Nanoscale Yttria-stabilized Zirconia Research Articles

Fabrication of yttria-stabilized zirconia/La2O3 composite coating by electrophoretic deposition to improve high-temperature oxidation resistance of stainless steel

Nanoscale yttria-stabilized zirconia (YSZ) and La2O3 were used to prepare a composite coating by electrophoretic deposition (EPD) and sintering to improve the high-temperature oxidation resistance of AISI430 stainless steel. SEM, XRD, and TEM were used to identify the microstructure of the YSZ/La2O3 composite coating and the oxide film formed at 900 °C. The effect of the EPD voltage on the coating thickness was studied. The microstructure properties and phase transition of the composite coatings during sintering were identified. The oxidation behavior of the composite coating at 900 °C was investigated by analyzing the oxidation kinetics curve, oxidation spallation, the formation of the interfacial oxide film, and the evolution of the coating microstructure. A model of the microstructure evolution of the YSZ/La2O3 composite coating during EPD, sintering, and high-temperature oxidation was proposed and discussed.

Reversible Martensitic Phase Transition in Yttrium-Stabilized ZrO2 Nanopowders by Adsorption of Water

The present study was aimed at revealing the influence of the mechanical stress induced by water molecule adsorption on the composition of crystalline phases in the ZrO2 + 3 mol% Y2O3-nanoparticles. Three basic methods were used to determine the phase transition: neutron diffraction, Raman microspectroscopic scanning, and X-ray diffraction. The fact of reversible phase-structural β → α transformation and the simultaneous presence of two polymorphic structural modifications (β is the phase of the tetragonal syngony and α of monoclinic syngony in nanosized particles (9 nm)) under normal physical conditions was established by these methods. An assumption was made regarding the connection of the physical mechanism of transformation of the extremely nonequilibrium surface of nanoparticles with electronic exchange of the material of the near-surface layer of nanoparticles with the adsorption layer through donor–acceptor interaction. The principal possibility of creating direct-acting hydroelectric converters based on nanoscale YSZ (Yttria-Stabilized Zirconia) systems due to the reversible character of the considered effect was shown.

Effect of Initial ZrOCl₂ Concentration on the Homogeneous Precipitation of Nanoscale 3Y-TZP Powder.

Nanoscale yttria-stabilized zirconia (Y-TZP) powder was synthesized by homogeneous precipitation via urea hydrolysis, and the influence of a dispersing agent and the initial ZrOCl2 concentration on the powder characteristics was investigated. A precipitated gel was obtained from the reaction of the precursor solution with zirconium oxychloride, yttrium chloride, and urea with heating at 110 °C for 5 h. The initial ZrOCl2 concentration was controlled from 0.25 to 1 M. To observe the effect of adding a dispersing agent on the agglomeration of primary particles, we used two starting compositions, one with and the other without a dispersing agent, ammonium polymethacrylate. Two crystalline powders were obtained after drying, calcination, and milling the gel, and we investigated the powder characteristics, such as particle agglomeration, the specific surface area, the microstructure, and phase composition. Two scales of agglomerates were observed in the particle size distribution, namely, 190 to 362 nm at the primary scale and 1.6-4.0 μm at the secondary scale. The amount of secondary agglomerate increased from 6 to 20 vol% with the increasing initial ZrOCl2 concentration. The size of both types of agglomerate and the amount of secondary agglomerates decreased due to the addition of the dispersing agent, especially the primary agglomerate size. The sintered density and microstructure of Y-TZP were affected by the agglomeration behavior, especially the amount of secondary agglomerates.

Ag surface-coated with nano-YSZ as an alternative to Pt catalyst for low-temperature solid oxide fuel cells

Herein we propose silver surface-coated with nano-scale yttria-stabilized zirconia (YSZ) as a high-performance cathode for use in low-temperature solid oxide fuel cells (LT-SOFCs). YSZ was coated on the Ag cathode surface by sputtering of Y/Zr alloy films followed by thermal annealing for oxidation of YSZ. An electrolyte-support type SOFC was fabricated on 350-μm-thick gadolinium-doped ceria (GDC) pellets. The yttrium concentration and sputtering time for obtaining the YSZ coating layer was varied to optimize the cathode composition. It was determined that the GDC SOFCs with optimized Ag-YSZ cathodes significantly outperform cells with bare silver or platinum cathodes, which are considered to be the best-performing catalysts at low temperatures. The peak power density obtained using cells with Ag-YSZ cathodes was as high as ∼100 mW/cm2 at 450 °C, 3–4 times greater than the performance of cells with Ag or Pt cathodes. Electrochemical impedance spectroscopy was performed during fuel cell testing to compare polarization and charge transport performances of the Ag-YSZ cathodes. The long-term stability of the Ag-YSZ cathode was evaluated by monitoring the change in cathode morphology compared to the bare Ag and Pt cathodes.

Fabrication of nanoscale yttria stabilized zirconia for solid oxide fuel cell

Yttria stabilized zirconia (YSZ) is the most widespread electrolyte material for solid oxide fuel cell (SOFC) due to its high ionic conductivity and electronic resistivity over a wide range of oxygen partial pressures. In addition, it is chemically stable at high temperature in oxidizing and reducing atmospheres and chemically and mechanically compatible with the other cell components and gas tight. The objective of this paper is to review current status and related researches about the development of nanoscale YSZ used as electrolyte in SOFC from the viewpoint of materials nanostructure and performance associated with the fabrication and optimization processes. The latest development and achievement in nanoscale YSZ materials are presented. Challenges and research trends based on the fundamental understanding of the materials science and engineering for the nanoscale YSZ development for the commercially viable SOFC technologies are discussed.

