Ceria Interlayer Research Articles

Cathode-supported SOFC using a highly conductive lanthanum aluminate-based electrolyte

A newly-developed, highly conductive, and cost-effective LaAlO 3-based perovskite was used as a solid electrolyte to replace costly LaGaO 3 in this study. The La 0.9Ba 0.1Al 0.9Y 0.1O 3 (LBAYO) solid electrolyte was fabricated by codoping 10 at.% Ba and 10 at.% Y into the cation sublattice of LaAlO 3. The conductivity of the doubly doped La 0.9Ba 0.1Al 0.9Y 0.1 O 3 was enhanced to 184 × 10 − 4 S cm − 1 which is about 50 times higher than that of the undoped one at 800 °C. Cathode-supported cells consisting of Ni/yttria-stabilized zirconia (Ni/YSZ) anode, a thin LBAYO electrolyte (~ 63 μm), a samarium doped ceria (SDC) interlayer, and a lanthanum strontium manganite (LSM) cathode were assembled and tested. The LBAYO electrolyte film was first prepared on conductive LSM substrates using the electrophoretic deposition (EPD) technique. The cathode-supported structure, consisting of an LBAYO film on a porous LSM substrate, was co-fired at 1450 °C for 2 h. A crack-free LBAYO film with a uniform thickness supported on a porous LSM substrate was obtained. Subsequently, a 10 μm-thick SDC buffer interlayer between the electrolyte and 30 μm-thick NiO/YSZ anode was screen-printed and fired on the electrolyte film. A 10-day test showed essentially no degradation on the output power from the cell using the LBAYO electrolyte. These tests convincingly demonstrated the feasibility of an SOFC using LBAYO as the electrolyte when operated at temperatures ranging from 600 °C to 800 °C.

Low temperature deposited (Ce,Gd)O2−x interlayer for La0.6Sr0.4Co0.2Fe0.8O3 cathode based solid oxide fuel cell

Application of La0.6Sr0.4Co0.2Fe0.8O3 perovskites cathode in solid oxide fuel cell (SOFC) can benefit from its high electrocatalytic activity at 600–800°C. However, due to the chemical and mechanical incompatibility between the LSCF cathode and state-of-the-art yttria stabilized zirconia (YSZ) electrolyte, a ceria-based oxide barrier interlayer is usually introduced. In this work, gadolinia doped ceria (GDC) interlayers are prepared by screen printing (SP), electron beam evaporation (EB) and ion assisted deposition (IAD) methods. The microstructures of the GDC interlayers show great dependence on the deposition methods. The 1250°C-sintered SP interlayer exhibits a porous microstructure. The EB method generates a thin and compact interlayer at a low substrate temperature of 250°C. With the help of additional energetic argon and oxygen ions bombardment on the deposited species, the IAD method yields the densest GDC interlayer at the same substrate temperature, which leads to the best electrochemical performance of LSFC-based SOFC.

Temperature and Bias Effects on Sputtered Ceria Diffusion Barriers for Solid Oxide Fuel Cells

The effects of both temperature and applied bias power during the sputtering of gadolinia-doped ceria (GDC) interlayers used as diffusion barriers in anode-supported solid oxide fuel cells (SOFCs) were studied. Scanning electron microscopy analysis revealed that increasing the applied bias power, in the 0–300 W range, increasingly promotes the deposition of continuous and dense interlayers. Such feature was mirrored in the electrochemical performance of single cells that exhibited enhancement of the power density of an SOFC with bias-assisted sputtered interlayers. In addition, fuel cells having interlayers deposited in the temperature range exhibited similar microstructure and electrochemical performances, indicating that the applied bias allows for the sputtering of GDC protective interlayers at relatively lower temperatures than unbiased depositions. The presented results evidenced that bias-assisted sputtering is an effective technique for the fabrication of high performance anode-supported SOFCs.

