LSGM Electrolyte Research Articles

Evaluation of La2Ni1−xCoxO4±δ as a SOFC Cathode Material

Recent work has identified fast oxide ion conductivity in the K2NiF4 structured oxides. In particular, the La2NiO4+δ material has been found to possess diffusion coefficients comparable with the known perovskite cathode materials. Coupled with the reasonable electronic conductivity of ~ 100 Scm−1 at 650°C, these materials would appear to be promising candidates for new SOFC cathodes.Preliminary measurements of the La2NiO4+δ composition as a symmetrical cell on a CGO electrolyte indicated that the overall performance was below that expected from the Adler model. Subsequent work has been carried out by Bassat and co-workers investigating the Ln2NiO4+δ materials (Ln = La, Nd, Pr) on an YSZ electrolyte. The work reported here investigated La2Ni1−xCoxO4±δ cathodes on both CGO and LSGM electrolytes and compared the ASR data from a series of compositions. It has been found that the materials deposited on LSGM gave the best ASR data.

Plasma Sprayed LSGM Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells

A strontium-and-magnesium-doped lanthanum gallate (LSGM) electrolyte was processed into a thick film ranging from 100 - 550 μm using a plasma spray technique, followed by post heat-treatment at elevated temperatures (500 - 800°C). The processed LSGM electrolyte was characterized in terms of its (1) physical properties including phase purity, crystallinity, density, and (2) electrochemical properties, including open circuit voltage, ionic conductivity, and ac impedance. The electrochemical properties of the plasma sprayed LSGM were also compared with press-and-sintered LSGM pellets. The as-sprayed electrolyte exhibited a single LSGM phase in a mixture of amorphous and crystalline states. The amorphous phase can completely transform into a crystalline phase at temperatures up to 800°C as revealed by the XRD and impedance studies. The successful processing of LSGM using an industrial plasma spray technique offers a potential opportunity for fabrication of solid oxide fuel cells (SOFCs) for intermediate temperature applications (500 - 800°C).

Extruded Tubular Strontium- and Magnesium-Doped Lanthanum Gallate, Gadolinium-Doped Ceria, and Yttria-Stabilized Zirconia Electrolytes: Mechanical and Thermal Properties

Thermal properties and mechanical strength of ceramic fuel-cell components are critical in allowing for rapid start-up and operational stability at high temperatures of solid oxide fuel cell (SOFC) systems. Tubular SOFC electrolytes were prepared using a plastic extrusion technique from a dough containing the electrolyte powders and additives. Strontium- and magnesium-doped lanthanum gallate (LSGM), gadolinium-doped ceria (CGO), and 8 mol % yttria-stabilized zirconia (YSZ) were studied. Burst failure strength, thermal expansion coefficients, and thermal shock resistance of the extruded tubular LSGM, CGO, and YSZ electrolytes were investigated and compared. Three-point bending strength of these three extruded electrolyte materials were tested at room temperature, 600, 800, and 1000°C in air, and the results are discussed. © 2002 The Electrochemical Society. All rights reserved.

P-Type electronic conduction in CeO2- and LaGaO3-based solid electrolytes

Modifications of the e.m.f. and faradaic efficiency techniques, taking into account electrode polarization in the measuring cells, in combination with the use of electrodes having sufficiently high polarization resistances enable a precise determination of minor electronic contributions to the conductivity of solid electrolytes. These methods were used to determine the p-type conductivity of compositions based on La(Sr)Ga(Mg)O3-δ (LSGM) and Ce(Gd)O2-δ (CGO) at 900–1270 K. The oxygen ion transference numbers of these materials under oxygen/air gradient vary in the range 0.999–0.970, increasing with decreasing temperature. Substitution of 2 % gadolinium in Ce0.80Gd0.20O2-δ with praseodymium was found to increase the electron-hole conduction by 2.5 – 4 times. At temperatures above 700 K, both the partial oxygen ionic and p-type electronic conductivities of LaGaO3-based phases are higher than those in CGO. The electron-hole transport in LSGM tends to increase with the magnesium concentration, while the activation energy is essentially independent of composition. Electronic conduction in CGO and LSGM electrolytes was also found to be influenced by the ceramic microstructure.

