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Journal of the American Ceramic Society, 90, 5, 2007
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Fabrication of gas electrodes by wet powder spraying of binder-free
particle suspensions using a pulse injection process
Oishi, Naoki; Yoo, Yeong; Davidson, Isobel
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Fabrication of Gas Electrodes by Wet Powder Spraying of Binder-Free
Particle Suspensions Using a Pulse Injection Process
Naoki Oishi,
wYeong Yoo, and Isobel Davidson
Institute for Chemical Process and Environmental Technology, National Research Council Canada, Ottawa, Ontario, Canada
A process for wet powder spraying of binder-free particle sus-pensions using pulse injection was devised for the fabrication of gas electrodes. The resulting deposited electrodes were found to have fine and uniformly distributed pores, to have good adhe-sion, and low interfacial resistance on electrolyte substrates. The uniformity of the layers was improved by decreasing the spray pulse to 0.05 s with a 1-s off period. Even without drying or any pre-treatments before firing, there was no cracking or delami-nation of the deposited layer. The deposited layer remained porous, crack-free, and well bound to the substrate after firing.
I. Introduction
I
Nsolid-state ionic devices such as solid oxide fuel cells and gassensors, the porous gas electrode plays a key role in the col-lection of electric power, and electrochemical potential from the triple-phase boundary region at the interface of the electrolyte, electrode, and gas phase.
For the fabrication of gas electrodes, different techniques can be used to achieve desired homogeneous functional layers with a well-defined thickness on substrates, and the screen-printing process is a widely used technique that uses a paste containing the electrode material in solid-oxide fuel cells.1,2 The screen-printing paste needs to be prepared such that the printed layer will have a homogeneous distribution of the mixed phases with controlled thickness and adequate adhesion to the substrate. In the screen-printing process, porosity is created by burning off polymeric agents that are added to the electrode paste.
In order to fulfill the requirements for the paste, organic components of binder, plasticizer, and dispersant have com-monly been used. The screen-printing paste is prepared consid-ering the relationship between the added agents and the resulting properties of the paste. The formulation of a paste depends on accumulated technical know-how and affects the formation of porosity, which is associated with the performance of a porous gas electrode. In general, processes for removing solvents and polymeric agents are relatively slow.
From the view-point of controllability of a printed structure, inkjet printing, which is being used for free-forming of solid ce-ramic objects,3,4is expected to have the potential to fabricate a gas electrode more precisely. Inks for inkjet printing are also composed of a variety of polymeric agents. Like screen-printing pastes, there are several variables for selecting and mixing additives to adjust the properties of the ink for viscosity, sur-face tension, and density, which can affect the resulting printed structures. Consequently, the ink for inkjet printing is also a complex system requiring a variety of experiments to specify a certain formula. Much like screen printing, the drying and firing
processes for fabrication of gas electrodes by inkjet printing will require considerable time and care.
In solid-oxide fuel cells, the concept of using a metallic sup-port has attracted attention in terms of cells’ mechanical and thermal characteristics and its cost, recently an intermediate op-eration using ferritic stainless-steel supports, was demonstrated by a U.K. company.5The resistance of stainless steel to oxidiz-ing environments is achieved by the chromium content, while chromium’s higher affinity for carbon and low solubility of car-bon in ferritic stainless-steel leads to the a formation of brittle chromium carbide phases at grain boundaries in carbon-con-taining atmospheres (intergranular corrosion).6,7 The metallic support plays an important role not only as a mechanical sup-port but also as a current collector; therefore, the process deal-ing with ferritic stainless steels needs to be carefully conducted to confer a structurally stable surface to the electrode. Accordingly, for metal-supported types, processing technologies capable of fabricating electrodes using less polymeric agents (less carbon) in a shorter time would be more preferable because it would help to reduce the risks associated with the carbide formation and to keep the oxidation of metal supports to a minimum during a series of processings.
Wet powder spraying has the potential to fulfill these require-ments; it has been used as a processing technique to form porous gas electrodes.8–11A powder suspension is sprayed with a nozzle that forms droplets in a carrier gas flow. This process does not require as much binder as screen printing. As opposed to the screen printing; the wet powder spraying is a non-contact tech-nique like inkjet printing, this techtech-nique is more suitable for en-gineering structures, i.e., functionally graded electrodes, and is applicable to a variety of surfaces, corrugated sheets, and tubes. However, it is necessary to take the velocity of droplets into ac-count because this could disturb the formation of sprayed layers. In general, the distance between the nozzle and the surface being sprayed should be long enough to avoid disturbing the deposited material.
