Thin Film Yttria-stabilized Zirconia Electrolyte Research Articles

Improved Reversibility of Thin-Film Solid Oxide Cells at 500 °C by Tailoring Sputtering Processes for Depositing Yttria-Stabilized Zirconia Electrolyte.

The present study investigates the impact of sputtering configurations on the microstructure and crystallinity of thin-film yttria-stabilized zirconia electrolytes for anodized aluminum oxide-supported all-sputtered thin-film reversible solid oxide cells. Employing various sputtering parameters, such as target-substrate distance and substrate rotation speed, the present study reveals distinct surface characteristics and crystalline structures of thin-film yttria-stabilized zirconia. The microstructure analysis includes scanning electron microscopy and atomic force microscopy examinations, uncovering the influence of the process parameters on the surface morphology, roughness, and grain size. X-ray diffraction data illustrate the texture preferences and crystallite characteristics. The electrochemical characterization of the reversible solid oxide cells demonstrates that the optimized sputtering configuration significantly outperforms the others in both SOFC and SOEC modes, showing exceptional current densities of 964 mA/cm2 at 1.3 V in electrolysis mode at 500 °C. Electrochemical impedance spectroscopy further reveals improved charge transfer reactions at the interface of the electrolyte. The enhanced electrochemical performance is attributed to the unique microstructure and crystallinity of the thin film of yttria-stabilized zirconia. The record-breaking electrolysis performance of this work at 500 °C underscores the potential of tailored sputtering parameters in optimizing the reversible solid oxide cell performance.

Nanocrystal Engineering of Thin-Film Yttria-Stabilized Zirconia Electrolytes for Low-Temperature Solid-Oxide Fuel Cells.

To overcome significantly sluggish oxygen-ion conduction in the electrolytes of low-temperature solid-oxide fuel cells (SOFCs), numerous researchers have devoted considerable effort to fabricating the electrolytes as thin as possible. However, thickness is not the only factor that affects the electrolyte performance; roughness, grain size, and internal film stress also play a role. In this study, yttria-stabilized zirconia (YSZ) was deposited via a reactive sputtering process to fabricate high-performance thin-film electrolytes. Various sputtering chamber pressures (5, 10, and 15 mTorr) were investigated to improve the electrolytes. As a result, high surface area, large grain size, and residual tensile stress were successfully obtained by increasing the sputtering pressure. To clarify the correlation between the microstructure and electrolyte performance, a YSZ thin-film electrolyte was applied to anodized aluminum oxide-supported SOFCs composed of conventional electrode materials which are Ni and Pt as the anode and the cathode, respectively. The thin-film SOFC with YSZ deposited at 15 mTorr exhibited the lowest ohmic resistance and, consequently, the highest maximum power density (493 mW/cm2) at 500 °C whose performance is more than five times higher than that of the cell with YSZ deposited at 5 mTorr (94.1 mW/cm2). Despite the basic electrode materials, exceptionally high performance at low operating temperature was achieved via controlling the single fabrication condition for the electrolyte.

