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Layered Ruddlesden-Popper La2NiO4+δ (LNO) is reported to possess excellent oxygen surface and bulk transport properties, but its application as the cathode of solid oxide fuel cells is restrained by the relatively poor electrocatalytic activity. Here, we report the incorporation of highly ion-conducting Er-stabilized Bi2O3 (ESB) into LNO and assemble the LNO-ESB composite cathode directly on zirconia electrolyte film using a facile electrochemical polarization approach. The results show the presence of ESB remarkably reduces the contact resistance at the electrode/electrolyte interface and enhances the electrocatalytic activity and cation stability of LNO. The cell with the LNO-ESB cathode generates a peak power density of 852 mW cm-2 at 750°C with reasonable operating stability over 200 h. This work demonstrates the feasibility of incorporating ESB to promote the layered nickelate cathodes for intermediate temperature solid oxide fuel cells. Published version

Inorganic-organic nanostructured hybrid membranes of polyethersuflone (PES)-polyvinylpyrrolidone (PVP) were prepared with mesoporous silica materials. Hollow mesoporous silica is synthesized via cationic surface-assistant etching method, while amino-functionalized hollow mesoporous silica and amino-functionalized mesoporous silica spheres were synthesized via post-grafting strategy. After the addition of mesoporous silica and amino-functionalized mesoporous silica into the matrix of PA doped PES-PVP composite membranes, all composite membranes show similar PA uptake. However, the proton conductivity of the composite membranes increases significantly with the substantial decrease in the activation energy for proton diffusion, especially for the amino-functionalized hollow mesoporous silica material. That reason is most likely due to the facilitated proton transportation in the ordered mesoporous channels via the hydrogen bond between the –NH2 groups and H3PO4. Cell performance also confirms the superiority of the addition of inorganic fillers in PES-PVP membrane, and the highest peak power density at 180 oC was 480 mW cm-2 for NH2-HMS based composite membrane, which is 92.7 % higher than that of PA doped PES-PVP composite membrane at the identical condition. The results show promising application of NH2-HMS based PES-PVP composite membrane for elevated temperature proton exchange membrane fuel cells. Figure 1

Performance degradation of cathodes due to the attack by chromium from Fe-Cr alloy interconnect is a major barrier to develop long-term durable solid oxide fuel cells (SOFCs). In this presentation, we report the development of a chromium tolerant BaO infiltrated La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode. After the test at 800oC for 100 h in the presence of Fe-Cr interconnect, the electrode polarization resistance (RE ) of the infiltrated BaO-LSCF electrode increases by 0.05 Ω cm2, much smaller than 0.48 Ω cm2 in the case of the LSCF electrode. The presence of BaO nanoparticles inhibits the formation of SrCrO4 by forming thermodynamically stable and conducive BaCrO4, thus preventing the extraction of Sr at the A-site of LSCF perovskite structure and mitigating the poisoning effect of Cr on the electrocatalytic activity of LSCF. The results have demonstrated a new and effective strategy to develop highly tolerant and resistant cathodes towards the Cr contaminant of SOFCs.

Ni/Y2O3 stabilized ZrO2 (Ni/YSZ) cermet is a widely used hydrogen electrode for solid oxide fuel cells (SOECs), but detailed studies regarding the water splitting processes are scarce. Here we report the preliminary results on the variation of electrocatalytic activity of Ni/YSZ hydrogen electrodes as a function of operating temperature, water concentration and dc bias. The electrode activity for the water splitting reaction is strongly influenced by varying the water concentration and dc bias. The electrochemical performance for the water splitting reaction decreases with the increase of water concentration. The electrode polarization resistance increases gradually with the increase of dc bias regardless of the H2O content. The decrease of activity is particularly pronounced in the low frequency impedance process related to the H2O dissociative adsorption and diffusion processes. This study clearly demonstrates the reaction mechanism and kinetics of the H2O dissociation reaction.

