LSGM Thin Film Research Articles

Grain Size Effect on Conductivity of LSGM Thin Film Electrolyte for Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) consisting of ion conductive ceramics has various advantages such as the high generating efficiency, the utilization of hydrocarbon-containing fuel and the non-necessity of expensive rare metal catalyst. Sr and Mg dopoed Lanthunum Gallate (La0.9Sr0.1Ga0.8Mg0.2O3-δ, LSGM) is a well-known electrolyte for solid oxide fuel cell because of the high conductivity.It is said that thin film material can exhibit different characterization from bulk material. In our former study, we tried to reveal the mechanism of the conductivity change of LSGM thin film from the bulk. The LSGM thin films with different thickness deposited on sapphire substrate by radio frequency magnetron sputtering was studied. The grains in the thicker film were larger than those in the thinner film. The thicker the film was, the conductivity increased and the activation energy decreased. We suggested this was caused by the smaller bulk resistivity than the grain boundary resistivity. It is necessary to develop the method to separate the resistivity into the bulk resistivity and the grain boundary resistivity to confirm this hypothesis.In this study, the radio frequency magnetron sputtering was used for obtaining LSGM films on LaSrGaO4 single crystal substrate. To crystallize and control the grain size in the LSGM film, we conducted post-annealing under various temperature. We evaluated the grain size in the LSGM film with a scanning electron microscope and measured the conductivity by electrochemical impedance spectroscopy. We try to separate the resistivity into the bulk resistivity and the grain boundary resistivity by using an equivalent circuit based on Brick-Layer model. In this paper, we report the grain size effect on the electrical conductivity in LSGM thin film.

Influence of Substrate on Conductivity of Sr and Mg Doped Lanthanum Gallate Thin Film Electrolyte for Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) consisting of ion conductive ceramics has various advantages such as the high generating efficiency, the utilization of hydrocarbon-containing fuel and the non-necessity of expensive rare metal catalyst. Yttria-stabilized Zirconia (YSZ) or Gadolinium-doped Ceria (GDC) are mainly used as the electrolyte for SOFC. Strontium- and Magnesium-doped Lanthanum Gallate (La0.9Sr0.1Ga0.8Mg0.2O3-δ, LSGM) has higher conductivity than YSZ, negligible electronic conduction and high chemical stability in a wide oxygen partial pressure range compared to GDC.Recently, it was reported that YSZ and GDC thin films have different values of ion conductivity from those of the bulk. LSGM should have the similar phenomenon. The reason for this change of the conductivity is assumed to be the lattice strain in the thin film, the difference between the bulk resistivity and the grain boundary resistivity or space charge layers at homo- or hetero-junctions. However, the mechanism of the conductivity change of LSGM thin film from the bulk is not revealed.In this study, the radio frequency magnetron sputtering, which is a reliable method for preparing thin film, was used for obtaining various thickness films on sapphire and quartz substrate. However, the deposited film was amorphous. To obtain the crystallized LSGM film, we investigated the influence of the annealing temperature. By proper post-annealing, crystallized LSGM film was obtained. We evaluated the crystallinity by X-ray diffraction, observed the microstructure with a scanning electron microscope and measured the conductivity by electrochemical impedance spectroscopy. In this paper, we report the effect on the electrical conductivity of the difference of thermal expansion co efficiency between LSGM thin film and the substrate.

Specific considerations for obtaining appropriate La1−xSrxGa1−yMgyO3−δ thin films using pulsed-laser deposition and its influence on the performance of solid-oxide fuel cells

To obtain La1−xSrxGa1−yMgyO3−δ (LSGM) thin films with the appropriate properties, pulsed-laser deposition (PLD) is employed, and specific considerations regarding control of the deposition parameters is investigated. It is demonstrated that with a target of stoichiometric composition, appropriate LSGM thin films cannot be produced because of the deviation of the composition from the target to the thin film. Only after adjusting the target composition an LSGM thin film with an appropriate composition and phase can be obtained. The optimized LSGM thin film possesses an electrical conductivity close to that of the bulk LSGM. In contrast, non-optimized thin films do not yield any measurable electrical conductivity. The impact of the optimization of the LSGM thin-film electrolyte on the cell performance is quite significant, in that a solid-oxide fuel cell (SOFC) with an optimized LSGM thin-film electrolyte produces a maximum power density of 1.1 W cm−2 at 600 °C, whereas an SOFC with a non-optimal LSGM thin-film electrolyte is not operable.