Model Based Comparative Analysis of GDC and YSZ Based Solid Oxide Fuel Cells

Designing solid oxide fuel cell (SOFCs) stacks for transportation applications places new challenges on SOFC architecture and operation with respect to power density, dynamic response, and thermal management. Recent developments in SOFCs with either thin-film yttria stabilized zirconia (YSZ) electrolytes (thickness ≤ 5 μm) or highly conductive, gadolinia-doped ceria (GDC) electrolytes (thicknesses ≥10 μm) enable thigh-power-density stack operation at inlet temperatures well below 700ºC with the potential for using compliant seals and lower cost ferrous interconnect materials. Applications, such as hybridized aircraft engines, can use such SOFC stacks if they meet strict requirements with respect to specific power and thermal management. Highly conductive GDC-based electrolytes offer pathways to high power-density SOFCs at operating temperatures below 650ºC, but the rise in mixed ionic electronic conductivity (MIEC) above 650ºC reduces open circuit voltages and thus fuel cell efficiency [1,2]. This necessitates thermal management to maintain operating temperatures and mitigate thermo-mechanical stresses within an SOFC. Thin-film YSZ electrolytes offer lower power densities below 650ºC, but avoid the penalties associated with MIEC behavior at higher temperatures and therefore reduce the challenges associated with thermal management at high power densities. In this work, a model-based approach is used to compare SOFC stack operation with thin-film YSZ electrolytes and with GDC-based electrolytes for operation on hydrogen and reformate fuels at high-power densities relevant for transportation applications.To calibrate models to experimental cell performance, polarization curves of a commercially available YSZ-based cell operating between 600-750ºC and of a high-power-density GDC cell operating between 500-650ºC are used to fit electrochemical model parameters for both electrolytes. Modeling of the YSZ based cell can neglect electronic charge transfer through the membrane electrolyte, but GDC-cell modeling must account for the multiple charge carriers (ceria polarons and oxygen vacancies) in the electrolyte [3]. Electrochemical parameters for ionic conductivities and electrochemical reaction rate parameters for oxide cathodes and nickel-electrolyte-composite anodes are fit to the experimental polarization data over the broad range of operating temperatures. Global rate expressions to account for internal reforming on the active nickel surfaces of anode are adopted from literature [4,5]. The calibrated cell model for each cell type is adopted to a down-the-channel discretized cell simulation to predict heat loss and temperature gradients at high current densities.This presentation compares GDC- and YSZ-based SOFCs in high power-density applications from fundamental and practical perspectives. The open-circuit voltages for GDC-based cells drops with increasing temperature to about 0.85 V/cell at 650°C which is lower than the Nernst open-circuit voltage of YSZ-based cells (≥ 1.05 V/cell) at similar conditions. Both types of cells can sustain power densities around 1.0 W/cm2 with high excess cathode air ratios ≥ 5 to keep temperature gradients near 10°C/cm. These results show that GDC-based cells support higher power densities at lower cell flow inlet temperatures < 600°C, whereas thin-film YSZ cells provide superior performance at flow inlets that drive cell temperatures > 600°C. Higher stack power densities > 1.0 W/cm2 must be supported by stack designs that alleviate high thermal stresses and allow steeper gradients of temperature. A summary of stack design and operational strategies that meet the stringent requirements of high power-density operation will be presented in the light of the modeling resuls..

A review on the preparation of thin-film YSZ electrolyte of SOFCs by magnetron sputtering technology

Solid oxide fuel cells (SOFCs) have become one of the most attractive energy conversion devices due to their fuel flexibility, environmental friendliness and promising energy conversion efficiency. However, the high operating temperature (typically above 800 °C) of SOFCs poses some challenges concerning stability, sealing integrity and safety. Reducing the operating temperature of SOFCs to 600 °C or lower is currently an important research topic in the field. One effective strategy is to reduce the thickness of the electrolyte with high stability and high performance at lower temperatures. Among the thin-film preparation technologies, magnetron sputtering is gaining attention due to the advantages in scaling up and commercialization. Here we compare and analyze various electrolyte preparation methods and present a comprehensive review of the preparation of oxygen-ion-conducting electrolyte thin films by magnetron sputtering technology. The yttria-stabilized zirconia (YSZ) electrolyte and YSZ-based bilayer or multilayer electrolyte are employed as examples due to their high stability and high ionic conductivity. The effects of processing parameters on the microstructures and properties of the electrolyte thin films, the relevant interfaces and full SOFCs are reviewed and discussed. Finally, we present some perspectives and directions for developing high-performance SOFCs with thin-film electrolytes prepared by magnetron sputtering technology.

Porous Nickel Based Half-Cell Solid Oxide Fuel Cell and Thin-Film Yttria-Stabilized Zirconia Electrolyte

In this work, a porous nickel anode for thin-film solid oxide fuel cell prepared by the simple powder hot-pressing method is investigated. Powders of Ni and pore-forming agent (PFA) were thoroughly mixed in different ratios, pressed in a mold and further sintered. The polishing technique with Yttria-Stabilized Zirconia (YSZ) powder has been developed to decrease the surface roughness of Ni-based anode in order to deposit a crack-free electrolyte layer. The 3 μm YSZ thin-film electrolyte was deposited by the pulsed laser deposition technique on the surface of the anode. Morphological and elemental analyses of the samples were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. X-ray diffraction was used for phase analysis and structural characterization. The specific surface areas of the resulting anodes were calculated from their isotherms of N2 adsorption and desorption using the Sorbtometer and calculated by Brunauer Emmett-Teller (BET) method. As a result, the highest mechanical strength and specific surface area (15.42 m2g-1) possessed a sample with the content of PFA equal to 40%, while its ionic conductivity at 800 °C reached 6. 4∙10-2 S/cm.