Binder-free suspensions can easily be vaporized to produce solid porous layers by a spraying procedure. Reproducibility in the viscosity of the suspension can be achieved by adjusting the solid content. The lower the viscosity of a suspension, the lower the carrier gas pressure required for spraying, which then leads to a decrease in the velocity of droplets that in turn can alleviate the impact of droplets on the layers being deposited. However, in the case of wet powder spraying with a binder-free suspen-sion, there may be a problem with adhesion between the sprayed layer and the substrate.
The smaller the particle size in the suspension becomes, the stronger the agglomeration between particles in the sprayed layer will be. If the suspension is composed of very fine parti-cles, it is expected that the sprayed particles will be able to adhere strongly to the surface being sprayed.
In this study, wet powder spraying using a binder-free powder suspension composed of very fine particles that was prepared in a simple single step was investigated for fabrication of porous gas electrodes; particularly, in order to minimize the detrimental influence of fast droplet velocity on the formation of a sprayed
R. Cutler—contributing editor
w
Author to whom correspondence should be addressed. e-mail: oishin@nrc.ca Manuscript No. 21254. Received December 15, 2005; approved March 1, 2006.
Journal
DOI: 10.1111/j.1551-2916.2006.01425.x r2006 The American Ceramic Society
layer bonded to the substrate, a sequence of spray was devised for the injection of the suspension to be made in an intermittent pulse mode of several tens of milliseconds. For this investiga-tion, strontium-doped lanthanum cobaltite, which has been of interest for intermediate temperature solid oxide fuel cells,12,13 was selected as the electrode material, and was sprayed onto flat-sintered-doped cerium oxide substrates. The feasibility of this processing for gas electrodes was examined.
II. Experimental Procedure
(1) Preparation and Characterization of a Binder-Free, Fine-Particle Suspension of La0.5Sr0.5CoO3
As-received La0.5Sr0.5CoO3powder (99.9%, d505 0.9 mm, Prax-air, Woodinville, WA) was heat treated under a continuous flow of molecular-sieved air at 5001C for 3 h to burn out organic residues and absorbed inorganic species. For the suspension medium, ethanol (anhydrous, Commercial Alcohols Inc., Tor-onto, Canada) was chosen, and was dried with molecular sieves (3A, Sigma-Aldrich, Oakville, Canada) before use.
1.5 g of the heat-treated powder was placed in a 60 mL poly-propylene container with 50 g of zirconia grinding media (1 mm YTZsball, Tosoh, Tokyo, Japan), and then 15 g of the dried ethanol was added. No further additives such as binders, plas-ticizers, or dispersants were used. The mixture of La0.5Sr0.5CoO3 powder and ethanol was agitated on a high-energy milling ma-chine (8000M, SPEX CertiPrep Inc., Metuchen, NJ) with a clamp speed of 1060 rpm and a clamp’s swing-amplitude of about 20 mm. To avoid rapid heating of the ethanol medium in the container during the milling, the high-energy milling was conducted in a cyclic sequence of a 60-s on period for milling and a 240-s off period for cooling. The accumulated time for milling was set to be 300 s.
After milling, additional ethanol was added to the milled sus-pension of La0.5Sr0.5CoO3to increase the total amount of eth-anol to 50 g, and consequently, the powder concentration in the diluted suspension was 3 wt% at most. A sedimentation test using a 20-mL test tube with a filling height of 50 mm was per-formed to examine the stability of the suspension, and the par-ticle size distribution of the milled powder was measured by a particle size analyzer (Zetasizer 2000, Malvern, Malvern, U.K.). A thermo gravimetrical analysis of the milled La0.5Sr0.5CoO3 powder was carried out to measure the level of contamination from the polypropylene container.
(2) Spraying Process and Subsequent Firing Process A commercially available 0.3 mm fluid nozzle airbrush with a double action function for fluid and carrier gas control was modified by attaching a solenoid coil to control the needle for loading of a fluid suspension. The solenoid coil was controlled by a time-delayed relay capable of switching on and off at rates as fast as 0.01 s. Nitrogen was used as the carrier gas at a work-ing pressure of 0.7 bar, which resulted in a flow rate of about 90 cm3/s during spraying.