Electrochemical Characterization of La0.9Sr0.1Ga0.8Mg0.2O3-δ Thin Film Electrolyte Deposited by Radio Frequency Magnetron Sputtering

Sr and Mg dopoed Lanthunum Gallate (La0.9Sr0.1Ga0.8Mg0.2O3-δ, LSGM) is a well-known electrolyte for solid oxide fuel cell because of the high conductivity. Thin film material can exhibit different characterization from bulk material. Thus, electrochemical characterization of the LSGM thin film electrolyte was measured by impedance spectroscopy in intermediate temperature range under various oxygen partial pressures. In order to prepare the reliable LSGM film, radio frequency magnetron sputtering was used for depositing method. Safire single crystal disk was used as the substrate. As deposited, the film was amorphous. To obtain the crystallized LSGM film, we investigated the influence of the annealing temperature and the heating rate when annealing. By proper post-annealing, crystallized LSGM film was obtained.

Improved performance of ceria-based solid oxide fuel cell using doped LaGaO3 films deposited by pulsed laser deposition

A dense La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) film is fabricated using the pulsed laser deposition (PLD) technique on a Ce0.8Sm0.2O2−δ (SDC) electrolyte which is prepared using a co-pressing process on a NiO–SDC anode substrate. The LSGM/SDC bilayer electrolyte cell with Sm0.5Sr0.5CoO3−δ–Ce0.8Sm0.2O2−δ (SSC–SDC, 70:30 wt.%) cathode achieves significantly enhanced cell performance, yielding open circuit voltage (OCV) value of 0.89 V and maximum power density of 758 mW cm−2 at 700 °C. The electrical current leakage in the SDC single layer cell caused by the reduction of Ce4+ to Ce3+ in reducing environment has been eliminated by depositing the LSGM thin film as a blocking layer; besides, the reaction between NiO and LSGM can be prevented due to the dense SDC electrolyte layer. The influence of oxygen pressure and post-annealing temperature on the crystallinity, microstructure and surface roughness of the LSGM films are studied for obtaining a high quality film. Characterization analysis of the cell shows that the bilayer electrolyte deposited by the PLD technique have retained the chemical, mechanical and structural integrity of the cell.

Preparation and electric characterization of single phase La0.8Sr0.2Ga0.8Mg0.2O3 and La0.8Sr0.2Ga0.8Mg0.115Co0.085O3 thin films

La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) and La0.8Sr0.2Ga0.8Mg0.115Co0.085O3 (LSGMC) thin films were deposited on single crystalline (001) Al2O3 substrates using a pulsed laser deposition technique. The LSGM and LSGMC thin films exhibited only a single phase, which was verified through x-ray diffraction (XRD) experiments. Scanning electron microscopy (SEM) showed that the grain size of the LSGM film was smaller than that of the LSGMC films. Below 800 K, the ionic conductivity of both the thin films was higher than that of bulk sample. Furthermore, the LSGM thin film showed higher ionic conductivity than the LSGMC thin film at temperatures above 600 K.

The Growth Mechanism of LSGM Thin Film Electrolyte by RF Magnetron Sputtering

In order to discuss the growth mechanism of LSGM films, La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) thin films electrolytes were fabricated on Si substrates by RF magnetron sputtering. The atomic force microscope (AFM) and X-ray diffraction analyzer (XRD) were used to analyze film surface morphology and phase components. The results show that LSGM films are grown with island structure. When the deposition time increases to 30min, the preferred growth orientations appears, which is (112) crystal face. The longer deposition time is, and the rougher the surface possesses.

Preparation and characterization of La0.9Sr0.1Ga0.8Mg0.2O3−δ thin film electrolyte deposited by RF magnetron sputtering on the porous anode support for IT-SOFC

Thin films of solid electrolyte La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) were deposited by RF magnetron sputtering onto porous La0.7Sr0.3Cr0.5Mn0.5O3−δ (LSCM) anode substrates. The effects of substrate temperature, sputtering power density and sputtering Ar gas pressure on the LSGM thin film density, flatness and morphology were systematically investigated. RF sputtering power density of 7.8Wcm−2, substrate temperature of 300°C and sputtering Ar gas pressure of 5Pa are identified as the best technical parameters. In addition, a three-electrode half cell configuration was selected to investigate the electrochemical performance of the thin film. The LSGM film deposited at optimum conditions exhibited a lower area specific ohmic resistance of 0.68Ωcm−2 at 800°C, showing that the practicability of RF magnetron sputtering method to fabricate LSGM electrolyte thin film on porous LSCM anode substrates.

