Senin, 13 Juni 2011

Solid Oxide Fuel Cell

1.
Performance of (La,Sr)MnO3 cathode based solid oxide fuel cells: Effect of bismuth oxide sintering aid in silver paste cathode current collector Original Research Article
Journal of Power Sources, Volume 196, Issue 3, 1 February 2011, Pages 928-934
Yunhui Gong, Weijie Ji, Lei Zhang, Bin Xie, Haiqian Wang
Abstract
Effects of a bismuth oxide (Bi2O3) sintering aid in the silver paste cathode current collectors on the electrochemical performance of solid oxide fuel cells with (La,Sr)MnO3 cathode is investigated. Anode-supported single cells are prepared and applied with pure and Bi2O3-added silver pastes for cathode current collecting. Cell performances are evaluated using a current–voltage test and electrochemical impedance spectroscopy. The results indicate that the Bi2O3-added silver paste cathode current collector artificially increases the power density and lowers the polarization resistance of single cell, which may be attributed to the observation of the improved cathode current collector surface morphology and enhanced contact at the cathode-current collector interface, as well as the migration of the Bi2O3 and silver into the cathode from the Bi2O3 contained silver paste cathode current collector.
Keywords: Solid oxide fuel cell; Bismuth oxide; Silver paste current collector; Electrochemical performance

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PDII-LIPI SERPONG

Telp. 021-7560537
E-mail: pdiiserpong@yahoo.com

2.
Synthesis and characterization of Bi31Cr5O61.5, a new bismuth chromium oxide, potential mixed-ionic–electronic conductor for solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 195, Issue 21, 1 November 2010, Pages 7207-7212
Marie Colmont, Michel Drache, Pascal Roussel

3.
Electrochemical characteristics of solid oxide fuel cell cathodes prepared by infiltrating (La,Sr)MnO3 nanoparticles into yttria-stabilized bismuth oxide backbones Original Research Article
International Journal of Hydrogen Energy, Volume 35, Issue 15, August 2010, Pages 8322-8330
Zhiyi Jiang, Zhiwei Lei, Bo Ding, Changrong Xia, Fei Zhao, Fanglin Chen
Abstract
The electrochemical characteristics of the solid oxide fuel cell (SOFC) cathodes prepared by infiltration of (La0.85Sr0.15)0.9MnO3−δ (LSM) nanoparticles into porous Y0.5Bi1.5O3 (YSB) backbones are investigated in terms of overpotential, interfacial polarization resistance, and single cell performance obtained with three-electrode cell, symmetrical cell, and single cell, respectively. X-ray diffraction confirms the formation of perovskite LSM by heating the infiltrated nitrates at 800 °C. The electrical conductivity of the electrode measured using Van der Pauw method is 1.67 S cm−1, which is acceptable at the typical SOFC operating temperatures. The single cell with the LSM infiltrated YSB cathode generates maximum power densities of 0.23, 0.45, 0.78, and 1.13 W cm−2 at 600, 650, 700, and 750 °C, respectively. The oxygen reduction mechanism on the cathode is studied by analyzing the impedance spectra obtained under various temperatures and oxygen partial pressures. The impedance spectra under various cathodic current densities are also measured to study the effect of cathodic polarization on the performance of the cathode.
Keywords: Infiltration; Impedance spectroscopy; Bismuth oxide; Oxygen reduction mechanism; Overpotential; LSM

4.
Thin film ceria–bismuth bilayer electrolytes for intermediate temperature solid oxide fuel cells with La0.85Sr0.15MnO3−δ–Y0.25Bi0.75O1.5 cathodes Original Research Article
Materials Research Bulletin, Volume 45, Issue 5, May 2010, Pages 603-608
Lei Zhang, Changrong Xia, Fei Zhao, Fanglin Chen
Abstract
Thin film electrolytes of bilayer bismuth oxide/ceria are developed for intermediate temperature solid oxide fuel cells. Y0.25Bi0.75O1.5 is deposited via Direct Current magnetron sputtering technique on an Sm0.2Ce0.8O1.90 electrolyte film which is prepared by a dry-pressing process on an NiO–Sm0.2Ce0.8O1.90 substrate. La0.85Sr0.15MnO3−δ–Y0.25Bi0.75O1.5 composite is applied onto the Y0.25Bi0.75O1.5 film as the cathode to form a single cell. Cells with 6-μm-thick Y0.25Bi0.75O1.5 and 26-μm-thick Sm0.2Ce0.8O1.90 bilayer electrolytes exhibit improved open circuit voltages and power density compared with those obtained with only Sm0.2Ce0.8O1.90 electrolytes. The open circuit voltages are comparable and power densities are higher than those previously reported for solid oxide fuel cells with thick bilayer electrolytes using noble metals such as Pt as the electrodes. Impedance spectra show that the change of electrolyte resistance is negligible while the cathodic interfacial polarization resistance decreased significantly when the Y0.25Bi0.75O1.5 layer is added to form the Sm0.2Ce0.8O1.90/Y0.25Bi0.75O1.5 bilayer electrolytes.
Keywords: A. Ceramic; A. Thin film; B. Sputtering; C. Electrochemical measurements; D. Electrochemical properties

5.
Bismuth oxide-coated (La,Sr)MnO3 cathodes for intermediate temperature solid oxide fuel cells with yttria-stabilized zirconia electrolytes Original Research Article
Electrochimica Acta, Volume 54, Issue 11, 15 April 2009, Pages 3059-3065
Zhiyi Jiang, Lei Zhang, Lili Cai, Changrong Xia
Abstract
Taking Y2O3 stabilized Bi2O3 (YSB) as an example, bismuth oxide-added (La,Sr)MnO3 (LSM) is evaluated as a cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs) with 8 mol% Y2O3 stabilized ZrO2 (YSZ) electrolytes. YSB was added to LSM cathodes using an impregnation method, dramatically improving the electrode performance. The interfacial polarization resistance Rp, at 700 °C for the electrode coated with 50 wt.% of YSB is 0.14 Ω cm2, which is only 0.2% of the value for a pure LSM electrode. The high oxygen ionic conductivity and the catalytic activity of YSB, as well as the favorable electrode microstructure are likely reasons for the dramatic reduction of Rp. The YSB-added LSM cathodes also exhibited lower overpotential and higher exchange current density than the pure LSM cathode. Moreover, these electrodes show much lower Rp than that of parallel-fabricated LSM electrodes with samaria-doped-CeO2 as well as other LSM-based electrodes reported in the literature, demonstrating the superiority of the of YSB as the ionic conduction component in composite LSM electrodes. The superior performance of the single cell further demonstrates that the bismuth oxide-added LSM cathode is an excellent candidate for IT-SOFCs.
Keywords: Bismuth oxide; Intermediated temperature SOFC; (La,Sr)MnO3 cathode; Solid oxide fuel cells; Yttria-stabilized zirconia

6.
Nanoscale bismuth oxide impregnated (La,Sr)MnO3 cathodes for intermediate-temperature solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 185, Issue 1, 15 October 2008, Pages 40-48
Zhiyi Jiang, Lei Zhang, Kai Feng, Changrong Xia
Abstract
Bismuth oxide based oxygen ion conductors are incorporated into (La,Sr)MnO3 (LSM), the classical cathode material for solid oxide fuel cells (SOFC), to improve the cathode performance. Yttria-stabilized bismuth oxide (YSB) is taken as an example and is impregnated into a preformed porous LSM frame, forming a highly active cathode for intermediate-temperature SOFCs (IT-SOFCs) with doped ceria electrolytes. X-ray diffraction indicates that YSB is chemically compatible with LSM at intermediate temperatures below 800 °C. The impregnated YSB particles are nanosized and are deposited on the surface of the framework. Significant performance improvement is achieved by introducing nanosized YSB into the LSM electrodes. At 600 °C, the interfacial polarization resistance under open-circuit conditions for electrodes impregnated with 50% YSB is only 1.3% of the original value for a pure LSM electrode. The resistance is further reduced dramatically when current is passed through. In addition, the YSB impregnated LSM electrodes has the highest electrochemical performance among those based on LSM. Single cell with 25% of YSB impregnated LSM cathode generates maximum power density of 300 mW cm−2 at 600 °C, indicating the promise of using LSM-based electrodes for IT-SOFC.
Keywords: Bismuth oxide; Solid oxide fuel cells; Impregnation; Impedance spectroscopy; Composite cathode

7.
Bismuth oxide doped scandia-stabilized zirconia electrolyte for the intermediate temperature solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 160, Issue 2, 6 October 2006, Pages 892-896
S. Sarat, N. Sammes, A. Smirnova
Abstract
Electrical and structural properties of bismuth oxide doped scandia-stabilized zirconia (ScSZ) electrolyte for solid oxide fuel cells (SOFCs) have been evaluated by means of XRD, TGA, DTA, and impedance spectroscopy. The amount of Bi2O3 in the ScSZ was varied in the range of 0.25–2.0 mol%. The original ScSZ samples indicated a rhombohedral crystalline structure that in general has lower conductivity than the cubic phase. However, the addition of Bi2O3 to ScSZ electrolyte was found to stabilize the cubic crystalline phase as detected by XRD. Impedance spectroscopy measurements in the temperature range between 350 and 900 °C indicated a sharp increase in conductivity for the system containing 2 mol% of Bi2O3 that is attributed to the presence of the cubic phase. In addition, impedance spectroscopy measurements revealed significant decrease of both the grain bulk and grain boundary resistances with respect to the temperature change from 600 to 900 °C and concentration of Bi2O3 from 0.5 to 2 mol%. The electrical conductivity at 600 °C obtained for 2 mol% Bi2O3 doped ScSZ was 0.18 S cm−1.
Keywords: Electrolyte; ScSZ; Doping; Bismuth oxide; SOFC

8.
Basic properties of a liquid tin anode solid oxide fuel cell Original Research Article
Journal of Power Sources, Volume 196, Issue 10, 15 May 2011, Pages 4564-4572
Harry Abernathy, Randall Gemmen, Kirk Gerdes, Mark Koslowske, Thomas Tao
Abstract
An unconventional high temperature fuel cell system, the liquid tin anode solid oxide fuel cell (LTA-SOFC), is discussed. A thermodynamic analysis of a solid oxide fuel cell with a liquid metal anode is developed. Pertinent thermochemical and thermophysical properties of liquid tin in particular are detailed. An experimental setup for analysis of LTA-SOFC anode kinetics is described, and data for a planar cell under hydrogen indicated an effective oxygen diffusion coefficient of 5.3 × 10−5 cm2 s−1 at 800 °C and 8.9 × 10−5 cm2 s−1 at 900 °C. This value is similar to previously reported literature values for liquid tin. The oxygen conductivity through the tin, calculated from measured diffusion coefficients and theoretical oxygen solubility limits, is found to be on the same order of that of yttria-stabilized zirconia (YSZ), a traditional SOFC electrolyte material. As such, the ohmic loss due to oxygen transport through the tin layer must be considered in practical system cell design since the tin layer will usually be at least as thick as the electrolyte.