The spray nozzle was aligned vertically to the substrate, which was located below the spray apparatus, leaving a 100 mm distance between them. The substrate was a sintered Ce0.8Sm0.2O2disk (13 mm in diameter, 1 mm in thickness) pol-ished with # 600 abrasive papers and cleaned by ethanol. In order to spray the suspension, the carrier gas was allowed to flow continuously onto the Ce0.8Sm0.2O2 substrate, while the solenoid coil was intermittently activated by the relay for on-time periods, ton, of 0.05, 0.1, 0.5, or 1 s with a subsequent off-time period, toff, of 1 s until all of the desired amount of suspension had been sprayed. Schematic diagrams of the cross-sectional view of the nozzle, the arrangement, and the spray sequence are shown in Fig. 1. The spraying process was carried out at room temperature under atmospheric pressure.
After spraying, samples were simply fired at 9001C for 3 h in air without any pre-treating stages before firing. The heating and cooling rates were set to be 6001C/h.
(3) Characterization of the Porous Gas Electrodes
The surface morphology of the La0.5Sr0.5CoO3layers was ana-lyzed with a scanning confocal microscope (Sensofar, Solarius Development Inc., Sunnyvale, CA). The microstructural analy-sis was carried out on a field emission-type scanning electron microscope (SEM; S-4800, Hitachi, Tokyo, Japan) equipped with an energy-dispersive X-ray spectroscope (EDS; INCAx-sight & INCAx-stream, Oxford Instruments, Eynsham, U.K.). AC impedance measurements were conducted in air on sym-metrical cells of La0.5Sr0.5CoO3|Ce0.8Sm0.2O2|La0.5Sr0.5CoO3 with an impedance/gain-phase analyzer (1260, Solartron, Farn-borough, U.K.) and an electrochemical interface (1287, Solart-ron, U.K.) over the frequency range from 105to 10 3Hz with an AC amplitude of 10 mV.
III. Results and Discussion
Regarding the filling height of the milled suspension of 50 mm, there was no transparent supernatant observed during the test period of over 90 h, indicating that the suspension prepared without any chemical additives was very stable. It should be noted that although there was no transparent supernatant ob-served over the sedimentation test period, some particles from the colloidal suspension settled to the bottom. As can be seen in Fig. 2, the mean particle size was found to be around 0.23 mm with a sharp bimodal distribution.
Contamination of polypropylene from the milling container, which might affect the firing process, was estimated to be less than 2 wt% by thermo-gravimetrical analysis. Accordingly, the magnitude of polypropylene contamination during milling was not significant. 10 0 30 15 in mm t Fluid channel 15 m 15 15 On Off Off ton off Solenoid Carrier gas On time
Carrier gas channel
To solenoid coil
Needle oscillation (adjustable) Close Open Airbrush body Needle Not to scale Nozzle Sample holder Spray area
Fig. 1. Schematic diagrams of a cross-sectional view of an airbrush at-tached with a solenoid coil (bottom), an arrangement (top right), and a sequence for spray (top left).
Fluid loading per one-shot spray over a tonrange of 0.05–0.5 s was examined for a range of needle oscillation amplitudes. Over the range tested, the fluid loading per one shot was found to increase proportionally to tonas can be seen in Fig. 3. The amp-litude of the needle movement activated by the solenoid coil could also change the fluid loading; however, it was adjusted such that a tonof 0.05 s would provide 4–5 mL of fluid per shot during the spraying of the suspension.
Photo images of La0.5Sr0.5CoO3layers sprayed at different ton times onto Ce0.8Sm0.2O2substrates taken with an image scanner are shown in Fig. 4. These samples were fired at 9001C to fix the layer onto the substrate before the scanning. The black areas indicate coated surfaces, while the gray areas indicate the Ce0.8Sm0.2O2 substrate surfaces. The spray conditions within the tonperiods studied appeared to provide sprayed layers free of delamination from the surface. For depositions made at ton periods of 0.5 and 1.0 s, there is a large uncoated area and the coated layer is patchy and wavy. For the deposition at a tonof 0.1 s, most of the layer appears to be uniform; however, there is a patchy area around the center. In contrast, the layer sprayed with a tonof 0.05 s is found to be evenly coated with the sprayed powders over the entire Ce0.8Sm0.2O2surface. As tondecreased from 1.0 to 0.05 s, the uniformity of the sprayed La0.5Sr0.5CoO3 layer was improved on a macroscopic scale.