The effect of volatile boron species on the electrocatalytic activity, microstructure and phase stability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathodes has been studied. The cathodes were heat-treated at 800C for 7 days in air in the presence of boron species vaporized from borosilicate glass, and were characterized by EIS, SEM, AFM, SIMS, XRD, XPS and ICP-OES. The results have shown that after the heat-treatment in the presence of borosilicate glass, boron deposition occurs mainly on the region near electrode surface, leading to the significant Ba and in particular Sr segregation, microstructure change and phase decomposition. On the other hand, the microstructure of the inner electrode layer is almost intact. Electrode polarization resistance, RE, of an as-prepared BSCF cathode is 0.93 and 0.23 Ω cm at 650 and 800 C, respectively, and changes to 2.08 and 0.15 Ω cm after ∗ Corresponding author. Tel.: +61 8 9266 9804; fax: +61 8 9266 1138. Email address: s.jiang@curtin.edu.au (S.P. Jiang).

As a mixed electronic and ionic conductor (MIEC), (La,Sr)FeO3-δ has been extensively studied to replace manganite based materials as oxygen electrode of intermediate temperature (600-800oC) reversible solid oxide cells (RSOCs). However, compared to Sr doped LaCoO3 material, the electrochemical performance of cobalt-free (La,Sr)FeO3-δ needs to be improved to meet the requirements of commercial applications. Contrary to the conventional solid-state reaction and sol-gel method, molten salt synthesis (MSS) is a simple, versatile, and environmental-friendly approach to synthesize highly active perovskite catalysts with controllable compositions and morphologies. Especially, the corrosion effect of molten salts and the salt-removal process in MSS process have potential to manufacture particles with open porous topographic structure, resulting in large specific surface area. Therefore, it’s promising to use the MSS method to enhance the activity of cobalt-free (La,Sr)FeO3-δ. In this study, the MSS method was employed to synthesize perovskite La0.6Sr0.4FeO3-δ (LSF) at 850oC as the oxygen electrode of a button solid oxide cell. In the material preparation procedure, moderate chloride composite was added in the reactants, forming a liquid environment to accelerate the reaction. At 800 °C, the button cell exhibits a peak power density of 1.73 Wcm-2 using pure H2 as fuel and reaches an electrolysis current density of 1.50 Acm-2 under 1.3 V in 50% CO2/50% H2, both of which are much better than the reference cell with a La0.6Sr0.4FeO3-δ electrode prepared by sol-gel method. The button cell also demonstrates a stable performance under a constant current density of 0.5 Acm-2 in SOFC mode for 200 hours. We also discussed the mechanism for the ultra-high electrochemical performance of La0.6Sr0.4FeO3-δ by charactering the difference between LSF powders synthesized by MSS method and sol-gel method. The results show that LSF using MSS powders possess a great plenty of pores in the grains. Meanwhile, the valance and the coordinator number of Fe atoms are reduced owing to the poor solubility of oxygen and the corrosion in the molten chlorides, leading to more oxygen vacancies. Therefore, we concluded that the combining effect of the microstructure and the enhanced amount of oxygen vacancies make the porous LSF electrode exhibits attractive electrochemical performance in both SOFC mode and SOEC mode. Figure 1

Effect of volatile boron species on the properties of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode materials has been studied in detail by using porous electrode coatings and dense bar samples. Prior to the characterization, the LSCF samples were heat-treated at 800oC in air in the presence of borosilicate glass for 7 and 30 days. Heat-treatment in the presence of glass has a significant detrimental effect on the surface exchange rate, electrical properties, and electrochemical activity of the cathodes. Secondary ion mass spectroscopy (SIMS) detected the deposition of boron as well as sodium and potassium on the surface and in the bulk of the bar samples. The boron deposition results in significant microstructure and composition changes. Sr in the form of SrB2O4 is enriched on the outmost surface of LSCF bar samples, leading to the Sr-deficient in the adjacent layer in the bulk. The present study demonstrates the remarkable detrimental effect of volatile boron species on the microstructure and electrochemical activity degradation of the LSCF cathode materials of solid oxide fuel cells.

Oxygen electrode is a key component for solid oxide electrolysis cells (SOECs). Double perovksite oxide SmBaCo2O5+ d (SBCO) exhibits both high electrical conductivity and fast oxygen transport properties, herein we proposed SBCO as a novel high efficient SOEC oxygen electrode based on Ce0.9Gd0.1O1.9 (GDC) electrolyte. Preliminary study showed that an area specific resistance 0.024 W cm2 was achieved under OCV condition at 900°C and a stable operation of 20h was performed at an anodic polarization current density of 200mA×cm-2.