9.
Analytical investigations of varying cross section microstructures on charge transfer in solid oxide fuel cell electrodes Original Research Article
Journal of Power Sources, Volume 196, Issue 10, 15 May 2011, Pages 4695-4704
George J. Nelson, Aldo A. Peracchio, Wilson K.S. Chiu
Abstract
An extended surface modeling concept (electrochemical fin) is applied to charge transport within the SOFC electrode microstructure using an analytical modeling approach analogous to thermal fin analysis. This model is distinct from similar approaches applied to SOFC electrode microstructure in its application of a governing equation that allows for variable cross-section geometry. The model presented is capable of replicating experimentally observed electrode behavior inclusive of sensitivity to microstructural geometry, which stands in contrast to existing models that apply governing equations analogous to a constant cross-section thermal fin equation. Insights learned from this study include: the establishment of a suite of dimensionless parameters and performance metrics that can be applied to assess electrode microstructure, the definition of microstructure-related transport regimes relevant to electrode design, and correlations that allow performance predictions for electrodes that provide cell structural support. Of particular note, the variable cross-section modeling approach motivates the definition of a sintering quality parameter that quantifies the degree of constriction within the conducting network of the electrode, a phenomenon that exerts influence over electrode polarization. One-dimensional models are presented for electrochemical fins of several cross-sectional geometries with the ultimate goal of developing a general tool that enables the prompt performance evaluation of electrode microstructures. Such a tool would facilitate SOFC microstructural design by focusing more detailed modeling efforts on the most promising microstructures.
Keywords: Solid oxide fuel cell; Heterogeneous functional materials; Transport phenomena; Electrode microstructure

10.
Development of solid oxide fuel cell materials for intermediate-to-low temperature operation Original Research Article
International Journal of Hydrogen Energy, In Press, Corrected Proof, Available online 14 May 2011
Jianbing Huang, Fucheng Xie, Cheng Wang, Zongqiang Mao
Abstract
The commercialization of solid oxide fuel cell (SOFC) needs the development of functional materials for intermediate-to-low temperature (400–700 °C, ILT) operation. Recently, we have successfully developed new electrolyte materials for ILT-SOFCs, including Ce0.8Sm0.2O1.9 (SDC), BaCe0.8Sm0.2O2.9 (BCSO) and SDC-carbonate composites. Compared with the state-of-the-art yttria-stabilized zirconia (YSZ), these materials exhibit much higher ionic conductivity at ILT range. Especially, SDC-carbonate composites show an ionic conductivity of 10−2 to 1 Scm−1 between 400 and 600 °C in fuel cell environment. Some new cathode materials were investigated for above electrolyte materials and showed promising performance. Alternative anode materials were developed to directly utilize alcohol fuels. A dry-pressing and co-firing process was employed to fabricate thin SDC and BCSO electrolyte membranes as well as thick SDC-carbonate composite electrolyte with acceptable density on anode substrate. Many efforts have also been made on fabrication of larger-size planar cells and exploitation of reliable sealing materials.

11.
Ni-Sm2O3 cermet anodes for intermediate-temperature solid oxide fuel cells with stabilized zirconia electrolytes Original Research Article
International Journal of Hydrogen Energy, Volume 36, Issue 9, May 2011, Pages 5589-5594
Beibei He, Ling Zhao, Shuxiang Song, Zhiyi Jiang, Changrong Xia
Abstract
Ni-LnOx cermets (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd), in which LnOx is not an oxygen ion conductor, have shown high performance as the anodes for low-temperature solid oxide fuel cells (SOFCs) with doped ceria electrolytes. In this work, Ni-Sm2O3 cermets are primarily investigated as the anodes for intermediate-temperature SOFCs with scandia stabilized zirconia (ScSZ) electrolytes. The electrochemical performances of the Ni-Sm2O3 anodes are characterized using single cells with ScSZ electrolytes and LSM-YSB composite cathodes. The Ni-Sm2O3 anodes exhibit relatively lower performance, compared with that reported Ni-SDC (samaria doped ceria) and Ni-YSZ (yttria stabilized zirconia) anodes, the state-of-the-art electrodes for SOFCs based on zirconia electrolytes. The relatively low performance is possibly due to the solid-state reaction between Sm2O3 and ScSZ in fuel cell fabrication processes. By depositing a thin interlayer between the Ni-Sm2O3 anode and the ScSZ electrolyte, the performance is substantially improved. Single cells with a Ni-SDC interlayer show stable open circuit voltage, generate peak power density of 410 mW cm−2 at 700 °C, and the interfacial polarization is about 0.7 Ω cm2.

12.
Nanosized Ce0.8Sm0.2O1.9 infiltrated GdBaCo2O5+δ cathodes for intermediate-temperature solid oxide fuel cells Original Research Article
International Journal of Hydrogen Energy, Volume 36, Issue 10, May 2011, Pages 6151-6159
Bo Wei, Zhe Lü, Tianshi Wei, Dechang Jia, Xiqiang Huang, Yaohui Zhang, Jipeng Miao, Wenhui Su
Abstract
In this paper, Ce0.8Sm0.2O1.9 (SDC) nanoparticles modified GdBaCo2O5+δ (GBCO) cathodes were fabricated by an infiltration technique and evaluated for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Good chemical compatibility between GBCO and infiltrated SDC was confirmed by X-ray diffraction (XRD) characterization. SDC nanoparticles ( 40 nm) formed continuous ionic-conducting phase on porous GBCO backbone, which contributed to significantly improved electro-catalytic property. At 600 °C, the composite cathode with 3.3 mg cm−2 SDC loading exhibited encouragingly low Rp value of 0.1 Ω cm2, which was much lower than 0.43 Ω cm2 of pure-GBCO cathode. As revealed by PO2 dependence of impedance spectra, the oxygen reduction reaction was mainly limited by charge-transfer processes. Furthermore, a stable operation of 80 h was obtained at 600 °C. Our study implies that infiltrated GBCO cathode is very attractive for application in IT-SOFC cathode.
Keywords: Solid oxide fuel cell; GdBaCo2O5+δ cathode; Infiltration; Electrochemical impedance spectra

13.
Solid oxide fuel cells with YSZ-BNO Bi-layer electrolyte film deposited by magnetron sputtering Original Research Article
Ceramics International, In Press, Corrected Proof, Available online 8 April 2011
Sea-Fue Wang, Yung-Fu Hsu, Yu-Chia Huang, Wen-Cheng Wei
Abstract
Bi-layer electrolyte films of Zr0.84Y0.16O1.92 (YSZ)- 0.79Bi2O3-0.21Nb2O5 (BNO) were deposited by RF magnetron sputtering on NiO-SDC anode substrates. The stoichiometry of the BNO electrolyte film was found strongly dependent on the ratio of Ar and O2 during sputtering, and the BNO film deposited at a mixture of 31 sccm Ar and 7 sccm O2 appeared to be the closest to the target composition. When deposited at 300 °C and subsequently annealed at 700 °C, the BNO electrolyte emerged to be crack free and dense with some scattering closed pores. The XRD patterns of the film are indexed to the cubic Fm m structure of Bi3NbO7. The as-deposited film was well-crystalline and consisted of fine grains and random orientation microstructures. For electrolyte thicknesses of approximately 4.0 μm YSZ and 1.5 μm BNO layers, the open circuit voltage (OCV) and the maximum power density of the single cell with Ag cathode read respectively 0.94 V and 10 mW/cm2 at 600 °C. These OCV values are lower than the expected theoretical value due to the high partial electronic conductivity.
Keywords: Solid oxide fuel cell; Bi-layer electrolyte; Sputtering; Electrolyte

14.
Structural, thermal and crystallization kinetics of ZnO–BaO–SiO2–B2O3–Mn2O3 based glass sealants for solid oxide fuel cells Original Research Article
Ceramics International, In Press, Corrected Proof, Available online 8 April 2011
Anu Arora, Vishal Kumar, K. Singh, O.P. Pandey
Abstract
Glass compositions in the system 40SiO2–30BaO–20ZnO–(x)Mn2O3–(10 − x)B2O3 glasses have been synthesized and the thermal, structural and crystallization kinetic properties characterized. The lower concentration of Mn2O3 in place of B2O3 acts as a network former and suppressed the tendency of phase separation in glasses. On the other hand, concentration of Mn2O3 > 7.5 mol% induce phase separation in the glass matrix. The highest activation energy for crystallization is observed in the composition without B2O3 (INM4) (355 kJ/mol). The values of thermal expansion coefficient (TEC) and viscosity of this glass is 8 × 10−6 K−1 and 104.2dPa s (850 °C), respectively. After long heat treatment (800 °C for 100 h), thermodynamically stable hexacelsian and monoclinic phases are formed. These phases are not detrimental to SOFC application.
Keywords: Scanning electron microscopy; X-ray diffraction; Fuel cells; Glass

15.
Synthesis and sintering of Gd-doped CeO2 electrolytes with and without 1 at.% CuO dopping for solid oxide fuel cell applications Original Research Article
International Journal of Hydrogen Energy, Volume 36, Issue 8, April 2011, Pages 5054-5066
Yingchao Dong, Stuart Hampshire, Jian-er Zhou, Guangyao Meng
Abstract
Nano-sized Ce0.8Gd0.2O2−δ and Ce0.79Gd0.2Cu0.01O2−δ electrolyte powders were synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by powder characteristics, sintering behaviors and electrical properties. The results demonstrate that the as-synthesized Ce0.8Gd0.2O2−δ and Ce0.79Gd0.2Cu0.01O2−δ possessed similar powder characteristics, including cubic fluorite crystalline structure, porous foamy morphology and agglomerated secondary particles composed of gas cavities and primary nano crystals. Nevertheless, after ball-milling these two powders exhibited quite different sintering abilities. A significant reduction of about 400 °C in densification temperature of Ce0.79Gd0.2Cu0.01O2−δ was obtained when compared with Ce0.8Gd0.2O2−δ. The Ce0.79Gd0.2Cu0.01O2−δ pellets sintered at 1000 °C and the Ce0.8Gd0.2O2−δ sintered at 1400 °C exhibited relative densities of 96.33% and 95.7%, respectively. The sintering of Ce0.79Gd0.2Cu0.01O2−δ was dominated by the liquid phase process, followed by the evaporation-condensation process, Moreover, Ce0.79Gd0.2Cu0.01O2−δ shows much higher conductivity of 0.026 S cm−1 than Ce0.8Gd0.2O2−δ (0.0065 S cm−1) at a testing temperature of 600 °C.

