Gadolinia-doped Ceria Thin Films Research Articles

Structure and ionic conductivity of nanoscale gadolinia-doped ceria thin films

Nanoscale 20 mol% gadolinia-doped ceria (GDC) thin films were prepared by RF sputtering on single crystal (0001) Al2O3 substrates. The films were polycrystalline with columnar grains that were very highly textured along the (111) direction. A moderate amount of lattice strain was observed when the thickness was less than 81 nm, similar to the grain size. Impedance spectroscopy measurements between 300 °C and 650 °C demonstrated that GDC thin films achieved highest conductivity at 81 nm thickness. The activation energy was ≈ 0.75 eV when thickness was under 81 nm but increased as the thickness increased above 81 nm. Constant conductivity values for all samples as the oxygen partial pressure varied between 10− 3 atm and 1 atm demonstrated that the conductivity was predominantly ionic.

Gadolinia Doped Ceria Thin Films Prepared by Aerosol Assisted Chemical Vapor Deposition and Applications in Intermediate‐Temperature Solid Oxide Fuel Cells

AbstractFurthermore, deposition at such low temperatures is promising for processing of thin film assemblies.The preparation of bi‐layer electrolytes of yttria stabilized zirconia and gadolinia doped ceria thin films by aerosol assisted chemical vapor deposition is demonstrated. Gadolinia doped ceria films as thin as 150 nm are applied as barrier layers between yttria stabilized zirconia electrolyte and La0.6Sr0.4CoO3–δ cathode in anode supported solid oxide fuel cells. High power densities above 850 mW cm–2 at 650 °C are only obtained with these barrier layers, indicating that the GDC thin films effectively inhibit the formation of unwanted interface reactions.

Epitaxial pore-free gadolinia-doped ceria thin films on yttria-stabilized zirconia by RF magnetron sputtering

Abstract A thin film of gadolinia-doped ceria (GDC) grown on (001) single crystal of yttria-stabilized zirconia (YSZ) was produced by RF magnetron sputtering using a stoichiometric target. Films deposited at room temperature showed columnar porosity which changed to equiaxed on annealing at 1150 °C. It is shown that films deposited at 500 °C were epitaxial, uniform in thickness, pore-free and remained dense after annealing at 1150 °C. This method can be used to attain reproducible control over important characteristics of the film such as structure, composition, orientation, thickness and morphology.

Fabrication of low-temperature solid oxide fuel cells with a nanothin protective layer by atomic layer deposition

Anode aluminum oxide-supported thin-film fuel cells having a sub-500-nm-thick bilayered electrolyte comprising a gadolinium-doped ceria (GDC) layer and an yttria-stabilized zirconia (YSZ) layer were fabricated and electrochemically characterized in order to investigate the effect of the YSZ protective layer. The highly dense and thin YSZ layer acted as a blockage against electron and oxygen permeation between the anode and GDC electrolyte. Dense GDC and YSZ thin films were fabricated using radio frequency sputtering and atomic layer deposition techniques, respectively. The resulting bilayered thin-film fuel cell generated a significantly higher open circuit voltage of approximately 1.07 V compared with a thin-film fuel cell with a single-layered GDC electrolyte (approximately 0.3 V).

Epitaxial and Polycrystalline Gadolinia-Doped Ceria Cathode Interlayers for Low Temperature Solid Oxide Fuel Cells

This paper presents the catalytic role of the gadolinia-doped ceria (GDC) and its surface grain boundaries in enhancing the oxygen incorporation kinetics of low-temperature solid oxide fuel cells (LT-SOFC). Epitaxial and polycrystalline GDC thin films were grown by pulsed laser deposition (PLD) on the cathode side of 300 μm-thick single crystalline (100) and 100 μm-thick polycrystalline YSZ substrates, respectively. Fuel cell current-voltage behavior and electrochemical impedance spectroscopy measurements were carried out in the temperature range of 350°C–450°C on both types of cells. Results of dc and ac measurements confirm that cathodic resistances of cells with epitaxial GDC layer are lower than that for the YSZ-only control cell. This is attributed to the higher surface exchange coefficient for GDC than YSZ. Moreover, the role of grain boundary density at the cathode side external surface was investigated on surface-engineered electrode-membrane assemblies (MEA) having different GDC surface grain sizes. MEAs having smaller surface grain size show better cell performance and correspondingly lower electrode interfacial resistance. Electrochemical measurements suggest that GDC grain boundaries at the cathode side contribute to enhance oxygen surface kinetics. These results provide an opportunity and a microstructure design pathway to improve performance of LT-SOFCs by surface engineering with nano-granular, catalytically superior thin GDC cathodic interlayers.