Cinairinthepresenceofborosilicateglassfor7and30days.SIMSdetectedthedepositionofboron as well as sodium and potassium on the surface and in the bulk of the bar samples. The boron deposition results in significantmicrostructure and composition changes. SIMS, EDS and XRD confirm that Sr in the form of SrB

The relationship between the surface segregation, boron poisoning and surface exchange coefficients of La0.6Sr0.4Co0.2Fe0.8O3−δ, (LSCF) cathodes of solid oxide fuel cells (SOFCs) is studied on dense bar samples using SEM, SIMS and conductivity relaxation method. The SEM results clearly indicate that the segregation on the LSCF surface occurs after heat-treatment at 700‐800 ◦ C for 48h, forming isolated particles on the LSCF surface. The presence of volatile boron species accelerates grain growth of the segregated particles and reacts with LSCF. The depth of boron reaction layer after heat-treatment in the presence of E-glass at 700 ◦ C, 750 ◦ C and 800 ◦ C for 48 h was 2, 5 and 40 nm, respectively. The depth profiles analysis of SIMS indicates that there is segregation and enrichment of constituent elements of LSCF on the electrode surface, in line with the depth profile of boron species on the LSCF sample surface layer. Boron deposition and poisoning deteriorates the surface exchange and diffusion processes for the oxygen reduction reaction on LSCF. After exposed to boron at 800 ◦ C for 48 h, the surface exchange coefficient, Kchem is 6.0 × 10 −5 cm s −1 , more than one magnitude lower than 1.1 × 10 −3 cm s −1 of as-prepared LSCF samples.

In this paper, four fuel cells were prepared using anode supported YSZ electrolyte membranes with different thickness by slurry spin coating technique and tested at 700{degree sign} C to 800{degree sign}C. By fitting the AC impedance spectra of fuel cells, the ohmic and electrochemical polarization resistances were distinguished. It has been found that the directly calculated conductivity and activation energy data of ohmic resistance based on impedance spectra measurement are much lower than that from bulk electrolyte. This phenomenon is discussed by analyzing the ohmic resistance data of four fuel cells with different membrane thickness. According to the analysis, an approach for measuring the conductivity of electrolyte membrane was developed to improve the calculation accuracy by fitting the ohmic area specific resistances to thicknesses of membrane, at the same time, it also can be used to evaluate the resistance contribution of anode supporter, cathode and current collector.