Sr 2Fe 4/3Mo 2/3O 6 as anodes for solid oxide fuel cells

Sr 2Fe 4/3Mo 2/3O 6 has been synthesized by a combustion method in air. It shows a single cubic perovskite structure after being reduced in wet H 2 at 800 °C and demonstrates a metallic conducting behavior in reducing atmospheres at mediate temperatures. Its conductivity value at 800 °C in wet H 2 (3% H 2O) is about 16 S cm −1. This material exhibits remarkable electrochemical activity and stability in H 2. Without a ceria interlayer, maximum power density ( P max) of 547 mW cm −2 is achieved at 800 °C with wet H 2 (3% H 2O) as fuel and ambient air as oxidant in the single cell with the configuration of Sr 2Fe 4/3Mo 2/3O 6|La 0.8Sr 0.2Ga 0.83Mg 0.17O 3 (LSGM)| La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF). The P max even increases to 595 mW cm −2 when the cell is operated at a constant current load at 800 °C for additional 15 h. This anode material also shows carbon resistance and sulfur tolerance. The P max is about 130 mW cm −2 in wet CH 4 (3% H 2O) and 472 mW cm −2 in H 2 with 100 ppm H 2S. The cell performance can be effectively recovered after changing the fuel gas back to H 2.

Increased Cathodic Kinetics on Platinum in IT-SOFCs by Inserting Highly Ionic-Conducting Nanocrystalline Materials

One of the crucial factors for improving intermediate-temperature solid oxide fuel cell (SOFC) performance relies on the reduction in the activation loss originating from limited electrode reaction kinetics. We investigated the properties and functions of the nanocrystalline interlayer via quantum simulation and electrochemical impedance analyses. Electrode impedances were found to decrease several folds as a result of introducing a nanocrystalline interlayer and this positive impact was the most significant when the interlayer was a highly ionic-conducting nanocrystalline material. Both exchange current density and maximum power density were highest in the ultrathin SOFCs (fabricated with microelectromechanical systems (MEMS) compatible technologies) consisting of a 50 nm thick nano-gadolinia doped ceria (GDC) interlayer. Oxygen vacancy formation energies both at the surface and in the bulk of pure zirconia, ceria, yttria-stabilized zirconia, and GDC were computed from density functional theory, which provided insight on surface oxygen vacancy densities.

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells: II. Role of Ni Diffusion on LSM Performance

The sintering of (LSM-20) solid oxide fuel cell cathodes (in the temperature range of ) on anode-supported cells utilizing a Ni–yttria-stabilized zirconia (YSZ) anode and a thin YSZ electrolyte ( thickness) revealed the need for a protective ceria interlayer to prevent a detrimental interaction between the YSZ and the LSM. The interaction, however, was not the typically assumed formation of insulating La- and Sr-zirconate, but rather the result of Ni diffusion from the anode through the YSZ electrolyte and into the LSM, resulting in coarsening and increased densification of the LSM microstructure. The protective layers at the cathode/electrolyte interface were effective in blocking the Ni diffusion. As an alternative to the use of a protective ceria interlayer, the presence of YSZ in the cathode material was able to suppress the coarsening of LSM, thereby significantly improving the electrochemical performance.

Properties of bias-assisted sputtered gadolinia-doped ceria interlayers for solid oxide fuel cells

The growth and electrochemical properties of gadolinia-doped ceria (GDC) interlayers deposited by bias-assisted magnetron sputtering in solid oxide fuel cells have been investigated. Such interlayers act as diffusion barriers to protect the yttria-stabilized zirconia electrolyte, preventing possible degradation when mixed ionic–electronic conductor (La,Sr)(Co,Fe)O 3− δ is used as the cathode. The dependence of the applied bias during the sputtering deposition on both the interlayer microstructure and fuel cell performance has been studied in anode-supported single cells. The main experimental results showed that bias-assisted sputtering of GDC interlayers produced microstructures denser than those of unbiased depositions, which resulted in increased electrochemical properties of fuel cells.

