients, Journal of Membrane Science, 286 (2006) 22-25. [22] J. Yi, Y. Zuo, W. Liu, L. Winnubst, C. Chen, Oxygen permeation through a Ce0.8Sm0.2O2−δ– La0.8Sr0.2CrO3−δ dual-phase composite membrane, Journal of Membrane Science, 280 (2006) 849-855. [23] H. Cheng, L. Luo, W. Yao, X. Lu, X. Zou, Z. Zhou, Novel cobalt-free CO2-tolerant dualphase membranes of Ce0.8Sm0.2O2−δ–Ba0.95La0.05Fe1−xZrxO3−δ for oxygen separation, Journal of Membrane Science, 492 (2015) 220-229. [24] X. Zhu, Y. Liu, Y. Cong, W. Yang, Ce0.85Sm0.15O1.925–Sm0.6Sr0.4Al0.3Fe0.7O3 dual-phase membranes: One-pot synthesis and stability in a CO2 atmosphere, Solid State Ionics, 253 (2013) 57-63. [25] T. Chen, H. Zhao, N. Xu, Y. Li, X. Lu, W. Ding, F. Li, Synthesis and oxygen permeation properties of a Ce0.8Sm0.2O2−δ–LaBaCo2O5+δ dual-phase composite membrane, Journal of Membrane Science, 370 (2011) 158-165. [26] T. Chen, H. Zhao, Z. Xie, N. Xu, Y. Lu, Oxygen permeability of Ce0.8Sm0.2O2−δ– LnBaCo2O5+δ (Ln=La, Nd, Sm, and Y) dual-phase ceramic membranes, Ionics, 21 (2015) 16831692.

20

[27] T. Chen, H. Zhao, Z. Xie, Y. Lu, N. Xu, Improved oxygen permeability of Ce0.8Sm0.2O2−δ– PrBaCo2O5+δ dual-phase membrane by surface-modifying porous layer, International Journal of Hydrogen Energy, 37 (2012) 19133-19137. [28] T. Chen, H. Zhao, Z. Xie, J. Wang, Y. Lu, N. Xu, Ce0.8Sm0.2O2−δ–PrBaCo2O5+δ dual-phase membrane: Novel preparation and improved oxygen permeability, Journal of Power Sources, 223 (2013) 289-292. [29] S.M. Hashim, A.R. Mohamed, S. Bhatia, Current status of ceramic-based membranes for oxygen separation from air, Advances in Colloid and Interface Science, 160 (2010) 88-100. [30] K.J. Yoon, C.N. Cramer, E.C. Thomsen, C.A. Coyle, G.W. Coffey, O.A. Marina, Calciumand cobalt-doped yttrium chromites as an interconnect material for solid oxide fuel cells, Journal of The Electrochemical Society, 157 (2010) B856-B861. [31] Y.P. Fu, S.B. Wen, C.H. Lu, Preparation and characterization of samaria-doped ceria electrolyte materials for solid oxide fuel cells, Journal of the American Ceramic Society, 91 (2008) 127-131. [32] K.J. Yoon, C.A. Coyle, O.A. Marina, Doped yttrium chromite-ceria composite as a redoxstable and sulfur-tolerant anode for solid oxide fuel cells, Electrochem. Commun., 13 (2011) 1400-1403. [33] L.A. Chick, L.R. Pederson, G.D. Maupin, J.L. Bates, L.E. Thomas, G.J. Exarhos, Glycinenitrate combustion synthesis of oxide ceramic powders, Materials Letters, 10 (1990) 6-12. [34] A. Vivet, P.M. Geffroy, V. Coudert, J. Fouletier, N. Richet, T. Chartier, Influence of glass and gold sealants materials on oxygen permeation performances in La0.8Sr0.2Fe0.7Ga0.3O3−δ perovskite membranes, Journal of Membrane Science, 366 (2011) 132-138.