Solid oxide cells (SOCs) are high-temperature electrochemical energy conversion and storage devices, which can be operated under solid oxide electrolysis cell (SOEC) mode to produce pure hydrogen from water vapor with high efficiency. SOCs can also be operated in reverse under solid oxide fuel cell (SOFC) mode, providing high-energy conversion efficiency to convert hydrogen fuel to electricity. Similar to SOFCs, cost-effective metallic (alloy) can be used as interconnects for planar-type SOCs operated at reduced temperatures (≤ 800 °C). However, without an effective protective coating on the Cr-containing alloy, volatile Cr-containing species are generated at high temperatures in oxidizing atmosphere. It has been recognized that several oxygen electrodes such as Sr-doped LaMnO3 (LSM) or La0.6Sr0.4Co0.2Fe0.8O3 - δ (LSCF) suffer from a serious Cr-poisoning.1–3 We have recently succeeded in improving the reversible performances of the single-layer LSCF-Ce0.8Sm0.2O1.9 (SDC) composite O2 electrode with SDC interlayer at 800 and 900 °C,4–6 compared with those of an identical-type electrode in our previous work.7 Though the degradation of the LSM or LSCF electrodes by Cr-poisoning has been studied under either SOFC or SOEC operation mode, separately, to the best of our knowledge, the Cr-poisoning have not been investigated on SOCs under simultaneously reversible operation of SOFC/SOEC modes. Here, we examined for the first time the effect of Cr-poisoning on the performances of LSCF-SDC oxygen electrodes under simultaneously cathodic and anodic polarization conditions in the presence of Fe-Cr alloy. A symmetrical cell [LSCF-SDC ǀSDC interlayerǀ ScSZ electrolyte ǀSDC interlayerǀ LSCF-SDC] was prepared.4,5 Here, we briefly describe the protocol. The SDC interlayer was deposited on both sides of the scandia-stabilized zirconia (ScSZ, (ZrO2)0.89(Sc2O3)0.10(CeO2)0.01) electrolyte by spin coating of Ce(III) 2-ethylhexanoate and Sm(III) 2-ethylhexanoate mixed solution, followed by heat-treatment at 1050 oC for 2 h. The LSCF-SDC paste (60:40 volume ratio) was tape-casted onto the SDC interlayer and heat-treated at 1050 oC for 1 h. The air reference electrode consisted of a Pt wire wound around the ScSZ disk. A commercial Fe-Cr alloy (RA446, 23–27 wt% Cr, Rolled Alloy, Canada) was used as the metallic interconnect without any protective coating. The interconnect plate (12 × 12 × 4 mm) was machined with gas channels on one side. Air was supplied to both electrodes at a flow rate of 100 mL min−1. The as-prepared symmetrical cell was sandwiched with two Fe-Cr interconnect plates, which were also acting as the current collectors. After a constant current density operation at 0.5 A cm−2 and 800 oC for 100 h, the IR-free polarization curves of both electrodes were measured. Hereinafter, the electrodes polarized anodically (O2 evolution) and cathodically (O2reduction) for 100 h will be denoted as electrode A and electrode C, respectively. Figure 1 shows the polarization curves of electrode A and electrode C with and without Fe-Cr interconnect plate at 800 oC. When operated with Pt current collectors (without any Fe-Cr alloy), very high performance of both electrode A and electrode C was observed even after 100 h (negligibly small degradation). In contrast, after operation with Fe-Cr alloy interconnects, the overpotential at both electrodes significantly increased due to Cr-poisoning. While the difference in the anodic overpotential between electrode A and C was relatively small in the O2 evolution reaction, electrode A showed much larger overpotential than that of electrode C in the O2 reduction, specifically at high current densities. This could suggest that Cr-containing oxides deposited in the pores2 might block the O2diffusion path. Analyses of the electrode morphology are under progress. This work was supported by the funds for “ALCA” from Japan Science and Technology Agency. References 1. C. C. Wang, T. Becker, K. Chen, L. Zhao, B. Wei, and S. P. Jiang, Electrochim. Acta, 139, 173 (2014). 2. B. Wei, K. Chen, L. Zhao, Z. Lu, and S. P. Jiang, Phys. Chem. Chem. Phys., 17, 1601 (2015). 3. T. Horita, D. Cho, F. Wang, T. Shimonosono, H. Kishimoto, K. Yamaji, M. E. Brito, and H. Yokokawa, Solid State Ionics, 225, 151 (2012). 4. K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, 23rd Annual Meeting of MRS-J, A-P11-009 (Dec. 9-11, 2013, Yokohama, Japan). 5. K. Shimura, H. Nishino K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, Proc. 81st Annual Meeting of the Electrochemical Society of Japan, 1G17 (2014). 6. H. Uchida, P. Puengjinda, K. Miyano, K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and M. Watanabe, ECS Trans., 68(1), 3307 (2015). 7. Y. Tao, H. Nishino, S. Ashidate, H. Kokubo, M. Watanabe, and H. Uchida, Electrochim. Acta, 54, 3309 (2009). Figure 1

Poisoning of cathodes due to deposition of chromium species from the Fe-Cr alloy interconnect is a major degradation mechanism of solid oxide fuel cell stacks. Our previous studies have shown that the infiltration of gadolinium doped ceria or BaO nanoparticles leads to substantially enhanced chromium resistive ability of La0.6Sr042Co0.2Fe0.8O3 (LSCF) cathodes (Electrochemistry Communications, 37, 84 (2013) and Physical Chemistry Chemical Physics, 17, 4870 (2015)). In this presentation we report BaCeO3 infiltrated LSCF electrodes by co-infiltrating BaO and CeO2 into the LSCF structure and investigate the electrode activity and stability under accelerated chromium poisoning conditions. The results show that 0.8 mg cm-2 BaCeO3 infiltrated LSCF has extraordinary electrocatalytic activity for the oxygen reduction reaction. For example, electrode polarization resistance is 0.12, 0.062, 0.014 and 0.002 Ω cm2 at 650, 700, 750 and 800 oC, respectively. More importantly, the BaCeO3-LSCF electrode is highly tolerant against Cr contamination. For the operation in the presence of bare Fe-Cr alloy without any protective layer, RE is as low as 0.07 Ω cm2 after the polarization at 200 mA cm-2 and 800 oC for 40 h, much smaller than 0.74 Ω cm2 of pristine LSCF cathode after the test under identical conditions. The results imply that the BaCeO3infiltration is an effective means to enhance the electrode activity and stability of LSCF electrodes for operation in the presence of Fe-Cr interconnect.