Three-dimensional surface profiles of the area of 640 mm 480 mm for ton5 0.05 and 0.1 s are shown in Fig. 5. It is apparent that the spraying condition with a shorter on-time period gives better uniformity to the surface. At a tonof 0.05 s (4–5 mL per shot) and a toffof 1 s, layers over 30 mm in thickness were reproducibly obtained, and the film thickness per suspen-sion (suspensuspen-sion consumption efficiency) was found to be around 3 mm/mL, which was found to be more efficient than the continuous spray mode with a longer distance. In the other
electrode materials we tested,14suspensions with a single sharp particle distribution were also found to produce uniform elec-trode material layers without delamination under a similar spraying condition; the effect of the bimodal distribution seen in this study remained unknown. It should be noted that con-tinuous spraying (normal spraying) could not produce coated layers on the substrate under the same conditions of 0.7 bar in working pressure and 100 mm in distance.
A model for the building up of the deposited layer during spraying is proposed as follows: as soon as the droplets arrive at the substrate surface, the liquid phase surrounding powder par-ticles starts to vaporize. During the subsequent off-time period of 1 s, the continuous flow of the carrier gas (at a velocity of about 13 cm/s at the sample holder) accelerates the vaporization of ethanol, leaving powder particles to agglomerate consequent-ly on the substrate surface. The subsequent droplets deposited after an off-time period arrive at particles already adhered to the surface. Not only the continuous gas flow but also the porous structure being built up by the agglomerated particles under-neath can facilitate the vaporization of the liquid phase because the liquid phase can also be adsorbed by the porous structure by capillary force. The net result is an increase in the exposed sur-face area for fast vaporization. Accordingly, the sprayed struc-ture is built up layer by layer with agglomerated particles.
When the on-time period is longer (ton40.5 s), the subsequent off-time period is not long enough to ensure the completion
50 0 40 30 20 10 101 102 103 104 Diameter (nm) Volume (%)
Fig. 2. Particle distribution of a La0.5Sr0.5CoO3–ethanol suspension
milled for 300 s. 60 0 40 30 20 10 0 0.2 0.4 On time period ton(s) Fluid loading (µl) 50 0.5 0.3 0.1 0.6
Fig. 3. Fluid loading per one shot as a function of on-time period ton
for different needle oscillation amplitudes ( & omo
in arbitrary unit).13 mm
t
on= 0.05
t
on= 0.1
t
on= 0.5
t
on= 1
Fig. 4. Scanned photo images of La0.5Sr0.5CoO3layers made with
of the vaporization. Thus, particles can flow in the liquid phase on the substrate surface due to the force of the carrier gas flow, resulting in a wavy morphology and a patchy sprayed layer.
Increasing the distance between the nozzle and the substrate can improve the quality of the sprayed layer; however, it results in a longer spray-processing time being required to reach a
desired thickness. Based on the results of the effects of the on-time period, it is expected that if fluid loading per shot could be reduced further, then the distance between the nozzle and the substrate could be made closer, which should lead to faster processing.
After firing the deposited samples at 9001C for 3 h in air, there was no macroscopic evidence of cracking or delamination ob-served in the sprayed layers. A simple adhesion test using scotch tape was conducted. It was found that the scotch tape could not remove a significant amount of material from a fired layer de-posited on the surface of the Ce0.8Sm0.2O2substrate having a thickness of 5–7 mm. The SEM micrographs of a top-surface and a cross-sectional view of a fractured surface of a La0.5Sr0.5CoO3 layer deposited on Ce0.8Sm0.2O2 are shown in Fig. 6. The La0.5Sr0.5CoO3layer is porous and the pores are evenly distrib-uted throughout the area. Although La0.5Sr0.5CoO3has a ther-mal expansion coefficient ( 23 10 6K 1) that is almost two times greater than that of Ce0.8Sm0.2O2( 12 10
6
K 1),15,16
the temperature ranges for which the thermal expansion coeffi-cient were taken, the porous layer was found to remain well adhered.