A simple, rapid spray method for preparing anode-supported solid oxide fuel cells with GDC electrolyte thin films

Abstract A simple, rapid and cost-effective technique, spray dry co-pressing process, was developed to prepare dense electrolyte thin films on porous anode substrates. Gadolinium doped ceria (GDC) electrolyte thin film with the thickness of 4 μm was prepared successfully on porous NiO–GDC anode substrate by the spray dry co-pressing process. The GDC electrolyte thin film was dense and uniform, and was well bonded to the porous NiO–GDC anode substrate. An anode-supported solid oxide fuel cell (SOFC) with 4 μm GDC electrolyte thin film was fabricated and its performance was evaluated at 400–600 °C with humidified hydrogen (3 vol.% H 2 O) as the fuel. The single cell showed an open circuit voltage (OCV) of 0.91 V and maximum power density of 771 mW cm −2 at 600 °C. The results demonstrate that the dense GDC thin films prepared by the spray dry co-pressing process are suitable for low-temperature anode-supported SOFC applications.

Anode-Supported SOFCs with Electrolyte Thin Films Prepared by Spray Coating

Dense gadolinium doped ceria (GDC) electrolyte thin films were prepared on porous NiO-GDC substrates by spray coating process. Microstructure of the GDC thin films and effect of preparation process on the microstructure were examined. SEM results show that uniform and dense GDC thin films with a thickness of approximately 1 μm were successfully prepared on porous NiO-GDC anodes. Anode-supported single cell with the thin GDC electrolyte film was tested using humidified hydrogen as a fuel, and exhibited relatively high electrical performance at low operating temperature (the maximum power density of 135 mW/cm2 at 600 °C). This means that the thin GDC film may be applicable to an electrolyte for anode-supported SOFCs. The experimental results suggest that the spray coating method developed in this study may offer a useful route for preparing thin and dense electrolytes of SOFCs.

Characteristics of Sputter-deposited Gadolinia-doped Ceria Thin Films on Al2O3/SiO2/Si Systems

Metal oxide films prepared by thin film technology have been reported for the potential applications on thin solid electrolyte layers for solid oxide fuel cells(SOFCs). Gadolinia-doped ceria(GDC) thin films and Al2O3 layers on SiO2/Si substrates are successively deposited by RF reactive magnetron sputtering from a cerium-gadolinium (90:10 at.%) alloy target and Al target in O2/Ar gas mixture and then perform post-thermal treatments at 300–700 ℃ and 900 ℃ for 2 h, respectively. Materials characteristics and chemical compositions of GDC films and Al2O3 layers are investigated by X-ray photoelectron spectroscopy(XPS), cross-sectional scanning electron microscopy(SEM), X-ray diffraction(XRD), and atomic force microscopy(AFM). Stoichiometric Al2O3 layers with polycrystalline structures are firstly prepared onto SiO2/Si substrates. A cubic fluorite structure with columnar crystallites of GDC films is successfully deposited on Al2O3/SiO2/Si systems. The chemical composition of 700 ℃-annealed GDC films is (Ce0.91Gd0.09)O1.94 and possesses a higher film density of 7.257 g/cm3. As a result, GDC thin films prepared by RF reactive magnetron sputtering and post-thermal treatments can be used as thin solid electrolyte layers for intermediate temperature SOFCs system as compared to the well-known yttria-stabilized zirconia(YSZ).

Oxygen surface exchange studies in thin film Gd-doped ceria

Electrical conductivity relaxation measurements were performed on gadolinium doped ceria thin films to evaluate chemical surface exchange rate of oxygen (Kex, cm/s) under reducing ambient. The measurements were performed under identical conditions in bulk and thin films as a function of thickness (35–440nm), temperature (943–1158K), and oxygen partial pressure (10−21–10−12atm) using a custom built small volume cell assembly. The Kex in thin films is found to be over an order lower than for bulk samples. Segregation effects in thin films likely lead to near-surface carrier depletion thereby decreasing oxygen exchange rate.