In high temperature solid oxide fuel cells (SOFCs), electrode/electrolyte interfaces play an ultimate role in the electrocatalytic activity and durability of the cells. In this study, thermally and electrochemically induced electrode/electrolyte interfaces were investigated on pre-sintered and in situ assembled La0.8Sr0.2MnO3 (LSM) electrode on Y2O3-ZrO2 (YSZ) electrolyte, using focus ion beam and high resolution scanning transmission electron microscopy (FIB-STEM). The results indicate that thermally induced interface is characterized by convex contact rings with depth of 100-400 nm and diameter in agreement with the particle size of pre-sintered LSM electrodes, while the cathodic polarization induced interfaces on in situ assembled electrodes are characterized by particle-shaped contact marks (20-50 nm in diameter). The results show that the electrochemical activity of the cathodic polarization induced electrode/electrolyte interface is comparable to the thermally induced one for the O2 reduction reaction under SOFC operation conditions. The FIB-STEM analysis clearly shows that along the rim of the contact rings of pre-sintered LSM electrode, there is formation of a thin layer of La and Sr on the YSZ electrolyte surface, while Mn diffuses into YSZ and the distribution of Mn inside YSZ electrolyte follows closely the profile of the contact rings. The preliminary results provide direct evidences that Mn cation inter-diffusion plays a critical role in the formation of LSM/YSZ interface of SOFCs.

The degradation of solid oxide electrolysis cells (SOECs) is an issue of both scientific and technical importance. In this study, chromium deposition and poisoning at La0.8Sr0.2MnO3+ d (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) oxygen electrodes are studied under SOEC operation conditions. Significant performance degradation was observed for the reaction in the presence of Fe-Cr alloy metallic interconnect, indicating that presence of gaseous Cr species significnatly poisons and degrades the electrocatalytic activity of LSM and LSCF oxygen electrodes. In the case of LSM electrodes, XRD, XPS and SIMS analysis clearly identified the deposition of SrCrO4, CrO2.5 and Cr2O3 phases on the YSZ electrolyte surface and LSM electrode inner surface for the reaction under anodic polarization conditions. In the case of LSCF, Cr deposition occurs in the electrode bulk and on the electrode surface, forming SrCrO4. The results clearly indicate that the Cr deposition is closely related to the increased segregation of SrO species under anodic polarization conditions. The mechanism of the Cr deposition at LSM and LSCF electrodes under SOEC operation conditions is discussed.

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A configuration for the coplanar, single-chamber solid oxide fuel cell has been proposed and operated successfully in a methane-oxygen mixture (CH 4 :0 2 = 2:1) with a total flow of 300 mL min -1 . It was fabricated by attaching the Ni/yttria-stabilized zirconia (YSZ) anode and the Sm 0.2 Ce 0.8 O 1.9 -impregnated La 0.7 Sr 0.3 MnO 3 cathode in two parallel grooves of the YSZ substrate. With the electrolyte wall fabricated between the anode and the cathode, the configuration obviously extends the conductive channel of oxygen ion transport and forms a gas separator between the electrodes, leading to a remarkable reduction in ohmic resistance, an elevation of open-circuit voltage, and, ultimately, an improved performance.