Bias-Assisted Sputtering of Gadolinia-Doped Ceria Interlayers for Solid Oxide Fuel Cells

The effects of both temperature and applied bias power during the sputtering of gadolinia-doped ceria (GDC) interlayers used as diffusion barriers in anode-supported solid oxide fuel cells (SOFC) were investigated. Scanning electron microscopy analysis revealed that increasing the applied bias power, in the 0-300W range, progressively inhibits the columnar structure typically observed in sputtered films, favoring the deposition of dense interlayers. Such feature was mirrored in the electrochemical tests of single cells that demonstrated enhanced power density for SOFC with bias-assisted sputtered interlayers. In addition, similar electrochemical performances of fuel cells having interlayers deposited in the 400-800 {degree sign}C temperature range indicated that the applied bias allows for the sputtering of GDC protective interlayers at relatively lower temperatures than unbiased depositions. The presented results evidenced that bias-assisted sputtering is an effective technique for the fabrication of high-performance anode supported SOFC.

Property change of a LaNi 0.6Fe 0.4O 3 cathode in the initial current loading process and the influence of a ceria interlayer

We prepared single cells with a LaNi 0.6Fe 0.4O 3 (LNF) cathode and a 0.89ZrO 2–0.10Sc 2O 3–0.01Al 2O 3 (SASZ) electrolyte sheet with a Ce 0.8Sm 0.2O 2 (SDC) interlayer deposited by the spin-coating an organometallic solution. We investigated the influence of this SDC interlayer on the initial cathode properties. We found that the SDC interlayer as thin as 30 nm effectively reduces the initial cathode interface resistance, improves the initial cathode performance, and shortens the current loading time needed to reach a steady operating condition when the cathode sintering temperature is 1100°C or lower. X-ray diffraction analysis revealed that the migration of Zr atoms from the SASZ electrolyte to the SDC interlayer is not significant when the sintering temperature is 1100°C or lower. However, the Zr atoms penetrated the spin-coated SDC interlayer and reacted with the LNF to form La 2Zr 2O 7,when the sintering temperature is 1150°C or higher.

Interface Stability of Perovskite Cathodes and Rare-Earth Doped Ceria Interlayer in SOFCs

The reaction and interdiffusion characteristics at the interface of rare-earth doped ceria (, M = Gd, La) and perovskite-type cathode materials (, and ) were investigated and their effect on the long-term reliability of solid oxide fuel cell (SOFC) performance are discussed. Secondary phase formation was observed at the ceria side of the interface by the reaction of the rare-earth component in ceria and transition metal components in perovskite. A significant diffusion of transition metals (cobalt or iron) and strontium from perovskite to ceria was observed. The iron content in perovskite and the type of rare earth in ceria strongly affect the stability of secondary phase and extent of transition metal diffusion in ceria. The bulk diffusivity was determined as a function of temperature. The iron component exhibited a fast and inhomogeneous migration in ceria, forming the iron-rich inclusions. The strontium component exhibited the tendency of the fast grain boundary diffusion in ceria. The effects of mass transport on the SOFC materials durability are discussed.

Alanine Assisted Low-Temperature Synthesis and Characterization of Nanocrystalline SOFC Cathodes

Nanocrystalline SOFC cathode materials of perovskite family, La1-xSrxM1-yCoyO3, where 0<x{less than or equal to}0.5, 0<y {less than or equal to}0.8 (M is transitional metal= Mn or Fe) have been synthesized at a relatively low temperature by combustion technique using alanine as novel fuel. The thermal analyses of the precursor gels show sharp single step combustion with low decomposition temperature (170- 200oC). Detailed X-ray powder diffraction analyses show 47-96% phase purity in the as-synthesized powder and upon calcination at temperature ~ 825oC, single phase material is obtained wherein the nanocrystallinity (crystallite size ~19-24 nm) is retained. Densification studies of the materials are carried out within 900-1100oC. The coefficient of thermal expansion (CTE) of the sintered cathodes is also measured. Detailed electrical characterizations of the sintered cathodes are evaluated and correlated with the microstructures. The electrochemical performances of SOFC single cells (Ni-YSZ anode-support /YSZ ~ 20 μm/LaFeO3-based cathodes) with ceria interlayer show high current density of ~1.2 A/cm2 at 0.7V at 8000C.