16.
Evaluation and optimization of Bi1−xSrxFeO3−δ perovskites as cathodes of solid oxide fuel cells Original Research Article
International Journal of Hydrogen Energy, Volume 36, Issue 4, February 2011, Pages 3179-3186
Yingjie Niu, Jaka Sunarso, Wei Zhou, Fengli Liang, Lei Ge, Zhonghua Zhu, Zongping Shao
Abstract
Lattice expansion behaviour, oxygen nonstoichiometry, mean iron oxidation state, electrical conductivity and interfacial polarization resistance of Bi1−xSrxFeO3−δ were reported as a function of Sr-doping content for x = 0.3, 0.5 and 0.8. Among the series, Bi0.5Sr0.5FeO3−δ (BSF5) demonstrates the optimum performance in terms of the lowest interfacial polarization resistance and the largest oxygen nonstoichiometry. It is demonstrated that the best microstructure and the lowest interfacial resistance can be obtained by firing BSF5 onto dense Sm0.2Ce0.8O1.9 (SDC) electrolyte at 1000 °C. BSF5 exhibits good chemical compatibility with SDC; however, firing temperature above 1000 °C results in the formation of bismuth-deficient perovskite with inferior activity for oxygen reduction reaction. We also show that single-phase BSF5 cathode provides better electrode performance than its composite with SDC. This is due to the increased charge-transfer resistance upon adding SDC which have negligible electronic conductivity.
Keywords: Solid oxide fuel cells; Perovskite; Bismuth; Cathode

17.
Bi0.5Sr0.5MnO3 as cathode material for intermediate-temperature solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 196, Issue 3, 1 February 2011, Pages 999-1005
Beibei Liu, Zhiyi Jiang, Bo Ding, Fanglin Chen, Changrong Xia
Abstract
Bi0.5Sr0.5MnO3 (BSM), a manganite-based perovskite, has been investigated as a new cathode material for intermediate-temperature solid oxide fuel cells (SOFCs). The average thermal-expansion coefficient of BSM is 14 × 10−6 K−1, close to that of the typical electrolyte material. Its electrical conductivity is 82–200 S cm−1 over the temperature range of 600–800 °C, and the oxygen ionic conductivity is about 2.0 × 10−4 S cm−1 at 800 °C. Although the cathodic polarization behavior of BSM is similar to that of lanthanum strontium manganite (LSM), the interfacial polarization resistance of BSM is substantially lower than that of LSM. The cathode polarization resistance of BSM is only 0.4 Ω cm2 at 700 °C and it decreases to 0.17 Ω cm2 when SDC is added to form a BSM–SDC composite cathode. Peak power densities of single cells using a pure BSM cathode and a BSM–SDC composite electrode are 277 and 349 mW cm2 at 600 °C, respectively, which are much higher than those obtained with LSM-based cathode. The high electrochemical performance indicates that BSM can be a promising cathode material for intermediate-temperature SOFCs.
Keywords: Cathode; Perovskite; Manganite; Solid oxide fuel cells

18.
Synthesis and characterization of Ca-substituted YAlO3 by pechini route for solid oxide fuel cells Original Research Article
Solid State Sciences, Volume 13, Issue 1, January 2011, Pages 168-174
Ramya Hariharan, Prakash Gopalan
Abstract
The high operating temperature requirement of solid oxide fuel cells demands electrolyte materials stable at temperatures around 800 °C. The perovskite material YAlO3, with yttrium ion on the A-site and the aluminium ion on the B-site is being investigated as an electrolyte for solid oxide fuel cells. This work investigates the structure and electrical conductivity of undoped and Ca-doped YAlO3 compositions that has been synthesized by the Pechini route. The samples have been investigated by X-ray diffraction studies. The electrical conductivity studies have been performed using a.c impedance spectroscopy in the range 200–800 °C in air. The doped YAlO3 of composition x = 0.1 exhibits a total conductivity of about 2.2 mS/cm at 800 °C. The microstructural evaluation of the samples has been conducted by scanning electron microscopy coupled with energy dispersive spectrum analysis.

19.
A novel design of anode-supported solid oxide fuel cells with Y2O3-doped Bi2O3, LaGaO3 and La-doped CeO2 trilayer electrolyte
Journal of Power Sources, Volume 195, Issue 24, 15 December 2010, Pages 8185-8188
Weimin Guo, Jiang Liu
Abstract
Anode-supported solid oxide fuel cells (SOFCs) with a trilayered yttria-doped bismuth oxide (YDB), strontium- and magnesium-doped lanthanum gallate (LSGM) and lanthanum-doped ceria (LDC) composite electrolyte film are developed. The cell with a YDB (18 μm)/LSGM (19 μm)/LDC (13 μm) composite electrolyte film (designated as cell-A) shows the open-circuit voltages (OCVs) slightly higher than that of a cell with an LSGM (31 μm)/LDC (17 μm) electrolyte film (designated as cell-B) in the operating temperature range of 500–700 °C. The cell-A using Ag-YDB composition as cathode exhibits lower polarization resistance and ohmic resistance than those of a cell-B at 700 °C. The results show that the introduction of YDB to an anode-supported SOFC with a LSGM/LDC composite electrolyte film can effectively block electronic transport through the cell and thus increased the OCVs, and can help the cell to achieve higher power output.
Keywords: Solid oxide fuel cells; Yttria-doped bismuth oxide; Strontium- and magnesium-doped lanthanum gallate; Trilayered composite electrolyte film; Comparison; Improvement

20.
Synthesis of nanostructured BSCF by oxalate co-precipitation – As potential cathode material for solid oxide fuels cells Original Research Article
International Journal of Hydrogen Energy, Volume 35, Issue 17, September 2010, Pages 9448-9454
Muhammet S. Toprak, Mahdi Darab, Guttorm Ernst Syvertsen, Mamoun Muhammed
Abstract
BaxSr1−xCoyFe1−yO3 (BSCF) cathode material for solid oxide fuel cells (SOFC) was synthesized in nanocrystalline form by a novel chemical alloying approach. Thermodynamic modeling has been performed using Medusa software for obtaining the optimum conditions for the fabrication of a precursor with the desired composition. Precursor powder was then calcined and annealed to produce the final mixed oxide BSCF composition. The thermal properties, phase constituents, microstructure and elemental analysis of the samples were characterized by TGA, XRD, SEM and EDS techniques respectively. Spark Plasma Sintering (SPS) has been used at 1080 °C and under 50 MPa pressure to obtain the pellets of BSCF with preserved nanostructure and rather high compaction density for electrical conductivity measurements. The results show that the powders have cubic perovskite-type structure with a high homogeneity. Finer resultant powder, compared to earlier reports, and SPS sintered BSCF with nanosized grains exhibited a significantly higher electrical conductivity up to 900 °C. Specific conductivity values have been measured in air and N2 and the maximum of 63 S cm−1 at 430 °C in air and 25 S cm−1 at 375 °C in N2 correspondingly show twice as much as conventional BSCF implying a high pledge for nano-BSCF as cathode material in intermediate-temperature SOFC. This is due to the lower interfacial resistance of preserved nanograins by the use of SPS sintering. Presented co-precipitation method is easy to handle and has a high promise to synthesize BSCF at large-scale for IT-SOFCs.
Keywords: Solid oxide fuel cell; Nanostructure; BSCF; Co-precipitation; Nanocrystalline perovskites

21.
Effect of A2O3 (A = La, Y, Cr, Al) on thermal and crystallization kinetics of borosilicate glass sealants for solid oxide fuel cells Original Research Article
Ceramics International, Volume 36, Issue 5, July 2010, Pages 1621-1628
Vishal Kumar, O.P. Pandey, K. Singh
Abstract
Influence of various intermediate oxides on thermal, structural and crystallization kinetics of 30BaO–40SiO2–20B2O3–10A2O3 (A = Y, La, Al, Cr) glasses has been studied. The highest glass transition temperature (Tg) with high thermal stability is observed in Y2O3 containing glasses as compared to other glasses. The thermal expansion coefficient (TEC) increases with increasing heat treatment duration in all the glasses. The maximum increase in TEC is observed in Cr2O3 containing glass ceramics. FTIR study showed that transmission bands due to silicate and borate chains become sharper with splitting after heat treatment. A selected glass sample (BaCr) has been tested for interaction and adhesion with Crofer 22 APU interconnect material for its application as a sealant in solid oxide fuel cell.
Keywords: C. Thermal expansion; D. Glass; D. Glass ceramics; E. Fuel cells; Scanning electron microscopy

22.
Stable glass-ceramic sealants for solid oxide fuel cells: Influence of Bi2O3 doping Original Research Article
International Journal of Hydrogen Energy, Volume 35, Issue 13, July 2010, Pages 6911-6923
Ashutosh Goel, Maria J. Pascual, José M.F. Ferreira
Abstract
Diopside (CaMgSi2O6) based glass-ceramics in the system SrO–CaO–MgO–Al2O3–B2O3–La2O3–Bi2O3–SiO2 have been synthesized for sealing applications in solid oxide fuel cells (SOFC). The parent glass composition in the primary crystallization field of diopside has been doped with different amounts of Bi2O3 (1, 3, 5 wt.%). The sintering behavior by hot-stage microscopy (HSM) reveals that all the investigated glass compositions exhibit a two-stage shrinkage behavior. The crystallization kinetics of the glasses has been studied by differential thermal analysis (DTA) while X-ray diffraction adjoined with Rietveld-R.I.R. analysis have been employed to quantify the amount of crystalline and amorphous phases in the glass-ceramics. Diopside and augite crystallized as the primary crystalline phases in all the glass-ceramics. The coefficient of thermal expansion (CTE) of the investigated glass-ceramics varied between (9.06–10.14) × 10−6 K−1 after heat treatment at SOFC operating temperature for a duration varying between 1 h and 200 h. Further, low electrical conductivity, good joining behavior and negligible reactivity with metallic interconnects (Crofer22 APU and Sanergy HT) in air indicate that the investigated glass-ceramics are suitable candidates for further experimentation as sealants in SOFC.
Keywords: Solid oxide fuel cell; Glass-ceramic sealant; Diopside; Sintering; Interconnect; X-ray diffraction