Conversion of methane to syngas in a solid oxide fuel cell with Ni–SDC anode and LSGM electrolyte

A solid oxide fuel cell constructed from Ni–SDC anode and LSGM electrolyte was applied to the partial oxidation of methane to syngas (CO+H 2) at 700–800 °C with the merits of co-generation of electricity and controllable O 2 supply. It was found that the co-generated syngas at H 2/CO ratio of 1.4–2.0 varied with applied current densities, CH 4 flow rates and operating temperatures. The cell voltage at 100 mA cm −2 and 800 °C was 0.90 V, i.e. about 90 mW cm −2 power density could be obtained. The cell operating at 50 mA cm −2 for 24 h almost showed no degradation of the cell performance. The observed carbon deposition seemed mainly taking place by CH 4 cracking reaction.

Performance of intermediate temperature solid oxide fuel cells with La(Sr)Ga(Mg)O 3 electrolyte film

A La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) thin film was fabricated by the usual tape casting method using a doctor blade to reduce the operating temperature in solid oxide fuel cells (SOFCs). The resultant LSGM film was 130±3 μm in thickness and its relative density was over 99%. Also, the thin LSGM film showed a single phase, and its conductivity was 0.113 S/cm at 800 °C and 0.054 S/cm at 700 °C, respectively. Therefore, it seemed that the thin LSGM film was suitable as an electrolyte for intermediate temperature operating SOFCs. Ni–SDC and La(Sr)CoO 3 synthesized by spray pyrolysis were used as an anode and a cathode, respectively, and a single cell was fabricated with the thin LSGM film as an electrolyte. This single cell with the thin LSGM electrolyte exhibited excellent electrical performance, of which power density was over 0.7 W/cm 2 at 800 °C and 0.4 W/cm 2 at 700 °C. These results suggested that the LSGM-based SOFCs with the thin LSGM film in this study would exhibit adequate performance at a temperature lower than 700 °C.

Structure and Electrochemical Behavior of Plasma-Sprayed LSGM Electrolyte Films

ABSTRACTAn intermediate temperature solid oxide fuel cell (SOFC) electrolyte film of La0.8Sr 0.2Ga0.8Mg0.2O2.8 (LSGM) was fabricated using a plasma spray process. The microstructure and phase were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical behavior of the thermal sprayed LSGM film was investigated using electrochemical impedance spectroscopy (EIS). The study indicates that thermal spray can deposit a dense LSGM layer. It was found that the rapid cooling in the thermal process led to an amorphous or poor crystalline LSGM deposited layer. This amorphous structure has a significant effect on the performance of the cell. Crystallization of the deposited LSGM layer was observed during annealing between 500–600 °C. After annealing at 800 °C, the ionic conductivity of the sprayed LSGM layer can reach the same level as that of the sintered LSGM.

Interactions of LSGM electrolyte with different anode materials

Interactions of LSGM electrolyte with different anode materials

Increasing Power Density of LSGM-Based Solid Oxide Fuel Cells Using New Anode Materials

Chemical reactions between the superior perovskite oxide-ion conductor Sr- and Mg-doped (LSGM), and NiO have been studied by powder X-ray diffraction. The results showed that an extensive reactivity occurs as a result of La migration driven by a gradient of La chemical activity. La migration across the LSGM/electrode interfaces in a fuel cell leads to the formation of resistive phases at the interface, either or Use of 40 mol % -doped as an interlayer between anode and electrolyte as well as in the NiO-containing anode prevents all reactions found. Consequently, the air- cell maximum power density was increased to nearly 900 mW/cm2 at 800°C with a 600 μm thick LSGM electrolyte. No sign of degradation was observed at 800°C over 2 weeks for an interlayered cell under a loading current density of 250 mA/cm2. © 2001 The Electrochemical Society. All rights reserved.