Ionic properties of ultrathin yttria-stabilized zirconia thin films fabricated by atomic layer deposition with water, oxygen, and ozone

We compared the ionic properties of yttria-stabilized zirconia (YSZ) thin films prepared by atomic layer deposition (ALD) using various oxidants including water, oxygen, and ozone. Cross-plane conductivity measurements were performed at low temperature (50°C) and high temperature (450°C) using AC impedance spectroscopy. As a result, we have confirmed that the conductivity of ALD YSZ films below 300°C is greater by several orders of magnitude compared to the nano-scale YSZ thin films synthesized by other conventional techniques. Among the ALD YSZ samples, ALD YSZ fabricated using water showed the highest conductivity while ALD YSZ fabricated using ozone showed the lowest. We have analyzed this result in relation with grain morphology characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), and the chemical binding states measured by X-ray photoelectron spectroscopy (XPS).

ChemInform Abstract: On the Variability of Reported Ionic Conductivity in Nanoscale YSZ Thin Films

AbstractReview: 58 refs.

On the variability of reported ionic conductivity in nanoscale YSZ thin films

Yttria-stabilized zirconia (YSZ) is the most common material used as a solid oxide electrolyte, which is a key component in solid oxide fuel cells, solid oxide electrolysis cells, and certain chemical sensors. High efficiency in these devices requires increased oxygen ion conductance at intermediate temperatures. Nanoscale YSZ thin films are quite promising in this regard, as the conduction path may be reduced below what is conventionally achievable. Still, as the thickness is decreased to nanoscale, structural properties like lattice parameter and grain morphology are typically altered. These may affect the electrochemical properties in non-trivial ways. Recent reports on nanoscale YSZ thin films have provided inconsistent and, at times, controversial results. In this paper, we present a review of reports on nanoscale YSZ thin films, focusing principally on single component YSZ films as opposed to heterogeneous multilayer films. Reports of significantly increased conductivity come from studies that use a variety of substrates, grain morphologies, and, to some extent, film thicknesses. Mechanical strain in the films is not typically reported but is a suspected cause of the variability in conductivity.

Ion conduction in nanoscale yttria-stabilized zirconia fabricated by atomic layer deposition with various doping rates

The ion conduction of yttria-stabilized zirconia (YSZ) was studied by varying the doping ratios during atomic layer deposition (ALD). The ALD cycle ratio for the yttria and zirconia depositions was varied from 1:1 to 1:6, which corresponded to the doping ratios from 28.8% to 4.3%. The in-plane conductivity of ALD YSZ was enhanced by up to 2 orders of magnitude; the optimal ALD doping ratio (10.4%) was found to differ from that of bulk YSZ (8%). This different relationship between the doping ratio and the ion conduction for ALD YSZ versus bulk YSZ is due to the inhomogeneous doping in the vertical direction of the ALD YSZ films, as opposed to the homogenous doping of bulk YSZ.

Ion Conduction in Nanoscale Yttria-Stabilized Zirconia Thin Films Fabricated by Atomic Layer Deposition

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Incorporation of Hydroxyl Ions and Protons in Oxide Ion Vacancies in Nanoscale Yttria Stabilized Zirconia during Atomic Layer Deposition

This work provides direct evidence that protons are incorporated in yttria stabilized zirconia (YSZ) deposited by atomic layer deposition (ALD) during the fabrication of films and not from ambient water after deposition. An oxidant made of proton isotopes or deutrium was used as a tracer of the incorporated protons during the synthesis, and time-of-flight secondary mass ion mass spectrometry (TOF-SIMS) was conducted for depth profiling. We identified that protons or deutrium ions introduced during deposition truly favored to reside in the ALD YSZ layers and that the concentration of protons incorporated during ALD was related to the concentration of yttrium.

Incorporation of Hydroxyl Ions and Protons in Oxide Ion Vacancies in Nanoscale Yttria Stabilized Zirconia during Atomic Layer Deposition

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Scalable nanostructured membranes for solid-oxide fuel cells

The use of oxide fuel cells and other solid-state ionic devices in energy applications is limited by their requirement for elevated operating temperatures, typically above 800°C (ref. 1). Thin-film membranes allow low-temperature operation by reducing the ohmic resistance of the electrolytes. However, although proof-of-concept thin-film devices have been demonstrated, scaling up remains a significant challenge because large-area membranes less than ~ 100 nm thick are susceptible to mechanical failure. Here, we report that nanoscale yttria-stabilized zirconia membranes with lateral dimensions on the scale of millimetres or centimetres can be made thermomechanically stable by depositing metallic grids on them to function as mechanical supports. We combine such a membrane with a nanostructured dense oxide cathode to make a thin-film solid-oxide fuel cell that can achieve a power density of 155 mW cm⁻² at 510 °C. We also report a total power output of more than 20 mW from a single fuel-cell chip. Our large-area membranes could also be relevant to electrochemical energy applications such as gas separation, hydrogen production and permeation membranes.