23.
A high performance solid oxide fuel cells operating at intermediate temperature with a modified interface between cathode and electrolyte Original Research Article
Journal of the European Ceramic Society, Volume 30, Issue 8, June 2010, Pages 1803-1808
Baoan Fan, Jiabao Yan, Wenping Shi
Abstract
By adding 1% Bi2O3 (mol%) into LSCF (La0.54Sr0.44Co0.2Fe0.8O3−δ), a layer of dense LSCF film is introduced to the upside of yttria stabilized zirconia (YSZ) electrolyte. The dense film increases the interface contact area and reduces the interface ion transfer resistance between cathode and electrolyte remarkably. As a result, the cell performance is greatly elevated from 492 to 901 mW cm−2 at 650 °C. Besides, on the basis of careful observation of the cathode surface by FE-SEM, the function of Bi2O3 to promote the cathode sintering is speculated. The Bi2O3 and the LSCF come into being a kind of eutectic liquid. The eutectic liquid flows down from the cathode bulk to the interface between the cathode and the electrolyte where it accumulates to form a dense layer. This dense layer illuminates the function of adding Bi2O3 into LSCF cathode.
Keywords: Sintering; Interface; Electrical properties; Solid oxide fuel cells; Bismuth oxide

24.
Hydrothermal preparation and electrochemical properties of Gd3+ and Bi3+, Sm3+, La3+, and Nd3+ codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cell Original Research Article
Journal of Power Sources, Volume 195, Issue 9, 1 May 2010, Pages 2488-2495
Sibel Dikmen, Hasan Aslanbay, Erdal Dikmen, Osman Şahin
Abstract
The structure, the thermal expansion coefficient, electrical conductivities of Ce0.8Gd0.2−xMxO2−δ (for M: Bi, x = 0–0.1, and for M: Sm, La, and Nd, x = 0.02) solid solutions, prepared for the first time hydrothermally, are investigated. The uniformly small particle size (28–59 nm) of the materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C. The maximum conductivity, σ700 °C around 4.46 × 10−2 S cm−1 with Ea = 0.52 eV, is found at x = 0.1 for Bi-co-doping. Among various metal-co-dopings, for x = 0.02, the maximum conductivity, σ700 °C around 2.88 × 10−2 S cm−1 with Ea = 0.67 eV, is found for Sm-co-doping. The electrolytic domain boundary (EDB) of Ce0.8Gd0.1Bi0.1O2−δ is found to be 1.2 × 10−19 atm, which is relatively lower than that of the singly doped samples. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.6 × 10−6 K−1 for the CeO2, 12.1 × 10−6 K−1 for Ce0.8Gd0.2O2−δ, and increase with co-doping to 14.2 × 10−6 K−1 for Ce0.8Gd0.18Bi0.02O2−δ. The maximum power densities for the single cell based on the codoped samples are higher than that of the singly doped sample. These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.
Keywords: SOFC; Hydrothermal preparation; Co-doping

25.
Au@BICUVOX10 composite cathode for novel structure low-temperature solid-oxide fuel cells Original Research Article
Journal of Power Sources, Volume 195, Issue 9, 1 May 2010, Pages 2514-2519
Tao Yang, Fan Li, Dingguo Xia
Abstract
A composite Au@Bi2Cu0.1V0.9O5.35 (BICUVOX10) cathode is prepared and tested as a ceramal electrode for use in low-temperature solid-oxide fuel cells (SOFCs). Au powder is coated onto the surface of BICUVOX10 from an aqueous solution of the chloride with NaBH4 as a reductant. The valence of the surface Au is identified as Au(0) by X-ray photoelectron spectroscopy (XPS). The BICUVOX10 substrate is synthesized from V2O3, CuO, and Bi2O3 and then investigated by field-emission scanning electron microscopy (SEM). The average size of the particles is estimated to be 100 nm after milling with a planetary ball-mill. The core–shell structure of Au@BICUVOX10 is confirmed by transmission electron microscopy (TEM). The two-dimensional coefficient of thermal expansion (CTE) and the conductivities of mixed powders with different proportions of Au is also tested from room temperature to 600 °C. A single fuel cell is fabricated with Au@BICUVOX10 as the cathode, NiO/GDC (Gd0.1Ce0.9O1.95) as the supporting anode, and GDC as the electrolyte. The electrochemical performance is tested and the highest power densities of the fuel cell are determined to be 127, 206, 359, 469, and 474 mW cm−2 at 450, 500, 525, 550, and 575 °C, respectively. Finally, the stability of the single SOFC is tested, whereupon it is found that its output is maintained for at least the first 20 h.
Keywords: Cathode; Au nanoparticles; BICUVOX10; Core–shell structure; Low-temperature SOFC

26.
Nano-structured composite cathodes for intermediate-temperature solid oxide fuel cells via an infiltration/impregnation technique Review Article
Electrochimica Acta, Volume 55, Issue 11, 15 April 2010, Pages 3595-3605
Zhiyi Jiang, Changrong Xia, Fanglin Chen
Abstract
Solid oxide fuel cells (SOFCs) are high temperature energy conversion devices working efficiently and environmental friendly. SOFC requires a functional cathode with high electrocatalytic activity for the electrochemical reduction of oxygen. The electrode is often fabricated at high temperature to achieve good bonding between the electrode and electrolyte. The high temperature not only limits material choice but also results in coarse particles with low electrocatalytic activity. Nano-structured electrodes fabricated at low temperature by an infiltration/impregnation technique have shown many advantages including superior activity and wider range of material choices. The impregnation technique involves depositing nanoparticle catalysts into a pre-sintered electrode backbone. Two basic types of nano-structures are developed since the electrode is usually a composite consists of an electrolyte and an electrocatalyst. One is infiltrating electronically conducting nano-catalyst into a single phase ionic conducting backbone, while the other is infiltrating ionically conducting nanoparticles into a single phase electronically conducting backbone. In addition, nanoparticles of the electrocatalyst, electrolyte and other oxides have also been infiltrated into mixed conducting backbones. These nano-structured cathodes are reviewed here regarding the preparation methods, their electrochemical performance, and stability upon thermal cycling.
Keywords: Infiltration; Impregnation; Solid oxide fuel cell; Cathode

27.
Preparation and characterization of neodymium-doped ceria electrolyte materials for solid oxide fuel cells Original Research Article
Ceramics International, Volume 36, Issue 2, March 2010, Pages 483-490
Yen-Pei Fu, Sih-Hong Chen
Abstract
The microstructure, thermal expansion, microhardness, indentation fracture toughness, and ionic conductivity of neodymium-doped ceria (NDC) prepared by coprecipitation were investigated. The results revealed that the average particle size (DBET) ranged from 20.1 to 25.8 nm, crystallite dimension (DXRD) varied from 17.5 to 20.7 nm, and the specific surface area distribution was from 31.25 to 40.27 m2/g for neodymium-doped ceria stacking powders. Dependence of lattice parameter, a, versus dopant concentration, x, of Nd3+ ion shows that these solid solutions obey Vegard's rule as a(x) = 5.4069 + 0.1642x for Ce1−xNdxO2−(1/2)x for x = 0.05–0.25. For neodymium-doped ceria ceramics sintered at 1500 °C for 5 h, the bulk density was over 95% of the theoretical density. The maximum ionic conductivity, σ800°C = 4.615 × 10−2 S/cm, with the minimum activation energy, Ea = 0.794 eV was found for the Ce0.75Nd0.25O1.875 ceramic. Trivalent, neodymium-doped ceria ceramics revealed high fracture toughness, the fracture toughness distribution was in the range of 6.236 ± 0.021 to 6.846 ± 0.017 MPa m1/2. The high indentation fracture toughness of neodymium-doped ceria was attributed to crack deflection. Moreover, the porosity may influence the mechanical properties such as microhardness and fracture toughness. It was observed that as the porosity reduced, the microhardness and fracture toughness increased.
Keywords: A. Powders: chemical preparation; C. Fracture; C. Ionic conductivity; D. CeO2; E. Fuel cells

28.
La0.84Sr0.16MnO3−δ cathodes impregnated with Bi1.4Er0.6O3 for intermediate-temperature solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 194, Issue 2, 1 December 2009, Pages 625-630
Junliang Li, Shaorong Wang, Zhenrong Wang, Renzhu Liu, Tinglian Wen, Zhaoyin Wen
Abstract
La0.84Sr0.16MnO3−δ–Bi1.4Er0.6O3 (LSM–ESB) composite cathodes are fabricated by impregnating LSM electronic conducting matrix with the ion-conducting ESB for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The performance of LSM–ESB cathodes is investigated at temperatures below 750 °C by AC impedance spectroscopy. The ion-impregnation of ESB significantly enhances the electrocatalytic activity of the LSM electrodes for the oxygen reduction reactions, and the ion-impregnated LSM–ESB composite cathodes show excellent performance. At 750 °C, the value of the cathode polarization resistance (Rp) is only 0.11 Ω cm2 for an ion-impregnated LSM–ESB cathode, which also shows high stability during a period of 200 h. For the performance testing of single cells, the maximum power density is 0.74 W cm−2 at 700 °C for a cell with the LSM–ESB cathode. The results demonstrate the ion-impregnated LSM–ESB is one of the promising cathode materials for intermediate-temperature solid oxide fuel cells.
Keywords: Intermediate-temperature solid oxide fuel cells; Composite cathode; Impedance spectroscopy; Ion-impregnation; Bismuth oxides