Comparison of Mechamical and Thermal Properties of the Tubular LSGM, CGO, and YSZ Electrolytes

Comparison of Mechamical and Thermal Properties of the Tubular LSGM, CGO, and YSZ Electrolytes

Interface reactions in the NiO–SDC–LSGM system

The reactivity of NiO–SDC (samaria-doped ceria) anode material with a Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was studied by X-ray diffraction (XRD) and electrical measurements. It was found that a LaNiO 3-based compound in hexagonal structure formed in binary powder mixtures of NiO and LSGM after firing at 1150°C. Reaction between SDC and LSGM was also observed. Several SDC peaks merged with the adjacent LSGM peaks during firing, and a SrLaGa 3O 7 compound was identified as a reaction product. Reaction between LSGM and SDC could cause more than 50% loss in the ionic conductivity of LSGM–SDC electrolytes sintered at 1350°C. The measured conductivity of an LSGM electrolyte with a NiO–LSGM anode prepared at 1350°C was extremely low, indicating that the LaNiO 3-based new phase is highly insulating. The reaction between NiO and SDC was not so obvious in comparison with NiO–LSGM and SDC–LSGM binary mixtures.

Ni-SDC cermet anode for medium-temperature solid oxide fuel cell with lanthanum gallate electrolyte

The polarization properties and microstructure of Ni-SDC (samaria-doped ceria) cermet anodes prepared from spray pyrolysis (SP) composite powder, and element interface diffusion between the anode and a La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ (LSGM) electrolyte are investigated as a function of anode sintering temperature. The anode sintered at 1250°C displays minimum anode polarization (with anode ohmic loss), while the anode prepared at 1300°C has the best electrochemical overpotential, viz., 27 mV at 300 mA cm −2 operating at 800°C. The anode ohmic loss gradually increases with increase in the sintering temperature at levels below 1300°C, and sharply increases at 1350°C. Electron micrographs show a clear grain growth at sintering temperatures higher than 1300°C. The anode microstructure appears to be optimized at 1300°C, in which nickel particles form a network with well-connected SDC particles finely distributed over the surfaces of the nickel particles. The anode sintered at 1350°C has severe grain growth and an apparent interface diffusion of nickel from the anode to the electrolyte. The nickel interface diffusion is assumed to be the main reason for the increment in ohmic loss, and the resulting loss in anode performance. The findings suggest that sintering Ni-SDC composite powder near 1250°C is the best method to prepare the anode on a LSGM electrolyte.

Interfacial Reaction between Nickel Oxide and Lanthanum Gallate during Sintering and its Effect on Conductivity

The results of interdiffusion and reaction between NiO and strontium‐ and magnesium‐doped lanthanum gallate (LSGM) during sintering were investigated. Electron microprobe analysis showed that the NiO content of LSGM sintered 4 h at 1350°C was slightly >2 wt% within 5 µm of the interface, which is equivalent to 7 mol% nickel on B cation sites. This concentration decreased rapidly to <0.25% at a distance of 15 µm. The interfacial reaction between NiO and LSGM, however, led to the formation of a LaSrGa(Ni)O4‐delta‐type phase. A separate experiment involving conductivity measurements of nickel‐doped LSGM indicated that the oxygenion conductivity did not decrease significantly if the nickel content was <5%‐8%. At higher nickel contents, the conductivity increased in air because of hole conduction and markedly decreased under conditions of low oxygen pressure because of the formation of the LaSrGa(Ni)O4‐delta‐type phase. The nickel ions in the LSGM electrolyte and in the reaction product, LaSrGa(Ni)O4‐delta, were stable as Ni2+ at reduced oxygen pressures and, therefore, did not cause electronic shorting.