Intermediate Temperature Solid Oxide Fuel Cells Using LaGaO3 Based Perovskite Oxide for Electrolyte

Solid Oxide Fuel Cells (SOFCs) show a great promise as new power generators with high energy conversion efficiency. Decreasing operating temperature is critically requested for the further improvement in SOFC performance, in particular, for improving stability. Perovskite oxide of LaGaO3, doped with La and Mg exhibits the high oxide ion conductivity over wide PO2 range; the value is higher than that of Y2O3 stabilized ZrO2 by an order of magnitude at 773 K and useful for electrolyte of SOFC operating at intermediate temperature range. When LaGaO3-based oxide was used as the electrolyte of SOFC, the power density could be improved greatly, in particular in low temperature range. In this study, power generation property of SOFC using LaGaO3 electrolyte and also the improvement in power density of the cell by using a LaGaO3 thin film is also introduced. The maximum power density of the cell using LaGaO3 based oxide is as high as 0.6 W/cm2 at 773 K. This suggests that SOFC could be operable at temperature lower than 773 K. Tubular type cell stack using LSGM thin film is also introduced.

Fabrication and Characterization of the LSGM Thin Film Electrolyte by RF Magnetron Sputtering

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Synthesis and characterization of LSGM thin film electrolyte by RF magnetron sputtering for LT-SOFCS

La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) thin film electrolytes of 1.6–5 μm thicknesses were fabricated on Ni-based anode supports by RF magnetron sputtering using a sintered LSGM target and post annealing in air. The effect of sputtering gas pressure on the LSGM thin film density was examined. The effect of flatness of the Ni-based anode supports on the gas tightness and oxygen-ion conductivity was clarified. RF magnetron sputtering was conducted in a mixed gas of Ar and O 2. The Ni-based anode supports were heated to 400 °C during the deposition. The post annealing was carried out at 1100 °C in air. The microstructure of the fabricated LSGM thin films and compatibility between the fabricated LSGM thin film and the Ni-based anode support were examined using FE-SEM, EDX and XRD. The gas tightness of the fabricated LSGM thin film electrolytes was confirmed by measuring the open circuit voltage. The composition of the fabricated LSGM thin films was determined by ICP analysis. The fabricated thin film electrolytes, which were annealed at 1000-1100 °C, consisted of the LSGM single phase with the perovskite structure. There was no element migration between the LSGM thin film and the Ni-based anode support. The fabricated LSGM thin films were gas tight. The density of the LSGM thin film fabricated under the sputtering gas pressure of 1 Pa were higher than those sputtered at 2 Pa. The data clearly showed the feasibility of the RF magnetron sputtering method to directly fabricate the LSGM thin film electrolyte on the Ni-based anode.

Fabrication and Testing of a Doped Lanthanum Gallate Electrolyte Thin-Film Solid Oxide Fuel Cell

A supported lanthanum gallate (LSGM) electrolyte thin-film solid oxide fuel cell with Ni-YSZ cermet anode and strontium-doped lanthanum manganite (LSM)-yttria stabilized zirconia (YSZ) composite cathode was, for the first time, fabricated and tested. The cell was prepared by an unconventional approach, in which an LSGM thin film (about 15 μm thick) was first deposited on a porous substrate such as a porous YSZ disk by a wet process and sintered at a high temperature (above 1400°C). NiO was then incorporated into the porous substrate by a carefully controlled impregnation process and fired at a much lower temperature. In this way, the severe reaction between LSGM and NiO at a high temperature, which is required for the full densification of LSGM film, can be avoided. A strontium-doped (LSM)-YSZ composite cathode was screen printed on the surface of the LSGM film and then fired at 1250°C. The electrolyte resistances of the SOFC single cells fabricated by this approach are much lower compared to those of thick LSGM film supported cells. A maximum output power density of over at 800°C with as fuel and air as oxidant for a fabricated cell was achieved. © 2002 The Electrochemical Society. All rights reserved.