29.
Sintering of 4YSZ (ZrO2 + 4 mol% Y2O3) nanoceramics for solid oxide fuel cells (SOFCs), their structure and ionic conductivity Original Research Article
Journal of the European Ceramic Society, Volume 29, Issue 12, September 2009, Pages 2537-2547
Dagfinn Mæland, Crina Suciu, Ivar Wærnhus, Alex C. Hoffmann
Abstract
In this work 4YSZ nanoparticles were produced with a variant of the sol–gel method, the particles were sintered using two different heating schemes, and the properties of the resulting pellets investigated. XRD spectra show the crystal structure of the particles to be mainly cubic, and TEM pictures reveal their size to be around 20 nm. The relative densities of the sintered pellets are found with the Archimedes method to lie between 87 and 97% of the theoretical material density, and the grain size, using thermal etching and SEM imaging, found to lie between 0.2 and 5 m, depending on the sintering temperature and the presence of impurities. The pellets were subjected to electrical impedance spectroscopy making it possible to distinguish the internal crystal and grain boundary impedances due to their different time-constants. With the “brick layer model” the approximate grain boundary thickness was found to lie between 4 and 8 nm, depending on the sintering conditions and on the presence of impurities. The specific resistances of the grain interiors and the grain boundaries, and the activation energies for ion diffusion in both, are presented. The ionic conductivities of the pellets are compared with literature values, and are found to compare favorably with these, at some temperatures even with data for 8YSZ, which is the standard material used for electrolytes due to its higher ionic conductivity, but which is also mechanically weaker than 4YSZ.
Keywords: Grain growth; Grainboundaries; Nanocomposites; Impedance; Solid oxide fuel cells; 4YSZ; Nanoparticles; Sintering temperature; Electrical impedance

30.
Measurement of oxygen chemical potential in Gd2O3-doped ceria-Y2O3-stabilized zirconia bi-layer electrolyte, anode-supported solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 192, Issue 2, 15 July 2009, Pages 267-278
Hyung-Tae Lim, Anil V. Virkar
Abstract
Solid oxide fuel cells (SOFC) were fabricated with gadolinia-doped ceria (GDC)–yttria stabilized zirconia (YSZ), thin bi-layer electrolytes supported on Ni + YSZ anodes. The GDC and YSZ layer thicknesses were 45 μm, and 5 μm, respectively. Two types of cells were made; YSZ layer between anode and GDC (GDC/YSZ) and YSZ layer between cathode and GDC (YSZ/GDC). Two platinum reference electrodes were embedded within the GDC layer. Cells were tested at 650 °C with hydrogen as fuel and air as oxidant. Electric potentials between embedded reference electrodes and anode and between cathode and anode were measured at open circuit, short circuit and under load. The electric potential was nearly constant through GDC in the cathode/YSZ/GDC/anode cells. By contrast, it varied monotonically through GDC in the cathode/GDC/YSZ/anode cells. Estimates of oxygen chemical potential, μO2, variation through GDC were made. μO2 within the GDC layer in the cathode/GDC/YSZ/anode cell decreased as the current was increased. By contrast, μO2 within the GDC layer in the cathode/YSZ/GDC/anode cell increased as the current was increased. The cathode/YSZ/GDC/anode cell exhibited maximum power density of 0.52 W cm−2 at 650 °C while the cathode/GDC/YSZ/anode cell exhibited maximum power density of 0.14 W cm−2 for the same total electrolyte thickness.
Keywords: Ceria; Zirconia; Bi-layer; Solid oxide fuel cells; Oxygen chemical potential

31.
High-performance bilayered electrolyte intermediate temperature solid oxide fuel cells
Electrochemistry Communications, Volume 11, Issue 7, July 2009, Pages 1504-1507
Jin Soo Ahn, Daniele Pergolesi, Matthew A. Camaratta, Heesung Yoon, Byung Wook Lee, Kang Taek Lee, Doh Won Jung, Enrico Traversa, Eric D. Wachsman
Abstract
The ESB/GDC bilayer electrolyte concept has been proved to improve open circuit voltage and reduce the effective area specific resistance of SOFCs utilizing a conventional single-layer GDC electrolyte. However, high performance from such bilayer cells had not yet been demonstrated. The main obstacles toward this end have been fabrication of anode-supported thin-film electrolytes and the reactivity of ESB with conventional cathodes. Recently, an ESB-compatible low area specific resistance cathode was developed: microstructurally optimized Bi2Ru2O7-ESB composites. In addition, we recently developed a novel anode functional layer which can significantly enhance the performance of SOFC utilizing GDC electrolytes. This study combines these recent achievements in SOFC studies and shows that exceptionally high performance of SOFC is possible using ESB/GDC bilayer electrolytes and Bi2Ru2O7-ESB composite cathodes. The result confirms that the bilayer electrolyte and the Bi2Ru2O7-ESB cathode can increase the open circuit potential and reduce the total area specific resistance. The maximum power density of the bilayered SOFC was improved to 1.95 W cm−2 with 0.079 Ω cm2 total cell area specific resistance at 650 °C. This is the highest power yet achieved in the IT range and we believe redefines the expectation level for maximum power under IT-SOFC operating conditions.
Keywords: SOFC; IT-SOFC; Bilayered electrolyte; Bilayer electrolyte; ESB; GDC

32.
LaGaO3-based cermet for solid oxide fuel cell cathodes
Original Research Article
Journal of the European Ceramic Society, Volume 29, Issue 8, May 2009, Pages 1469-1476
Pradyot Datta, Peter Majewski, Fritz Aldinger
Abstract
A series of La0.9Sr0.1Ga0.85Mg0.15O3−δ–Ag cermets with different Ag2O contents were prepared by conventional sintering, assessing their suitability as cathode material for solid oxide fuel cell (SOFC) in combination with Sr- and Mg-doped LaGaO3 electrolytes. Ag2O is found to get dissociated at around 320 °C. The chemical compatibility between La0.9Sr0.1Ga0.85Mg0.15O3−δ–Ag (LSGM) and Ag was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. No reaction or solid solubility between LSGM and Ag was found. Thermal expansion coefficients of the cermets were measured as a function of Ag content and were found to increase with increasing metallic content. Oxygen adsorption at the surface of the cermets could be detected.
Keywords: Oxide materials; Composite cathode; Thermal expansion; Photoelectron spectroscopies; X-ray diffraction

33.
FUEL CELLS - SOLID OXIDE FUEL CELLS | Overview
Encyclopedia of Electrochemical Power Sources, 2009, Pages 1-16
X.-D. Zhou, S.C. Singhal
Abstract
A solid oxide fuel cell (SOFC) is an electrochemical device to directly convert the chemical energy of a fuel into electricity at temperatures from 500 to 1000 °C. The high operational temperature offers certain advantages over lower temperature fuel cells, notably fuel flexibility, and can use carbon monoxide as a fuel and not become poisoned by it. Solid oxide fuel cells operate at high overall efficiency because of the use of high-grade exhaust heat in ‘combined heat and power’ applications or in combined-cycle gas turbine applications. As a result, SOFCs have various applications over a wide range of power from milliwatts to megawatts. This article provides an overview of SOFCs.
Author Keywords: Anode; Cathode; Electrolyte; Interconnect; Seal; Solid oxide fuel cells; System

34.
Improvement of (La0.74Bi0.10Sr0.16)MnO3–Bi1.4Er0.6O3 composite cathodes for intermediate-temperature solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 185, Issue 2, 1 December 2008, Pages 649-655
Junliang Li, Shaorong Wang, Xiufu Sun, Renzhu Liu, Xiaofeng Ye, Zhaoyin Wen
Abstract
Porous composite cathodes including (La0.74Bi0.10Sr0.16)MnO3−δ (LBSM) and Bi1.4Er0.6O3 (ESB) were fabricated and characterized using AC impedance spectroscopy. In our earlier work, the growth and aggregation of ESB particles were found in LBSM–ESB composite cathodes. In this study, therefore, two approaches were used to restrain the growth and aggregation of ESB particles. First, the sintering temperature of the composite cathode was reduced by introducing a sintering function layer, which caused a 22% reduction in the initial polarization resistance (R), but the cathode polarization resistance decreased at a rate of 2.15 × 10−4 Ω cm2 h−1 at 700 °C during a period of 100 h. Second, nano-sized Gd-doped ceria powder (CGO) was added to the composite cathode system. Stability improvement was achieved at 10 vol% CGO, and the degradation rate at 700 °C was 4.01 × 10−5 Ω cm2 h−1 during a period of 100 h.
Keywords: Intermediate-temperature solid oxide fuel cells; Cathode stability; Impedance spectroscopy; Composite cathode

35.
Electrochemical performance of (Bi2O3)1 − x(Er2O3) x–Ag composite material for intermediate temperature solid oxide fuel cell cathode Original Research Article
Solid State Ionics, Volume 179, Issues 27-32, 30 September 2008, Pages 1597-1601
Junliang Li, Shaorong Wang, Renzhu Liu, Zhengrong Wang, J.Q. Qian
Abstract
The electrochemical performance of ESB [(Bi2O3)1 − x(Er2O3) x]–Ag composite material for IT-SOFC cathode was studied on the SSZ [(ZrO2)0.89(Sc2O3)0.1(CeO2)0.01] electrolyte. The influence of different ESB/Ag ratio and erbium-doped content on the performance of the composite cathode was investigated using AC impedance spectroscopy analysis. The investigation showed that there was a low polarization resistance (0.16 Ω cm2 to 0.50 Ω cm2 at temperatures from 750 °C to 650 °C) when the content of 3ESB [(Bi2O3)0.7(Er2O3)0.3] and Ag was equal in composite cathode.
Keywords: SOFC; Cathode; Bismuth oxide; Composite material; Impedance

36.
Solid oxide fuel cell (SOFC) using industrial grade mixed rare-earth oxide electrolytes Original Research Article
International Journal of Hydrogen Energy, Volume 33, Issue 13, July 2008, Pages 3385-3392
Bin Zhu, Xiangrong Liu, Zhigang Zhu, Richard Ljungberg
Abstract
This work reports on solid oxide fuel cells (SOFCs) based on abundant natural resources of industrial grade mixed rare-earth carbonates and composites. The materials possessed natural compositions and nano-scale particles. The electrolytes made from these materials were able to achieve excellent fuel cell performances, 300–800 mW/cm2, at low temperatures (LT: 300–600 °C). Ionic transport mechanism, two-phase interface functions and composite role in electrolytes as well as resulted advanced fuel cell performances are discussed.
Keywords: Rare-earth mixed carbonates (LCP); LCP-oxide; LCP-oxide–carbonate-composites; Low temperature 300–600 °C; Solid oxide fuel cells