Gadolinium doped ceria thin films deposited by e-beam technique

E-beam deposition technique was used for formation of gadolinium doped ceria oxide (GDC) thin films. GDC thin films were grown by evaporating (Ce 0.9Gd 0.1)O 1.95 ceramic nanopowder. Operating technical parameters that influence thin film microstructure and crystallite size were studied. The GDC thin films were deposited on porous NiO–YSZ (nickel oxide–yttrium stabilized zirconium), optical quartz and Alloy 600 (Fe–Ni–Cr). The influence of substrate temperature on thin film (2–3 μm of thickness) structure and surface morphology was investigated by X-ray diffraction and scanning electron microscopy. It was found that substrate temperature (changed in the range of 20–500 °C) had the influence on the crystallite size and texture. Crystallite size grows up to 53–56 nm with increasing substrate temperature during the deposition. The GDC thin film growing texture is changing at higher than 300 °C substrate temperature when is chosen Alloy 600 substrate.

Growth and characterization of highly oriented gadolinia-doped ceria (111) thin films on zirconia (111)/sapphire (0001) substrates

Highly-oriented pure and gadolinia-doped ceria thin films have been grown on pure and zirconia (ZrO 2) (111)-buffered sapphire (Al 2O 3) (0001) substrates using oxygen plasma-assisted molecular beam epitaxy to understand the oxygen ionic transport processes in ceria based oxide thin films. Gadolinia-doped ceria films grown on sapphire substrate show polycrystalline features due to structural deformations resulting from the large lattice mismatch between the Al 2O 3 (0001) substrate and the ceria films. In contrast, the films, grown on a thin layer of ZrO 2 (111) buffered sapphire substrate, appear to be highly oriented in nature with predominant double domain (111) orientation. Oxygen ionic conductivity of these gadolinia-doped ceria films was measured as a function of gadolinium concentration and found to be efficient at relatively lower temperature operation compared to that of bulk polycrystalline, single crystalline yttria stabilized zirconia and gadolinia-doped polycrystalline ceria. Relative improvement in ionic conductivity of highly oriented gadolinia-doped ceria films (in the lower temperature regime) can be ascribed to the increased oxygen vacancies due to presence of Gd as well as high quality of the oriented thin films.

Thermal properties of 15-mol% gadolinia doped ceria thin films prepared by pulsed laser ablation

Thermal properties of 15-mol% gadolinia doped ceria thin films (Ce0.85Gd0.15 O1.925) prepared by pulsed laser ablation on silicon substrates in the temperature range 473–973 K are presented. Thermal diffusivities and thermal conductivities were evaluated using photoacoustic spectroscopy. The influence of grain size on thermal properties of the films as a function of deposition temperature is studied. It is observed that the thermal diffusivity and the conductivity of these films decreases up to 873 K and then increases with substrate temperatures. The thermal properties obtained in these films are discussed on the basis of influence of grain size on phonon scattering.

Microstructural and Electrical Properties of Gadolinium Doped Ceria Thin Films Prepared by Atomic Layer Deposition (ALD)

In spite of its undesirable electronic conductivity under reducing atmosphere, a gadolinium doped ceria (COO) remains one of the most promising candidates for replacing yttria-stabilised zirconia as electrolyte for SOFC, operating at lower temperature. For the first time, atomic layer deposition (AID), a well-suited method for binary compounds and their doping, was used for the fabrication of SOFC components. CGO thin layers less than 1 μm-thick were achieved by this technique. SEM analysis, EDS measurements, and XRD have been carried out in order to determine the microstructural characteristics of the ALD layers. Dense, uniform, and well-covereing layers have been deposited onto several kinds of substrates, in particular, on porous SOFC electrodes. Furthermore, the electrical properties of CGO thin films were investigated by means of impedance spectroscopy. In particular, the ionic conductivity of the deposited material was determined and compared with the litterature data.

Single-crystal and Nano-columnar Growth of Gadolinium-doped Ceria Thin Films on Oxide Substrates Studied Using Electron Microscopy

ABSTRACTGadolinium-doped ceria (GDC) thin films were grown by pulsed laser ablation on various oxide single crystal substrates including MgO, YSZ, LAO, NGO, and STO with different film-substrate lattice mismatch ratios. The film microstructures were characterized mainly by using electron microscopy. A clear influence of the filmsubstrate lattice mismatch on the film crystallinity has been observed. The GDC films usually exhibit columnar grain growth for a large range of film-substrate lattice mismatch ratios. A cube-on-cube growth of GDC film on MgO has been observed with a surprisingly high lattice mismatch ratio of 28%. The highest film crystallinity is obtained on the LAO substrates under a small compressive strain. This single-crystalline GDC film shows no columnar grain growth but presents a novel directionally-aligned precipitated Gd-rich nanoparticle system, which plays a specific role in relaxing various kinds of strain fields induced during the thin film growth to ensure the film crystallinity.