1358. Background gas pressure dependence and spatial variation of spontaneously generated magnetic fields in laser-produced plasmas: R S Case and F Schwirzke, J Appl Phys, 46 (4), 1975, 1493–1498

A novel perovskite oxide Ba0.9Co0.5Fe0.4Nb0.1O3−δ (BCFN) was prepared and characterized as oxygen electrode for solid oxide electrolysis cells (SOECs) using La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) as electrolyte. Symmetrical half-cell study shows that the polarization resistance of BCFN is only 0.08 Ω cm2 at 750 °C in air. Electrochemical impedance spectra and voltage-current curves of the electrolysis cell with the configuration of BCFN|LSGM|La0.4Ce0.6O2−x|Ni–Ce0.9Gd0.1O1.95 were measured as a function of operating temperature and steam concentrations to characterize the electrolysis cell performances. Under an applied electrolysis voltage of 1.5 V, the maximum consumed current density increased from 0.835 A cm−2 at 700 °C to 3.237 A cm−2 at 850 °C with 40 vol.% absolute humidity (AH), and the hydrogen generation rate of the cell can be up to 1352 mL cm−2 h−1 with 40 vol.% AH at 850 °C. Further, the electrolysis cell has showed very stable performance during a 200 h short-term electrolysis testing, indicating that BCFN can be a very promising candidate for the oxygen electrode of SOECs using LSGM electrolyte.

1355. Further studies of electron emission areas on electropolished copper surfaces in vacuum: G A Farrall et al, J Appl Phys, 46 (2), 1975, 610–617

A novel perovskite oxide Ba0.9Co0.5Fe0.4Nb0.1O3−δ (BCFN) was prepared and characterized as oxygen electrode for solid oxide electrolysis cells (SOECs) using La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) as electrolyte. Symmetrical half-cell study shows that the polarization resistance of BCFN is only 0.08 Ω cm2 at 750 °C in air. Electrochemical impedance spectra and voltage-current curves of the electrolysis cell with the configuration of BCFN|LSGM|La0.4Ce0.6O2−x|Ni–Ce0.9Gd0.1O1.95 were measured as a function of operating temperature and steam concentrations to characterize the electrolysis cell performances. Under an applied electrolysis voltage of 1.5 V, the maximum consumed current density increased from 0.835 A cm−2 at 700 °C to 3.237 A cm−2 at 850 °C with 40 vol.% absolute humidity (AH), and the hydrogen generation rate of the cell can be up to 1352 mL cm−2 h−1 with 40 vol.% AH at 850 °C. Further, the electrolysis cell has showed very stable performance during a 200 h short-term electrolysis testing, indicating that BCFN can be a very promising candidate for the oxygen electrode of SOECs using LSGM electrolyte.

1351. 1–17 keV positive-ion-induced electron ejection from tungsten, molybdenum and vanadium: N Cook and R B Burtt, J Phys D: Appl Phys, 8 (7), 1975, 800–811

A novel perovskite oxide Ba0.9Co0.5Fe0.4Nb0.1O3−δ (BCFN) was prepared and characterized as oxygen electrode for solid oxide electrolysis cells (SOECs) using La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) as electrolyte. Symmetrical half-cell study shows that the polarization resistance of BCFN is only 0.08 Ω cm2 at 750 °C in air. Electrochemical impedance spectra and voltage-current curves of the electrolysis cell with the configuration of BCFN|LSGM|La0.4Ce0.6O2−x|Ni–Ce0.9Gd0.1O1.95 were measured as a function of operating temperature and steam concentrations to characterize the electrolysis cell performances. Under an applied electrolysis voltage of 1.5 V, the maximum consumed current density increased from 0.835 A cm−2 at 700 °C to 3.237 A cm−2 at 850 °C with 40 vol.% absolute humidity (AH), and the hydrogen generation rate of the cell can be up to 1352 mL cm−2 h−1 with 40 vol.% AH at 850 °C. Further, the electrolysis cell has showed very stable performance during a 200 h short-term electrolysis testing, indicating that BCFN can be a very promising candidate for the oxygen electrode of SOECs using LSGM electrolyte.