A nanostructured cathode is fabricated by incorporating a mixed ionic and electronic conducting (MIEC) perovskite, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF), via ion impregnation into the most common, highly electronic conducting, and structurally stable La 0.8 Sr 0.2 MnO 3-δ (LSM) porous cathode skeleton. The introduction of nanosized MIEC BSCF particles significantly improves the electrocatalytic activity of the LSM for the oxygen reduction reaction of solid oxide fuel cells at an intermediate temperature range of 600-800°C. The electrode polarization resistance of a 1.8 mg cm -2 BSCF-impregnated LSM cathode is 0.18 Ω cm 2 at 800°C, which is ~12 times lower than that of pure LSM. A single cell with an yttria-stabilized zirconia (YSZ) electrolyte film and the nanostructured BSCF/LSM cathode exhibits maximum power densities of 1.21 and 0.32 W cm -2 at 800 and 650°C, respectively. The atomic force microscopy (AFM) studies of the electrode/electrolyte interface before and after polarization indicate that the impregnation of BSCF extends the three-phase boundary area for the oxygen reduction reaction from the electrode/electrolyte interface to the electrode bulk. The formation of a second phase was also observed by AFM for the BSCF-impregnated LSM after being heat-treated at 800°C though its phase could not be identified due to the extremely small amount of the second phase particles on the YSZ electrolyte surface. The initial structure and polarization performance stability of the nanostructured BSCF-impregnated LSM composite cathodes are also investigated.

Gd 0.2 Ce 0.8 O 1.9 (GDC)-impregnated La 0.8 Sr 0.2 MnO 3 (LSM) electrodes are developed as the anodes for high temperature solid oxide electrolysis cells (SOECs). The effect of anodic polarization current passage on the electrode behavior and microstructure of the LSM- and GDC-impregnated LSM anodes is investigated under low and high currents at 800°C. The results show that the electrocatalytic activity of the freshly prepared LSM is enhanced by the anodic polarization due to the reduction of LSM agglomerates and shrinkage of LSM particles under oxidation conditions at low polarization currents. However, high polarization current leads to the delamination at the interface, resulting in a significant increase in electrode polarization and ohmic resistances for the oxygen oxidation reaction. However, the impregnation of GDC nanoparticles not only enhances significantly the electrocatalytic activity for the oxygen oxidation reaction but also effectively inhibits the electrode delamination at the LSM anode/Y 2 O 3 -ZrO 2 electrolyte interface. The results demonstrate the promising potential of the GDC-impregnated LSM as effective anodes of high temperature SOECs.

Two-cell solid oxide fuel Cell (SOFC) stacks with an anode-facing-cathode configuration were operated in single chamber conditions, i.e., oxygen, methane, and nitrogen mixture. The effect of the distance between two cells on the cell performance was investigated. A single cell consisted of a porous NiO/8 mol % Y(2)O(3)-stabilized ZrO(2) (YSZ) anode support, a YSZ electrolyte membrane, and a Ce(0.8)Sm(0.2)O(1.9)-impregnated La(0.7)Sr(0.3)MnO(3) cathode. The experimental result demonstrated that the effect of the distance on the cathode was quite distinct when the distance (D) was equal to 2 mm. The distance effect could be negligible when D was larger than 4 mm. The effects were also varied with the ratio of methane and oxygen (M). An acceptable value of the distance was critical for the operation and performance of the stack. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3196245] All rights reserved.

Fe-doped (La,Sr)CrO 3―δ (LSCrFe) oxide was modified as the anode of solid oxide fuel cells. Through vacuum-assisted impregnation processes, nanosized Sm-doped CeO 2 (SDC) and Ni particles were introduced into an anode backbone. With Ni and SDC coimpregnated LSCrFe anodes, the maximum power densities at 900°C reached 765 and 271 mW cm ―2 with H 2 and CH 4 as fuels, respectively, which were much higher than that with a nonmodified LSCrFe anode. Our results indicated that nanosized Ni particles played a primary role in performance enhancement. No carbon deposition was detected for all tested LSCrFe-based anodes.

A micro solid oxide fuel cell (SOFC) stack with two series-wound single fuel cells was fabricated and operated successfully under single-chamber conditions. In this stack, the single cells were based on Ni/yttria-stabilized zirconia (YSZ) anode-supported YSZ membrane and were arranged with an anode-facing-cathode configuration in diluted methane and oxygen mixture gas between 600 and 750 degrees C. The performances of the stack were affected by the flow rate, gas composition, and furnace temperature. The effects of the narrow path between two cells on the electrodes and cells were discussed in detail, according to the open-circuit voltages (OCVs) and impedance spectra of each cell. At 700 degrees C, the maximum OCV of the whole stack was larger than 2.0 V at CH4/O-2=1.75 and 2, while the maximum power output of stack was about 371 mW at CH4/O-2=1 with a mass specific power of 552 mW/g. The performance indicates that such microstacks have potential for portable applications. (c) 2007 The Electrochemical Society.