37.
(La0.74Bi0.10Sr0.16)MnO3−δ–(Bi2O3)0.7(Er2O3)0.3 composite cathodes for intermediate temperature solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 179, Issue 2, 1 May 2008, Pages 474-480
Junliang Li, Shaorong Wang, Zhengrong Wang, Renzhu Liu, Tinglian Wen, Zhaoyin Wen
Abstract
(La0.74Bi0.10Sr0.16)MnO3−δ (LBSM)–(Bi2O3)0.7(Er2O3)0.3(ESB) composite cathodes were fabricated for intermediate-temperature solid oxide fuel cells with Sc-stabilized zirconia as the electrolyte. The performance of these cathodes was investigated at temperatures below 750 °C by AC impedance spectroscopy and the results indicated that LBSM–ESB had a better performance than traditional composite electrodes such as LSM–GDC and LSM–YSZ. At 750 °C, the lowest interfacial polarization resistance was only 0.11 Ω cm2 for the LBSM–ESB cathode, 0.49 Ω cm2 for the LSM–GDC cathode, and 1.31 Ω cm2 for the LSM–YSZ cathode. The performance of the cathode was improved gradually by increasing the ESB content, and the performance was optimal when the amounts of LBSM and ESB were equal in composite cathodes. This study shows that the sintering temperature of the cathode affected performance, and the optimum sintering temperature for LBSM–ESB was 900 °C.
Keywords: Intermediate-temperature solid oxide fuel cells; Sintering temperature; Impedance spectroscopy; Composite cathode

38.
Composite cathode La0.15Bi0.85O1.5-Ag for intermediate-temperature solid oxide fuel cells Original Research Article
Materials Chemistry and Physics, Volume 108, Issues 2-3, 15 April 2008, Pages 290-295
Zhan Gao, Zongqiang Mao, Jianbing Huang, Ruifeng Gao, Cheng Wang, Zhixiang Liu
Abstract
Composites consisting of silver and lanthanum stabilized bismuth oxide (La0.15Bi0.85O1.5) were investigated as cathodes for intermediate-temperature solid oxide fuel cells with doped ceria as electrolyte. No stable phases were formed via reaction between La0.15Bi0.85O1.5 and Ag. The microstructure of the interfaces between composite cathodes and Ce0.8Sm0.2O1.5 electrolytes was studied by scanning electron microscopy after sintering at various temperatures. Impedance spectroscopy measurements revealed that the performance of cathode fired at 700 °C was the best. When the optimum fraction of Ag was 50 vol.%, polarization resistance values for the LSB-Ag50 cathode were as low as 0.14 Ω cm2 at 700 °C and 0.18 Ω cm2 at 650 °C. The steady-state polarization investigations on LSB and LSB-Ag50 cathodes were performed using typical three-electrode test cells in air. The results showed that the LSB-Ag50 composite cathode exhibited a lower overpotential and higher exchange current density than LSB, which indicated the electrochemical performance of LSB-Ag50 for the oxygen reduction reaction was superior to the LSB.
Keywords: Solid oxide fuel cells (SOFCs); Composite cathode; Lanthanum stabilized bismuth oxide (LSB); Samaria doped ceria (SDC)

39.
Synthesis and characterization of gadolinia-doped ceria–silver cermet cathode material for solid oxide fuel cells Original Research Article
Materials Chemistry and Physics, Volume 107, Issues 2-3, 15 February 2008, Pages 370-376
Pradyot Datta, Peter Majewski, Fritz Aldinger
Abstract
A series of Ce0.9Gd0.1O2−δ–Ag cermets with different Ag contents were prepared by conventional sintering process aiming at assessing the suitability of using them as cathode material for solid oxide fuel cell (SOFC) with Gadolinia-doped ceria electrolyte. The chemical compatibility between Ce0.9Gd0.1O2−δ (CGO) and Ag was investigated by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Thermal expansion coefficients of the cermets were measured as a function of Ag content and were found to increase with metallic content. Although oxygen adsorption at the surface of the cermets could be detected, no reaction or solid solubility between CGO and Ag was found.
Keywords: Oxide materials; Thermal expansion; Photoelectron spectroscopies; X-ray diffraction

40.
A high-performance Gd0.8Sr0.2CoO3–Ce0.9Gd0.1O1.95 composite cathode for intermediate temperature solid oxide fuel cell
Journal of Power Sources, Volume 176, Issue 1, 21 January 2008, Pages 102-106
Shouguo Huang, Chunqiu Peng, Zheng Zong
Abstract
Powders of Gd0.8Sr0.2CoO3 (GSC) were prepared by a glycine–nitrate process. Symmetrical cathodes of GSC–50Ce0.9Gd0.1O1.95 (GDC) (50:50 by volume) powders were deposited on GDC electrolyte pellets, and the electrochemical properties of the interfaces between the porous cathode and the electrolyte were investigated at intermediate temperature (500–750 °C) using electrochemical impedance spectroscopy. The addition of 50 vol.% GDC to GSC resulted in an additional factor ≈3 decrease in the area-specific resistance (ASR). The ASR values for the GSC–50GDC cathodes were as low as 0.064 Ω cm2 at 700 °C and 0.16 Ω cm2 at 600 °C, respectively. The maximum power density of a cell using the GSC–50GDC cathode was 356 mW cm−2 at 700 °C.
Keywords: Cathode; Solid oxide fuel cell; Area-specific resistance; Electrochemical impedance spectroscopy

41.
Zirconia Electrolyte-based Solid Oxide Fuel Cells
Encyclopedia of Materials: Science and Technology, 2008, Pages 9898-9902
S. C. Singhal
Abstract no available

42.
Thin films for micro solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 173, Issue 1, 8 November 2007, Pages 325-345
D. Beckel, A. Bieberle-Hütter, A. Harvey, A. Infortuna, U.P. Muecke, M. Prestat, J.L.M. Rupp, L.J. Gauckler
Abstract
Thin film deposition as applied to micro solid oxide fuel cell (μSOFC) fabrication is an emerging and highly active field of research that is attracting greater attention. This paper reviews thin film (thickness ≤1 μm) deposition techniques and components relevant to SOFCs including current research on nanocrystalline thin film electrolyte and thin-film-based model electrodes. Calculations showing the geometric limits of μSOFCs and first results towards fabrication of μSOFCs are also discussed.
Keywords: Thin film; Micro solid oxide fuel cell; Cathode; Anode; Electrolyte

43.
Development of Ag-(BaO)0.11(Bi2O3)0.89 composite cathodes for intermediate temperature solid oxide fuel cells
Journal of Power Sources, Volume 173, Issue 1, 8 November 2007, Pages 415-419
Shouguo Huang, Zheng Zong, Chunqiu Peng
Abstract
The electrochemical performances of Ag-(BaO)0.11(Bi2O3)0.89 (BSB) composite cathodes on Ce0.8Sm0.2O1.9 electrolytes have been investigated for intermediate temperature solid oxide fuel cells (ITSOFCs) using ac impedance spectroscopy from 500 to 700 °C. Results indicate that the electrochemical properties of these composites are quite sensitive to the composition and the microstructure of the cathode. The optimum BSB addition (50% by volume) to Ag resulted in about 20 times lower area specific resistance (ASR) at 650 °C. The ASR values for the Ag50-BSB and Ag cathodes were 0.32 and 6.5 Ω cm2 at 650 °C, respectively. The high performances of Ag-BSB cathodes are determined by the high catalytic activity for oxygen dissociation and ionic conductivity of BSB, and by the excellent catalytic activity for oxygen reduction of silver. The maximum power density of the Ag50-BSB cathode was 224 mWcm−2 at 650 °C, which classify this composite as a promising material for ITSOFC.
Keywords: Sintering; Electrical conductivity; Fuel cell materials; Composites; Cathode

44.
A review of numerical modeling of solid oxide fuel cells Review Article
International Journal of Hydrogen Energy, Volume 32, Issue 7, May 2007, Pages 761-786
Sadik Kakaç, Anchasa Pramuanjaroenkij, Xiang Yang Zhou
Abstract
The solid oxide fuel cell (SOFC) is one of the most promising fuel cells for direct conversion of chemical energy to electrical energy with the possibility of its use in co-generation systems because of the high temperature waste heat. Various mathematical models have been developed for three geometric configurations (tubular, planar, and monolithic) to solve transport equations coupled with electrochemical processes to describe the reaction kinetics including internal reforming chemistry in SOFCs. In recent years, considerable progress has been made in modeling to improve the design and performance of this type of fuel cells. The numbers of the contributions on this important type of fuels have been increasing rapidly. The objective of this paper is to summarize the present status of the SOFC modeling efforts so that unresolved problems can be identified by the researchers.
Keywords: Fuel cells; Solid oxide fuel cells (SOFCs); Fuel cell modeling; SOFC model review

45.
Electrolytes for solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 162, Issue 1, 8 November 2006, Pages 30-40
Jeffrey W. Fergus
Abstract
The high operating temperature of solid oxide fuel cells (SOFCs), as compared to polymer electrolyte membrane fuel cells (PEMFCs), improves tolerance to impurities in the fuel, but also creates challenges in the development of suitable materials for the various fuel cell components. In response to these challenges, intermediate temperature solid oxide fuel cells (IT-SOFCs) are being developed to reduce high-temperature material requirements, which will extend useful lifetime, improve durability and reduce cost, while maintaining good fuel flexibility. A major challenge in reducing the operating temperature of SOFCs is the development of solid electrolyte materials with sufficient conductivity to maintain acceptably low ohmic losses during operation. In this paper, solid electrolytes being developed for solid oxide fuel cells, including zirconia-, ceria- and lanthanum gallate-based materials, are reviewed and compared. The focus is on the conductivity, but other issues, such as compatibility with electrode materials, are also discussed.
Keywords: Solid oxide fuel cells; Electrolytes; Zirconia; Ceria; Gallates

46.
Novel compressive seals for solid oxide fuel cells Original Research Article
Journal of Power Sources, Volume 161, Issue 2, 27 October 2006, Pages 901-906
Shiru Le, Kening Sun, Naiqing Zhang, Maozhong An, Derui Zhou, Jingdong Zhang, Donggang Li
Abstract
Traditional seals for planar solid oxide fuel cells (pSOFCs) are rigid glass and glass–ceramic, which have caused the problem of being unable to replace malfunctioning components. Non-glass sealants have become a recent trend. In this paper, fumed silica-infiltrated alumina–silica fiber paper gaskets were investigated as a novel compressive seal for planar solid oxide fuel cells. The leak rates decreased with increase of the silica-infiltration amount and the compressive load. Samples pre-stressed at 10 MPa indicated far superior sealing characteristics, with leak rates as low as 0.04 sccm cm−1 at a 1 MPa compressive stress and a 10 kPa pressure gradient, and 0.05 sccm cm−1 for 0.05 MPa, and a 1.4 kPa pressure gradient.
Keywords: SOFC; Compressive seals; Ceramic fiber; Fumed silica