In order to address the possibility of contamination of the deposits with zirconia from the grinding media, an elemental analysis by EDS was conducted. The levels of zirconium and yttrium in the fired La0.5Sr0.5CoO3layer were less than the de-tection limit (B0.1%). It is well known that lanthanum cobal-tites doped with strontium like La0.5Sr0.5CoO3 can react with zirconium17,18at high temperatures to form highly electrically resistive La2Zr2O7and SrZrO3phases. As can be seen in Fig. 7, comparing the interfacial resistance of La0.5Sr0.5CoO3 on Ce0.8Sm0.2O2with a number of reference data,13,19,20the inter-facial resistance was found to be low and similar to other co-baltites. It was, therefore, thought that the contamination from zirconia during the milling process was negligibly low and did not significantly affect the interfacial resistance between the porous electrode and the electrolyte substrate.
Using this pulse injection spray technique, it was found that the uniformity of the sprayed layer was improved by shortening the pulses for the injection of the suspension into the spray noz-zle. In this process, the sprayed layer was actually dried during each off period in the spraying process, and consequently, there was no need to dry the sprayed layer before the firing process. As the deposited layer did not contain any polymeric agents, the firing process did not require a pyrolysis stage. The layer was built up by the agglomeration of the sprayed particles, and con-sequently, without using any polymeric agents, a porous struc-tured layer remained after firing. The wet powder spraying using a pulse injection process is a simple system; hence, it is thought
480 µm 640 µm µm 4 3.5 3 2 1 0 2.5 1.5 0.5 µm 4 3.5 3 2 1 0 2.5 1.5 0.5
Fig. 5. Three-dimensional surface profiles (640 mm 480 mm) of La0.5Sr0.5CoO3layers made at tonperiods of 0.05 s (top) and 0.1 s
(bot-tom).
Fig. 6. Scanning electron micrographs of a La0.5Sr0.5CoO3layer fired at
9001C in air for 3 h; top surface (top) and fractured surface (bottom).
102 10−2 101 100 10−1 0.8 1.0 1.2 1.6 1000/T (K−1) Interfacial resistance ( Ω cm 2) 1.4 This work La0.6Sr0.4CoO3 [13] Sm0.5Sr0.5CoO3 [19] Gd0.5Sr0.5CoO3 [20]
Fig. 7. Temperature dependence of interfacial resistance of La0.5Sr
0.5-CoO3on Ce0.8Sm0.2O2in air with reference data.
to be scalable for a large area in combination with a three-axis manipulating system.
IV. Conclusions
In order to simplify the fabrication process for gas electrodes on electrolyte substrates, a wet powder spraying process was de-vised to apply a pulse injection of a binder-free suspension com-posed of very fine particles. The suspension was prepared in a simple single step using high-energy ball milling. It was found that the quality of a spray-deposited layer was improved by re-ducing the duration of the spray pulses to 0.05 s with a 1-s off period between pulses. Even without any drying or any pre-treatments before firing, there was no cracking or delamination of the spray-deposited layers after firing. Furthermore, the sin-tered layer remained porous as is required for use as a gas elec-trode. The contaminations from polypropylene container and zirconia grinding media were found to be negligible and did not affect either the firing stage or the interfacial resistance between the porous electrode and the electrolyte substrate, respectively.
References
1
G. M. Christie and J. P. P. Huijsmans, ‘‘State of the Art SOFC Component Development at ECN’’; pp. 718–26 in SOFC V. PV 97-40, Edited by U. Stimming, S. C. Singhal, H. Tagawa, and W. Lehnert. The Electrochemical Society, Pennington, NJ, 1997.
2
D. Ghosh, G. Wang, R. Brule, E. Tang, and P. Huang, ‘‘Performance of Anode Supported Planar SOFC Cells’’; pp. 822–9 in SOFC VI. PV 99-19, Edited by S. C. Singhal and M. Dokiya. The Electrochemical Society, Pennington, NJ, 1999.
3
M. Mott, J.-H. Song, and J. R. G. Evans, ‘‘Microengineering of Ceramics by Direct Ink-Jet Printing,’’ J. Am. Ceram. Soc., 82, 1653–8 (1999).
4
P. F. Blazdell and J. R. G. Evans, ‘‘Application of a Continuous Ink Jet Printer to Solid Freeforming of Ceramics,’’ J. Mater. Process. Technol., 99, 94–102 (2000).
5
P. Bance, N. P. Brandon, B. Girvan, P. Holbeche, S. O’dea, and B. C. H. Steele, ‘‘Spinning-Out a Fuel Cell Company from a UK University —2 Years of Progress at Ceres Power,’’ J. Power Sources, 131, 86–90 (2004).