21

[35] L.C. De Jonghe, M.N. Rahaman, C.H. Hsueh, Transient stresses in bimodal compacts during sintering, Acta Metallurgica, 34 (1986) 1467-1471. [36] W.Z. Zhu, S.C. Deevi, Development of interconnect materials for solid oxide fuel cells, Materials Science and Engineering A, 348 (2003) 227-243. [37] A.L. Shaula, V.V. Kharton, F.M.B. Marques, Phase interaction and oxygen transport in La0.8Sr0.2Fe0.8Co0.2O3-(La0.9Sr0.1)0.98Ga0.8Mg0.2O3 composites, Journal of the European Ceramic Society, 24 (2004) 2631-2639. [38] M. Mori, T. Yamamoto, H. Itoh, H. Inaba, H. Tagawa, Thermal expansion of nickelzirconia anodes in solid oxide fuel cells during fabrication and operation, Journal of the Electrochemical Society, 145 (1998) 1374-1381. [39] Q. Xu, D.P. Huang, F. Zhang, W. Chen, M. Chen, H.X. Liu, Structure, electrical conducting and thermal expansion properties of La0.6Sr0.4Co0.8Fe0.2O3−δ–Ce0.8Sm0.2O2−δ composite cathodes, Journal of Alloys and Compounds, 454 (2008) 460-465. [40] Y. Teraoka, H.-M. Zhang, S. Furukawa, N. Yamazoe, Oxygen permeation through perovskite-type oxides, Chemistry Letters 14 (1985) 1743. [41] G.Z. Cao, Electrical conductivity and oxygen semipermeability of terbia and yttria stabilized zirconia, Journal of Applied Electrochemistry, 24 (1994) 1222-1227. [42] H.J.M. Bouwmeester, H. Kruidhof, A.J. Burggraaf, P.J. Gellings, Oxygen semipermeability of erbia-stabilized bismuth oxide, Solid State Ionics, 53-56 (1992) 460-468. [43] Y.-S. Lin, W. Wang, J. Han, Oxygen permeation through thin mixed-conducting solid oxide membranes, AIChE Journal, 40 (1994) 786-798. [44] L.M. van der Haar, H. Verweij, Homogeneous porous perovskite supports for thin dense oxygen separation membranes, Journal of Membrane Science, 180 (2000) 147-155. 22

[45] B.C.H. Steele, Oxygen ion conductors and their technological applications, Materials Science and Engineering: B, 13 (1992) 79-87. [46] H.J.M. Bouwmeester, Dense ceramic membranes for methane conversion, Catalysis Today, 82 (2003) 141-150. [47] G.B. Balazs, R.S. Glass, AC impedance studies of rare earth oxide doped ceria, Solid State Ionics, 76 (1995) 155-162. [48] Z. Zhan, T.-L. Wen, H. Tu, Z.-Y. Lu AC impedance investigation of samarium-doped ceria, Journal of The Electrochemical Society, 148 (2001) A427-A432. [49] W. Huang, P. Shuk, M. Greenblatt, Properties of sol-gel prepared Ce1−xSmxO2−x solid electrolytes, Solid State Ionics, 100 (1997) 23-27. [50] W. Huang, P. Shuk, M. Greenblatt, Hydrothermal synthesis and properties of Ce1-xSmxO2-x and Ce1-xCaxO2-x solid solutions, Chemistry of Materials, 9 (1997) 2240-2245. [51] Y. Fu, S. Li, Y. Jiang, Analysis of inter-laminar stresses for composite laminated plate with interfacial damage, Acta Mechanica Solida Sinica, 21 (2008) 127-140. [52] H. Kruidhof, H.J.M. Bouwmeester, R.H.E.V. Doorn, A.J. Burggraaf, Influence of orderdisorder transitions on oxygen permeability through selected nonstoichiometric perovskite-type oxides, Solid State Ionics, 63–65 (1993) 816-822. [53] L. Qiu, T.H. Lee, L.M. Liu, Y.L. Yang, A.J. Jacobson, Oxygen permeation studies of SrCo0.8Fe0.2O3−δ, Solid State Ionics, 76 (1995) 321-329. [54] A. Thursfield, I.S. Metcalfe, The use of dense mixed ionic and electronic conducting membranes for chemical production, Journal of Materials Chemistry, 14 (2004) 2475-2485.

23

Highlights



Dense highly stable dual-phase ceramic composite membranes were fabricated at 1400oC.



Ca- and Co-doped yttrium chromite provided excellent electronic conductivity.



Samaria-doped ceria provided high ionic conductivity and phase stability.



O2 permeation characteristics are adequate for O2 separation.



Ceramic membranes are suggested for use in sustainable fuel production and power generation.

24

Dual-Phase Ceramic Composite Membrane Air

Yttrium Chromite Ceria 2 m

O2

25