47.
Performance of intermediate temperature (600–800 °C) solid oxide fuel cell based on Sr and Mg doped lanthanum-gallate electrolyte Original Research Article
Journal of Power Sources, Volume 160, Issue 1, 29 September 2006, Pages 305-315
Wenquan Gong, Srikanth Gopalan, Uday B. Pal
Abstract
The solid electrolyte chosen for this investigation was La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM). To select appropriate electrode materials from a group of possible candidate materials, AC complex impedance spectroscopy studies were conducted between 600 and 800 °C on symmetrical cells that employed the LSGM electrolyte. Based on the results of the investigation, LSGM electrolyte supported solid oxide fuel cells (SOFCs) were fabricated with La0.6Sr0.4Co0.8Fe0.2O3–La0.9Sr0.1Ga0.8Mg0.2O3 (LSCF–LSGM) composite cathode and nickel–Ce0.6La0.4O2 (Ni–LDC) composite anode having a barrier layer of Ce0.6La0.4O2 (LDC) between the LSGM electrolyte and the Ni–LDC anode. Electrical performances of these cells were determined and the electrode polarization behavior as a function of cell current was modeled between 600 and 800 °C.
Keywords: Intermediate temperature solid oxide fuel cells; Materials system; Electrical performance

48.
Application of vacuum deposition methods to solid oxide fuel cells Review Article
Vacuum, Volume 80, Issue 10, 3 August 2006, Pages 1066-1083
L.R. Pederson, P. Singh, X.-D. Zhou
Abstract
The application of vacuum deposition techniques to the fabrication of solid oxide fuel cell (SOFC) materials and structures are reviewed, focusing on magnetron sputtering, vacuum plasma methods, laser ablation, and electrochemical vapor deposition. A description of each method and examples of use to produce electrolytes, electrodes, and/or electrical interconnects are given. Generally high equipment costs and relatively low deposition rates have limited the use of vacuum deposition methods in SOFC manufacture, with a few notable exceptions. Vacuum methods are particularly promising in the fabrication of micro-fuel cells, where thin films of high quality and unusual configuration are desired.
Keywords: Solid oxide fuel cell; Magnetron sputtering; Vacuum plasma deposition; Laser ablation; Electrochemical vapor deposition

49.
Oxide anode materials for solid oxide fuel cells Original Research Article
Solid State Ionics, Volume 177, Issues 17-18, July 2006, Pages 1529-1541
Jeffrey W. Fergus
Abstract
A major advantage of solid oxide fuel cells (SOFCs) over polymer electrolyte membrane (PEM) fuel cells is their tolerance for the type and purity of fuel. This fuel flexibility is due in large part to the high operating temperature of SOFCs, but also relies on the selection and development of appropriate materials — particularly for the anode where the fuel reaction occurs. This paper reviews the oxide materials being investigated as alternatives to the most commonly used nickel–YSZ cermet anodes for SOFCs. The majority of these oxides form the perovskite structure, which provides good flexibility in doping for control of the transport properties. However, oxides that form other crystal structures, such as the cubic fluorite structure, have also shown promise for use as SOFC anodes. In this paper, oxides are compared primarily in terms of their transport properties, but other properties relative to SOFC anode performance are also discussed.
Keywords: Solid oxide fuel cells; Anode; Perovskite; Fluorite

50.
Thermal cycle stability of a novel glass–mica composite seal for solid oxide fuel cells: Effect of glass volume fraction and stresses Original Research Article
Journal of Power Sources, Volume 152, 1 December 2005, Pages 168-174
Yeong-Shyung Chou, Jeffry W. Stevenson, Prabhakar Singh
Abstract
A novel glass–mica composite seal was developed based on a previously reported concept of “infiltrated” mica seals for solid oxide fuel cells. Ba–Al–Ca silicate sealing glass powder and Phlogopite mica flakes were mixed at glass volume fractions of 10–50 vol.% to make the glass–mica composite seals. The seals were leak tested for short-term thermal cycle stability as a function of glass volume fraction. Composite seals with 10 and 20 vol.% glass were also leak tested under compressive stresses from 3 to 100 psi and helium pressures of 0.2 or 2 psi. Post-mortem microstructure analyses were used to characterize the fracture (leak path) of the glass–mica composite seals and were related to the high temperature leakages. Open circuit voltage tests on dense 8YSZ electrolyte with the glass–mica composite seal showed very good thermal cycle stability over 250 cycles with minute (<1%) voltage drop. Keywords: Compressive seal; Mica; Leak test; Thermal cycle; SOFC

51.
Novel infiltrated Phlogopite mica compressive seals for solid oxide fuel cells Original Research Article Journal of Power Sources, Volume 135, Issues 1-2, 3 September 2004, Pages 72-78 Yeong-Shyung Chou, Jeffry W. Stevenson Abstract A novel compressive Phlogopite mica seal was developed that showed superior thermal cycle stability with very low leak rates at 800 °C. A commercially available Phlogopite mica paper was infiltrated with a wetting or melt-forming agent, and tested in a hybrid form during thermal cycling. The results of H3BO3-infiltrated mica showed a continued decrease in leak rates over thermal cycling, and very low rates (<5×10−4 sccm/cm) were obtained after 15 thermal cycles. The results of Bi-nitrate infiltrated mica exhibited a constant leak rate of (1–4)×10−3 sccm/cm over 36 thermal cycles. The leak rates of the infiltrated mica were one to two orders of magnitude lower than leak rates for the as-received micas. Open circuit voltage tests were also conducted using dense 8YSZ plates to assess the effectiveness of the mica seals. Open circuit voltages equivalent to, or close to, the theoretical (Nernst) values were obtained. Author Keywords: Thermal cycling; Compressive seal; Phlogopite mica; Leak rate; Open circuit voltage

52.
Solid oxide fuel cells operating without using an anode material Original Research Article Solid State Ionics, Volume 168, Issues 1-2, 15 March 2004, Pages 23-29 Daisuke Hirabayashi, Atsuko Tomita, Manuel E. Brito, Takashi Hibino, Ushio Harada, Masahiro Nagao, Mitsuru Sano Abstract We proposed a new type of solid oxide fuel cell (SOFC) operating without using an anode material, where the anode was spontaneously formed by reduction of the electrolyte surface under reducing gas conditions. A BaCe0.76Y0.20Pr0.04O3−α electrolyte most successfully met this criterion. This material showed high mixed protonic–electronic conduction, whereas the open circuit voltage (OCV) of the cell was slightly lower than the theoretical value. The resulting SOFC exhibited reasonable fuel cell performances together with a good stability to thermal and redox cyclings and high resistance to carbon deposition up to 800 °C for dry methane, ethane, and propane. Author Keywords: Solid oxide fuel cells; BaCe0.76Y0.20Pr0.04O3−α; Anode material

53.
A simple bilayer electrolyte model for solid oxide fuel cells Original Research Article
Solid State Ionics, Volume 158, Issues 1-2, February 2003, Pages 29-43 S. H. Chan, X. J. Chen, K. A. Khor Abstract A simple electrolyte model for bilayer ion-conducting membrane used in solid oxide fuel cell (SOFC) was developed. The model considers yttria-doped bismuth oxide (YDB) and gadolinia-doped ceria (GDC) as the substrate electrolyte, both coated with a thin layer of yttria-stabilized zirconia (YSZ) on the anode side. Migration of oxygen ions and diffusion of free electrons and electron holes through the bilayer electrolyte form the basis of modeling in this study. Results showed that depositing a very thin layer of YSZ onto the substrate electrolyte in the thickness ratio of 1 to 10,000 could increase the interfacial oxygen partial pressure significantly in the bilayer electrolyte and reduce the penetration of electronic current. The improved interfacial oxygen partial pressure by YSZ coating, higher than the equilibrium partial pressure of Bi/Bi2O3, made bismuth oxide a possible candidate for use in SOFC. An important result of the electronic blocking effect with bilayer electrolyte SOFC is to improve the open circuit voltage and thus to enhance the output power density of the cell. Author Keywords: Solid oxide fuel cell; Bilayer electrolyte; Interfacial oxygen partial pressure; Electronic blocking

54.
Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy Renewable and Sustainable
Energy Reviews, Volume 6, Issue 5, October 2002, Pages 433-455 A. Boudghene Stambouli, E. Traversa Abstract The generation of energy by clean, efficient and environmental-friendly means is now one of the major challenges for engineers and scientists. Fuel cells convert chemical energy of a fuel gas directly into electrical work, and are efficient and environmentally clean, since no combustion is required. Moreover, fuel cells have the potential for development to a sufficient size for applications for commercial electricity generation. This paper outlines the acute global population growth and the growing need and use of energy and its consequent environmental impacts. The existing or emerging fuel cells’ technologies are comprehensively discussed in this paper. In particular, attention is given to the design and operation of Solid Oxide Fuel Cells (SOFCs), noting the restrictions based on materials’ requirements and fuel specifications. Moreover, advantages of SOFCs with respect to the other fuel cell technologies are identified. This paper also reviews the limitations and the benefits of SOFCs in relationship with energy, environment and sustainable development. Few potential applications, as long-term potential actions for sustainable development, and the future of such devices are discussed. Author Keywords: Energy; Environment; Solid Electrolytes; Electrodes

55.
Reduction in the operating temperature of solid oxide fuel cells—potential use in transport applications Original Research Article
Annales de Chimie Science des Matériaux, Volume 26, Issue 4, July-August 2001, Pages 49-58 Michel Cassir, Emmanuel Gourba Abstract The development of solid oxide fuel cells (SOFC) offers new perspectives, in particular as auxiliary power units for vehicle applications. The elaboration of thin electrolyte layers is the main challenge in order to reduce their operating temperature. A brief review of the deposition techniques and of the potential electrolytes is presented. A relatively new technique, Atomic Layer Deposition (ALD), allows to produce thin, dense and homogeneous layers, i.e. zirconia or zirconia-based thin layers can be deposited on different substrates. The interest of elaborating bi- or multi-layer electrolytes is outlined.