Effect of Microstructure Control of Thin Film Yttria Stabilized Zirconia Electrolyte for Solid Oxide Fuel Cells by Adjusting Oblique Angle and Target Substrate Distance of Sputtering Process

In the present study, thin film yttria stabilized zirconia (YSZ) electrolyte was fabricated for solid oxide fuel cells via radio frequency (RF) magnetron sputtering with variation in oblique angle and target substrate distance (TSD). Growth tendencies were differentiated through adjusted oblique angle and TSD during sputtering, thereby microstructure of YSZ was changed. Electrochemical behavior of microstructure-controlled thin film YSZ was investigated by means of applying YSZ to anodic alumina oxide (AAO) based solid oxide fuel cells (SOFC). On nanoporous AAO substrates, Pt anode, YSZ electrolyte, and Pt cathode were deposited serially all through sputtering. For depositing thin film YSZ electrolyte, oblique angle and TSD were differentiated into four cases each, while thickness was set to be equal. YSZ thin films were evaluated using FESEM, AFM, FIB-SEM, XRD, and XPS. Electrochemical performance was investigated through i-V plot and EIS.

Post-annealing of thin-film yttria stabilized zirconia electrolytes for anode-supported low-temperature solid oxide fuel cells.

The effects of a post-annealing treatment on the performance of low-temperature solid oxide fuel cells (LT-SOFCs) were investigated. Nickel oxide-samarium doped ceria (NiO-SDC) anodes and yttria stabilized zirconia (YSZ) electrolytes were deposited on anodized aluminum oxide (AAO) membranes by RF sputtering and DC reactive sputtering, respectively. The half-cell of YSZ/NiO-SDC was then heat-treated at 600 degrees C for 10 h, and a porous platinum (Pt) cathode was deposited on the annealed YSZ/NiO-SDC structure by DC magnetron sputtering. Electrochemical impedance spectroscopy (EIS) analysis revealed a significant decrease in the ohmic resistance and a slight increase in the cathodic impedance. Such a result may be attributed to the increased grain size and enhanced crystallinity of the YSZ electrolyte after the heat treatment. The maximum power density observed for the heat-treated cell was 35 mW/cm2 at 450 degrees C, more than three times higher than the 10 mW/cm2 value obtained for the as-deposited cell.

Interaction of La0.58Sr0.40Co0.20Fe0.80O3−δ cathode with volatile Cr in a stack test – Scanning electron microscopy and transmission electron microscopy investigations

Anode-supported solid oxide fuel cells with special thin-film yttria-stabilized zirconia electrolytes made by sol–gel technology were operated in a short stack sequentially for about 1300 h at temperatures of 700 °C and subsequently for 1200 h at 600 °C, respectively. The stack was operated galvanostatically at a constant current density of 500 mA cm−2. After operation, the stack was dismantled and the cells were analyzed with respect to Cr interaction with the LSCF cathode. Chemical analysis revealed typical overall Cr amounts of several tenths μg cm−2 cathode area depending on the operation time. SEM cross sections showed less SrCrO4 formation at the typical sites for LSCF (top side of cathode) but there was evidence of chromate formation at the border between the cathode and barrier (electrolyte) layer. This location of foreign phase formation was unexpected. Additional TEM characterizations were therefore conducted. The TEM investigation verified the presence of Cr-containing crystals and revealed pore formation in the barrier layer. The formation of SrCrO4 at this borderline and pore formation were found for the first time after SOFC stack operation.

Characteristics of Thin Film Yttria-Stabilized Zirconia Electrolyte by Atomic Layer Deposition for Thin Film Solid Oxide Fuel Cells

not Available.

Thin film yttria-stabilized zirconia electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by chemical solution deposition

Abstract A 500 nm thick thin film YSZ (yttria-stabilized zirconia) electrolyte was successfully fabricated on a conventionally processed anode substrate by spin coating of chemical solution containing slow-sintering YSZ nanoparticles with the particle size of 20 nm and subsequent sintering at 1100 °C. Incorporation of YSZ nanoparticles was effective for suppressing the differential densification of ultrafine precursor powder by mitigating the prevailing bi-axial constraining stress of the rigid substrate with numerous local multi-axial stress fields around them. In particular, adding 5 vol% YSZ nanoparticles resulted in a dense and uniform thin film electrolyte with narrow grain size distribution, and fine residual pores in isolated state. The thin film YSZ electrolyte placed on a rigid anode substrate with the GDC (gadolinia-doped ceria) and LSC (La0.6Sr0.4CoO3−δ) layers deposited by PLD (pulsed laser deposition) processes revealed that it had fairly good gas tightness relevant to a SOFC (solid oxide fuel cell) electrolyte and maintained its structural integrity during fabrication and operation processes. In fact, the open circuit voltage was 1.07 V and maximum power density was 425 mW/cm2 at 600 °C, which demonstrates that the chemical solution route can be a viable means for reducing electrolyte thickness for low- to intermediate-temperature SOFCs.