Development of Tubular Solid Oxide Fuel Cells Composed of Ni-YSZ Supported SSZ Electrolyte Film and Cobaltile Electrodes for Reduced-Temperature Operating SOFCs

Tubular solid oxide fuel cells (SOFCs) composed of Ni- yttria- stabilized zirconia (YSZ) supported scandia-stabilized zirconia (SSZ) electrolyte film, doped ceria interlayer and strontium-doped cobaltile electrodes were successfully developed for reduced-temperature operation. The SOFCs were fabricated by adopting a slurry coating technique, which allows to prepare a ceramic layer with a thickness varied between 1~ca. 150μm, and a co-fire process. The fabrication process was investigated in detail for realizing low cost SOFCs with high degree of straight, round, high reproductive quality, and high electrochemical performance. Flawless dense electrolyte thin film less than 10μm was achieved on porous tubular Ni-YSZ substrate with the thickness that thicker than 500μm. Primary results of electrochemical performance test show that the a fabricated cells with (Sm0.6Sr0.4)CoO3 electrode could produce ca. 0.4 Wcm-2 of power density at H2 utilization of 60% at 800oC.

Preparation of SDC Interlayer and Influence on Performances of Anode Supported Solid Oxide Fuel Cells

A single cell with a two-layer electrolyte consisting of an yttria stabilized zirconia (YSZ, Y2O3 8 mol%) layer and an Sm-doped ceria (SDC, Sm2O3 20mol%) interlayer has been fabricated on porous YSZ-NiO anode support. The layer of YSZ electrolyte was prepared by modified electrostatic powder coating method and the SDC interlayer by screen-printed method on the green YSZ layer. After co-firing at 1400°C for 5 h, the two-layer film with a dense YSZ film of about 15μm and porous SDC film of about 25μm was fabricated. The performances of as-fabricated single cell using La0.8Sr0.2FeO3 as cathode were tested using H2-3% H2O as fuel and air as oxidant at 800°C. Results indicated that the peak power density of a single cell with SDC interlayer reaches 469 mW/cm2 at 800°C, obviously higher than that of without SDC interlayer, which is about 300 mW/cm2 at 800°C.

Application of ( Sm0.5Sr0.5 ) CoO3 as a Cathode Material to ( Zr , Sc ) O2 Electrolyte with Ceria-Based Interlayers for Reduced-Temperature Operation SOFCs

Application of as a cathode material on electrolyte for reduced-temperature operation solid oxide fuel cells (SOFCs) was investigated in detail. As a protective layer for preventing the unfavorable solid-state reactions between materials, doped ceria thin films with an apparent density range between 50 and 80% were fabricated on the electrolyte by a cost-effective wet ceramic process using nanometer and submicrometer powders. The impact of doped ceria interlayers on the performance of cathode was investigated by X-ray diffraction and ac impedance measurements. It was found that controlling the microstructure of interlayers is important for cathodic performance. The cathode deposited on electrolyte coated by or interlayer can reach an interface conductivity of 4.4 or , respectively, at .

Resistance of (La,Sr)CoO3/YSZ Interface with a Ceria Interlayer

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Resistance of (La, Sr)CoO3 / YSZ Interface with a Ceria Interlayer

Electrochemical impedance of dense (La,Sr)CoO, (LSCO) electrode on single crystalline YSZ electrolyte was investigated in order to clarify the effect of ceria interlayer. Pulsed laser deposition technique was used to fabricate a dense LSCO electrode (∼1.5 pm) and a thin (∼100 nm) Ce 0.9 Gd 0.1 O 1.95 (CGO) interlayer on a (1 0 0) surface of YSZ. Unlike the direct contact of LSCO on YSZ, LSCO/CGO/YSZ interface showed no significant degradation during the operation. The main part of the resistance was attributed to oxygen exchange reaction at the electrode surface as the case of LSCO electrode on CGO electrolyte. However, a possible minor contribution of the interface resistance was revealed by equivalent circuit analysis. The interface impedance was a single depressed semicircle, in most cases, in a complex impedance plane. It did not depend strongly on oxygen potential and temperature. It ranged from 0.3 to 1 Ωcm -2 , which may be significant in a practical porous electrode with smaller contact area.