56.
High-temperature superconductor materials for contact layers in solid oxide fuel cells: II. Chemical properties at operating temperatures Original Research Article
Acta Materialia, Volume 49, Issue 11, 22 June 2001, Pages 1987-1992 I. Arul Raj, F. Tietz, A. Gupta, W. Jungen, D. Stöver Abstract The chemical reactivity between superconducting ceramic materials (YBa2Cu3O7−x, Bi2Sr2CaCu2O8+x and Bi2Sr2CuO6+x) and the cathode material of solid oxide fuel cells (La0.65Sr0.3MnO3) was investigated by long-term annealing experiments of pressed powder mixtures lasting two weeks at 850°C. The chemical properties at the operating temperature of a solid oxide fuel cell revealed that all three superconducting materials reacted with La0.65Sr0.3MnO3 and underwent changes in volume and density after annealing. The chemical compatibility between the superconductors and interconnect material, a ferritic steel (X 10 CrAl 18), was investigated using screen-printed thick layers of Bi2Sr2CuO6+x on steel substrates. The formation of undesirable products, especially SrCrO4, due to diffusion processes across the interface was confirmed by investigations of metallographic cross-sections. Efforts to stop the interfacial reaction by introducing a thin CuO barrier layer between the superconductor and steel did not solve the problem. Author Keywords: Superconductors; Steel; Chemical; Corrosion; Solid oxide fuel cells

57.
High-temperature superconductor materials for contact layers in solid oxide fuel cells: I. Sintering behavior and physical properties at operating temperatures Original Research Article Acta Materialia, Volume 49, Issue 5, 14 March 2001, Pages 803-810 F. Tietz, I. Arul Raj, W. Jungen, D. Stöver Abstract The superconducting materials Bi2Sr2CaCu2O8+x, and Bi2Sr2CuO6+x were identified as possible candidates for contact layer materials between the perovskite-type ceramic cathode and the metallic interconnector for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The two compounds were synthesized by solid-state reaction and citrate complexation techniques. Densification experiments were performed in air at different temperatures. It was found that the pressed pellets fabricated from both the phases had undergone shape changes due to swelling at temperatures above 800°C. Since the processes of volume expansion and crystallization were found to compete with the sintering process, it was expected to be very difficult to achieve compact layers from these materials. The conductivity measurements indicated metallic behavior of both phases and rather low conductivity values for application as a contact layer in IT-SOFC. Dilatometric experiments were also carried out on these materials to measure their thermal expansion coefficients. The properties of commercial-grade YBa2Cu3O7−x were also investigated for comparison. Author Keywords: Superconductors; Sintering; Electrical conductivity; Thermal expansion; Solid oxide fuel cells

58.
Advances in solid oxide fuel cell technology Original Research Article
Solid State Ionics, Volume 135, Issues 1-4, 1 November 2000, Pages 305-313 S. C. Singhal Abstract High temperature solid oxide fuel cells (SOFCs) offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. These fuel cells provide many advantages over traditional energy conversion systems including high efficiency, reliability, modularity, fuel adaptability, and very low levels of NOx and SOx emissions. Furthermore, because of their high temperature of operation ( 1000°C), natural gas fuel can be reformed within the cell stack eliminating the need for an expensive, external reformer. Also, pressurized SOFCs can be successfully used as replacements for combustors in gas turbines; such hybrid SOFC–gas turbine power systems are expected to reach efficiencies over 70%. This paper reviews the materials and fabrication methods used for the different cell components, and discusses the performance of cells fabricated using these materials; it also discusses the materials and processing studies that are under investigation to reduce the cell cost. Finally, the paper summarizes the recently built power generation systems that employed state-of-the-art SOFCs. A new design SOFC that combines the seal-less feature of tubular cells and a flattened air electrode with integral ribs is also described; this new design has a shortened current path and hence lower cell resistance and higher power output than tubular cells. Author Keywords: Fuel cells; Oxide; Electricity (power) generation; Performance; Electrolyte; Electrodes; Gas turbine; Cost Materials: ZrO2; Y2O3; Y2O3-stabilized ZrO2 (YSZ); LaMnO3; LaCrO3; Ni

59.
Fabrication of thin electrolytes for second-generation solid oxide fuel cells Original Research Article
Solid State Ionics, Volume 131, Issues 1-2, 1 June 2000, Pages 79-96 J. Will, A. Mitterdorfer, C. Kleinlogel, D. Perednis, L. J. Gauckler Abstract This paper reviews different thin-film deposition methods for oxides, especially for stabilized zirconia and compares them with regard to SOFC applications. These methods will be classified into chemical, physical methods and ceramic powder processes. Each method is described with its special technical features and examples of components for fuel cells are given. PVD and CVD methods are specially suited to depositing high-quality films of simple chemical compositions. Liquid droplet methods and ceramic powder processes are more qualified for the deposition of complicated chemical compositions. Author Keywords: SOFC; Thin films; Zirconia; PVD; CVD; Liquid precursor methods

60.
Solid oxide fuel cells: fundamental aspects and prospects Original Research Article Electrochimica Acta, Volume 45, Issues 15-16, 3 May 2000, Pages 2423-2435 Osamu Yamamoto Abstract Solid oxide fuel cells (SOFCs) are advanced electrochemical reactors operating at a high temperature. SOFCs are presently under development for a variety of electric power generation applications with high energy conversion efficiency. This paper reviews the science and technology of SOFCs with emphasis on discussion of their component materials.

61.
Testing tubular solid oxide fuel cells in nonsteady-state conditions Original Research Article Journal of Power Sources, Volume 79, Issue 2, June 1999, Pages 242-249 V. V. Kharton, E. N. Naumovich, V. N. Tikhonovich, I. A. Bashmakov, L. S. Boginsky, A. V. Kovalevsky Abstract Fabrication of tubular-type solid oxide fuel cells (SOFCs) with yttria-stabilized zirconia electrolyte, cathodes and current collectors of lanthanum–strontium manganite (LSM) is described. Particular emphasis is given to the techniques of producing LSM tubes by the isostatic pressing method, preparing oxide electrodes via cellulose precursor decomposition, and activation of SOFC electrodes by applying dispersed catalysts onto their surface. Coating nickel-cermet anodes with dispersed ceria and depositing praseodymium oxide onto manganite cathode surface was found to result in improving SOFC performance. Testing single cells with externally switched pulse load demonstrated a possibility to optimize the SOFC operating mode at a given resistance of the closing circuit by variation of the pulse period-to-pulse duration ratio of the pulses which open the circuit. No effect of the pulse load frequency on SOFC performance was observed in the frequency range from 2 Hz to 50 kHz. The results of testing SOFCs in nonsteady-state conditions suggest applicability of the externally switched pulse load to match resistances of single cells in the SOFC stacks. Author Keywords: SOFC; Pulse load; Surface modification; Lanthanum–strontium manganite; Cellulose precursor

62.
Solid oxide electrolyte fuel cell review Original Research Article
Ceramics International, Volume 22, Issue 3, 1996, Pages 257-265 S. P. S. Badwal, K. Foger Abstract Solid oxide fuel cells are a promising technology for electric power generation in the 21st century. The principles of SOFC operation, stack designs, materials, status of development and future challenges are discussed.

63.
Sputter-deposited medium-temperature solid oxide fuel cells with multi-layer electrolytes Original Research Article
Solid State Ionics, Volume 61, Issue 4, June 1993, Pages 273-276 L. S. Wang, S. A. Barnett Abstract The deposition, interfacial impedances, and characteristics of solid oxide fluel cells (SOFC) with thin-film multi-layer electrolytes are described. The cell layers — a 1 μm thick Ag---YSZ cermet cathode, a 15 to 20 μm thick Ni---YSZ anode — were deposited on porous alumina by reactive magnetron co-sputtering of metal tartgets in Ar---O2 mixtures. The effect of adding Y-stabilized Bi2O3 (YSB) and Y-doped CeO2 (YDC) layers at the ytria-stabilized-zirconia (YSZ) electrolyte surfaces was investigated. The open circuit voltage of the H2/H2O (3%), Ni---YSZ / electrolyte / Ag---YSZ, air fuel cells tested at 750°C was 0.78—0.85 V, less than expected theoretically, indicating some porosity in the electrolyte layers. The cell resistance was 4.5 Ω cm2 for a YSZ electrolyte, due mainly to the electrode interfacial resistances, and the maximum power density was 35 mW / cm2. Adding a 60 nm-thick YSB layer at the YSZ/Ag---YSZ interface reduced the air electrode resistance from ≈1.4 to 0.45 Ω cm2, leading to an increase in the maximum power density to ≈50 mV/cm2. Adding a 100 nm-thick YDC layer at the Ni---YSZ/ YSZ interface further increased the maximum power density to 110 mW/cm2 at a cell resistance of 1.6 μ cm2. The three-layer YSB/YSZ/YDC electrolyte thus resulted in a factor-of-three increase in power density over a YSZ electrolyte.

64.
LaMnO3 air cathodes containing ZrO2 electrolyte for high temperature solid oxide fuel cells Original Research Article
Solid State Ionics, Volume 57, Issues 3-4, October 1992, Pages 295-302 T. Kenjo, M. Nishiya Abstract This study is an attempt to improve LaMnO3 high temperature air cathodes by using an electrode structure which resembles that of porous electrodes of liquid electrolyte fuel cells. Y2O3-stabilized zirconia (YSZ) was loaded with LaMnO3 and molded into porous electrodes which had YSZ-LaMnO3 interfaces inside the electrodes. A strong relation was seen between the conductivity of YSZ added and polarization losses, suggesting that the internal LaMnO3-YSZ contacts are active for O2 reduction. The addition of YSZ prevents the formation of highly resistive La2Zr2O7 which has otherwise been formed at the electrode-electrolyte interface. This effect also helps to enhance the electrodes.

65.
A new solid oxide fuel cell design based on thin film electrolytes Original Research Article Energy, Volume 15, Issue 1, January 1990, Pages 1-9 S. A. Barnett Abstract A novel solid oxide fuel cell (SOFC) design that can be fabricated entirely using low-temperature, thin-film processing is described. Potential advantages of the cell are reduced materials costs and improved fuel-cell characteristics. The critical design feature is the use of thin (≈ 50 nm), catalytically-active oxide layers on a < 10 μm thick yttria-stabilized zirconia (YSZ) supported electrolyte to minimize reaction overpotentials and ohmic losses. Doped ceria at the fuel electrode side and doped bismuth oxide at the oxygen electrode side are proposed for the surface layers. The surface reaction rates and overall electrolyte conductance in this design are high enough at < 750 °C to allow efficient SOFC operation. This operating temperature is low enough that low-resistance, thin-film metal electrodes, Ni at the fuel side and Ag at the oxygen side, can be used to provide low ohmic losses. The overpotential behavior of the proposed cell is estimated on the basis of literature data and leads to fuel efficiencies > 50% at a power density of ≈ 0.5 W/cm2 when operated at 750 °C. The thin film monolithic design will lead readily to the incorporation of the cells into stacks with high power-to-weight and power-to-volume ratios. Methods for cell fabrication are discussed.

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