Microstructural factors of electrodes affecting the performance of anode-supported thin film yttria-stabilized zirconia electrolyte (∼1 μm) solid oxide fuel cells

The effects of the microstructural factors of electrodes, such as the porosity and pore size of anode supports and the thickness of cathodes, on the performance of an anode-supported thin film solid oxide fuel cell (TF-SOFC) are investigated. The performance of the TF-SOFC with a 1 μm-thick yttria-stabilized zirconia (YSZ) electrolyte is significantly improved by employing anode supports with increased porosity and pore size. The maximum power density of the TF-SOFCs increases from 370 mW cm −2 to 624 mW cm −2 and then to over 900 mW cm −2 at 600 °C with increasing gas transport at the anode support. Thicker cathodes also improve cell performance by increasing the active reaction sites. The maximum power density of the cell increases from 624 mW cm −2 to over 830 mW cm −2 at 600 °C by changing the thickness of the lanthanum strontium cobaltite (LSC) cathode from 1 to 2–3 μm.

Preparation of thin film YSZ electrolyte by using electrostatic spray deposition

Yttria-stabilized zirconia (YSZ) thin film was successfully deposited onto Ni–YSZ anode disk by the electrostatic spray deposition (ESD) technique. To deposit a dense YSZ thin film onto porous Ni–YSZ substrate, the influence of process parameter variables were examined. The relationship between process parameters and morphologies of YSZ films coated by ESD was investigated by means of SEM photography and X-ray diffraction (XRD). The result showed that dense YSZ film of average 10–15 μm thickness was deposited on the porous Ni–YSZ substrate with temperature of 400 °C, the precursor solution concentration of 0.05 M, nozzle-to-substrate distance of 30 mm, applied electric field of 18 kV, and deposition time of 90 min.

La 0.4Ce 0.6O 1.8–La 0.8Sr 0.2MnO 3–8 mol% yttria-stabilized zirconia composite cathode for anode-supported solid oxide fuel cells

The composite cathodes of La 0.4Ce 0.6O 1.8 (LDC)–La 0.8Sr 0.2MnO 3 (LSM)–8 mol% yttria-stabilized zirconia (YSZ) with different LDC contents were investigated for anode-supported solid oxide fuel cells with thin film YSZ electrolyte. The oxygen temperature-programmed desorption profiles of the LDC–LSM–YSZ composites indicate that the addition of LDC increases surface oxygen vacancies. The cell performance was improved largely after the addition of LDC, and the best cell performance was achieved on the cells with the composite cathodes containing 10 wt% or 15 wt% LDC. The electrode polarization resistance was reduced significantly after the addition of LDC. At 800 °C and 650 °C, the polarization resistances of the cell with a 10 wt% LDC composite cathode are 70% and 40% of those of the cell with a LSM–YSZ composite cathode, respectively. The impedance spectra show that the processes associated with the dissociative adsorption of oxygen and diffusion of oxygen intermediates and/or oxygen ions on LSM surface and transfer of oxygen species at triple phase boundaries are accelerated after the addition of LDC.

Electrochemical Characterization of Thin Films for a Micro-Solid Oxide Fuel Cell

One of the first technological benchmarks towards the realization of a micro solid oxide fuel cell is the production of thin film structures with adequate electrochemical properties. This paper describes the deposition of thin film yttria-stabilized zirconia electrolytes and lithographically patterned platinum and gold electrodes. By using conventional, ultraviolet lithography, electrode patterns were produced with features sizes as fine as 15 μm, enabling a more direct investigation into the role of the triple phase boundary. Impedance spectroscopy measurements show three arcs, ascribed to the grain, grain boundary and electrode processes, and an offset on the real axis due to the leads. The high frequency arc, ascribed to the ohmic resistance of the YSZ electrolyte, exhibited an activation energy of 1.0 eV, while the intermediate frequency arc, attributed to blocking grain boundaries, exhibited an activation energy of 0.69 eV. The low frequency, non-ohmic arc was found to be highly dependent upon the electrode material and exhibited activation energies of 0.91 eV for gold electrodes and 0.77 eV for platinum electrodes. The electrode impedances for different sample geometries were similar when normalized to the triple phase boundary length.