6
R. P. Frankenthal and H. W. Pickering, ‘‘Intergranular Corrosion of a Ferrtic Stainless Steel: A Critical Test of the Chromium-Depletion Theory,’’ Corrosion, 28, 466 (1972).
7
J. J. Demo and A. P. Bond, ‘‘Intergranular Corrosion and Embrittlement of Ferrtic Stainless Steels,’’ Corrosion, 31, 21–2 (1975).
8
K. Wippermann, U. Stimming, H. Jansen, and D. Stover, ‘‘Electrochemical Behavior of Perovskite Cathodes Made by Wet Powder Spraying’’; pp. 180–9 in SOFC III. PV 93-4, Edited by S. C. Singhal and H. Iwahara. The Electrochemical Society, Pennington, NJ, 1993.
9
N. M. Sammes, M. S. Brown, and R. Ratnaraj, ‘‘Wet Powder Spraying of a Cermet Anode for a Planar Solid Oxide Fuel Cell System,’’ J. Mater. Sci. Lett., 13, 1124–6 (1994).
10
R. Wilkenhoner, W. Mallener, H. P. Buchkremer, T. Hauber, and U. Stimm-ing, ‘‘Cathode Processing by Wet Powder Spraying’’; pp. 279–88 in Second Euro-pean Solid Oxide Fuel Cell Forum, Edited by B. Thorstensen. EuroEuro-pean SOFC Forum, Oberrohrdorf, Switzerland, 1996.
11
V. Dusastre and J. A. Kilner, ‘‘Optimisation of Composite Cathodes for Intermediate Temperature SOFC Applications,’’ Solid State Ion., 126, 163–74 (1999).
12
T. Ishihara, T. Shibayama, H. Arikawa, M. Honda, H. Nishiguchi, and Y. Takita, ‘‘Intermediate Temperature Solid Oxide Fuel Cell Using Ni Doped LaGaO3Electrolyte’’; pp. 869–78 in SOFC VI. PV99-19, Edited by S. C. Singhal
and M. Dokiya. The Electrochemical Society, Pennington, NJ, USA, 1999.
13
M. Shiono, K. Kobayashi, T. L. Nguyen, K. Hosoda, T. Kato, K. Ota, and M. Dokiya, ‘‘Effect of CeO2Interlayer on ZrO2Electrolyte/La(Sr)CoO3Cathode
for Low-Temperature SOFCs,’’ Solid State Ion., 170, 1–7 (2004).
14
N. Oishi, Y. Yeong, and I. Davidson, ‘‘La0.6Sr0.4Co0.2Fe0.8O3–Ce0.8Sm0.2O2-d
Composite Cathode for Operation below 6001C’’; pp. 1645–51 in SOFC IX. PV2005-07, Edited by S. C. Singhal and J. Mizusaki. The Electrochemical Soci-ety Inc., Pennington, NJ, 2005.
15
N. Q. Minh, ‘‘Ceramic Fuel Cells,’’ J. Am. Ceram. Soc., 76, 563–88 (1993).
16
B. C. H. Steele, ‘‘Oxygen Transport and Exchange in Oxide Ceramics,’’ J. Power Sources, 49, 1–14 (1994).
17
O. Yamamoto, Y. Takeda, R. Kanno, and M. Noda, ‘‘Perovskite-Type Ox-ides as Oxygen Electrodes for High Temperature Oxide Fuel Cells,’’ Solid State Ion., 22, 241–6 (1987).
18
E. Ivers-Tiffee, M. Schiessl, H. J. Oel, and W. Wersing, ‘‘Investigation of Cobalt-Containing Provskites in SOFC Single Cells with Respect to Interface Re-actions and Cell Performance’’; pp. 613–22 in SOFC III. PV 93-4, Edited by S. C. Singhal and H. Iwahara. The Electrochemical Society, Pennington, NJ, 1993.
19
C. Xia, W. Rauch, F. Chen, and M. Liu, ‘‘Sm0.5Sr0.5CoO3Cathodes for
Low-Temperature SOFCs,’’ Solid State Ion., 149, 11–9 (2002).
20
C. Rossignol, J. M. Ralph, J.-M. Bae, and J. T. Vaughey, ‘‘Ln1 x
SrxCoO3(Ln 5 Gd, Pr) as a Cathode for Intermediate-Temperature Solid Oxide