Application of (Sm0.5 Sr0.5)CoO3 to (Zr, Sc)O2 Electrolyte SOFCs for Reduced Temperature Operation

Application of (Sm 0.5 Sr 0.5 )CoO 3 (SSC) as a cathode material on Zr 0.89 Sc 0.1 Ce 0.01 O 1.95 electrolyte for reduced temperature operation SOFCs was investigated in detail. As a protective layer for the electrolyte, doped ceria thin films were fabricated on the electrolyte by a cost effective wet ceramic process using nanometer Ce 0.8 Sm 0.2 O 1.9 and submicrometer Ce 0.9 Gd 0.1 O 1.95 powders. The impact of doped ceria interlayer on the performance of (Sm 0.5 Sr 0.5 )CoO 3 cathode was investigated by XRD and AC impedance measurements. It was found that controlling the microstructure of the interlayer is important for (Sm 0.5 Sr 0.5 )CoO 3 cathodic performance. The SSC cathode deposited on SSZ electrolyte coated by (Ce 0.8 Sm 0.2 )O 1.9 or (Ce 0.9 Gd 0.1 )O 1.95 interlayer can reach an interface conductivity of 4.4 S/cm 2 or 7.2 S/cm 2 at 700°C, respectively.

Preparation and evaluation of doped ceria interlayer on supported stabilized zirconia electrolyte SOFCs by wet ceramic processes

We have fabricated anode-supported solid oxide fuel cells (SOFCs) for reduced temperature operation by wet ceramic processes. Nickel/yttria-stabilised ZrO 2 (Ni-YSZ), nickel/scandia-stabilised ZrO 2 (Ni-ScSZ) cermets, ScSZ, gadolinia-doped ceria (GDC), and strontium-doped LaCoO 3 (LSCO) were used as materials for anode substrate, anode functional layer, electrolyte, interlayer, and cathode, respectively. The influences of firing temperature of GDC films to the characteristics of ScSZ/GDC interface were investigated in detail using XRD and AC impedance spectroscopy; 1200 °C was considered as the optimum firing temperature of GDC film on ScSZ electrolyte. By combining the ScSZ electrolyte film with GDC interlayer, we succeeded in preventing the solid-state reactions between ScSZ and LSCO. The anode-supported SOFCs with GDC interlayer fired at 1200 °C generated electricity successfully at reduced temperature. However, in the case of SOFCs, with whole functional layers cofired together at 1200 °C, the performances of the cell were badly affected by the contact between ScSZ and GDC films. Further investigation for matching the sintering behaviors of ScSZ and GDC green films are required to realize a cost-effective cofiring process for fabricating the anode-supported SOFCs employing CGO interlayer.

La(Sr)FeO3SOFC Cathodes with Marginal Copper Doping

Abstract (La0.8Sr0.2)0.98Fe0.98Cu0.02O3-δ can be sintered directly onto YSZ (without the need for a protective ceria interlayer to prevent inter-diffusion). Though subject to an extended “burn-in” period (~200 hours), anode-supported YSZ cells utilizing the Cu-doped LSF achieve power densities ranging from 1.3-1.7 W/cm2 at 750oC and 0.7V. These cells have also demonstrated 500 hours of stable performance. The results are somewhat surprising given that XRD indicates an interaction between (La0.8Sr0.2)0.98Fe0.98Cu0.02O3-δ and YSZ resulting in the formation of strontium zirconate and/or monoclinic zirconia. The amount and type of reaction product was found to be dependent on cathode and electrolyte powder pre-calcination temperatures.

Interaction between La(Sr)FeO 3 SOFC cathode and YSZ electrolyte

Anode-supported yttria-stabilized zirconia (YSZ) solid oxide fuel cells utilizing a Sr-doped LaFeO 3 (LSF) cathode show improved performance with the incorporation of a Sm-doped CeO 2 layer between the cathode and YSZ electrolyte. Detailed X-ray diffraction (XRD) analysis of LSF–YSZ reaction mixtures indicates no strontium or lanthanum zirconate formation between these materials even at 1400 °C. However, a significant shift in the LSF diffraction peaks is readily apparent and corresponds to a unit cell volume expansion. The most likely scenario for the change in volume is considered to be the incorporation of Zr 4+ cations in the perovskite structure. The presence of the Zr cations subsequently results in reduced electrical conductivity of the cathode, potentially explaining the need for the aforementioned ceria interlayer.