Μm Thick Yttria-stabilized Zirconia Research Articles

Carbon nanotube sheet as a current collector for low-temperature solid oxide fuel cells

The utilization of Carbon Nanotube (CNT) sheets as current collectors for Solid Oxide Fuel Cells (SOFCs) was investigated in this study. A direct spinning method was employed for the synthesis of the 15 μm thick CNT sheet, which demonstrated high efficiency and cost-effectiveness. The material properties of the CNT sheet were characterized as a cathodic current collector and were subsequently integrated into 500 μm thick yttria-stabilized zirconia pellet-based SOFCs. The electrochemical performance of the SOFCs was evaluated at a temperature of 500 °C, resulting in a significant increase of 34.7% compared to the traditional SOFCs employing Pt mesh current collectors. Electrochemical Impedance Spectroscopy (EIS) analysis was performed to demonstrate that the observed performance enhancement was attributed to a reduction in both ohmic and charge transfer resistance. This highlights the potential of CNT sheet current collectors in not only decreasing ohmic resistance but also facilitating the reaction kinetics in solid oxide cells.

Thermal Cyclic Behaviour of Conventional YSZ and Mullite-YSZ Thermal Barrier Coatings

Nowadays commonly used thermal barrier coatings (TBC) are based on yttria stabilized zirconia (YSZ). Addition of mullite phase into the YSZ coating can improve resulting high temperature properties. The contribution focuses on high temperature cyclic oxidation behaviour of two TBC systems with different top coats (TC) deposited by the means of atmospheric plasma spraying. The initial mullite-YSZ powder mixture consisted of 29 vol. % of mullite and 71 vol. % of YSZ. The conventional TBC system consisted of ~ 150 µm thick NiCoCrAlYHfSi bond coat (BC) and ~ 300 µm thick YSZ top coat. The experimental mullite-YSZ (MYSZ) TBC system consisted of ~ 150 µm thick NiCoCrAlYHfSi bond coat, ~ 100 µm thick YSZ interlayer and ~ 200 µm thick mullite-YSZ top coat. The experimental TBC proved higher lifetime, durability and phase stability and also lower grow rate of thermally grown oxide (TGO) compared to conventional TBC. Lifetime, phase stability and changes in the microstructure of TBCs after the furnace cyclic oxidation test were evaluated by the means of scanning electron microscopy equipped with EDX analyzer and X-ray diffraction techniques. Oxidation kinetics of TGO was calculated based on thickness determined utilizing digital image analysis.

Evaluation of corrosion resistance of Gd2O3/YSZ thermal barrier coating using electrochemical impedance spectroscopy

Inconel 718 samples were plasma sprayed with 300 µm thick pure Yttria stabilized zirconia (YSZ) over the 100 µm bond coat. Next the gadolinium oxide is doped in percentages of 8, 12, 25 with the YSZ and coated on the 100 µm bond coat. In multilayer coatings the specimens of Inconel 718 are coated with 100 µm thick bond coat over which 100 µm thick YSZ ceramic coat is applied. Above the YSZ coatings the percentages of 8, 12, 25 gadolinium oxide is doped with the YSZ respectively to form another 100 µm ceramic coat. Again the 100 µm YSZ ceramic topcoat is applied over the doped layer. As deposited coated samples were corrosion tested to study the corrosion behaviour in the corrosion environment. The increased value of Rct and decreased value of the Cdl relates that the corrosion resistance of YSZ coated samples which is relatively compared to Gd2O3 doped YSZ top coated samples.

Fabrication and Characterization of YSZ/GDC Bilayer Electrolyte Thin Films by Spray-Coating and Co-Sintering

Yttria-stabilized zirconia (YSZ) is the most popular electrolyte material for solid oxide fuel cells (SOFCs). However, when cobaltite-based perovskite cathode materials, for example lanthanum strontium cobalt ferrite (LSCF), are used, an insulating layer is easy to be formed at the cathode-electrolyte interface. For preventing the interfacial reaction, a gadolinium-doped ceria (GDC) interlayer is usually employed between YSZ and cathode. In this work, we investigated the fabrication of YSZ/GDC bilayer electrolyte thin films by a simple spray coating process and co-sintering. Dense YSZ/GDC bilayer electrolyte thin films were successfully fabricated. There is no crack and delamination observed for the YSZ/GDC bilayer. A Ni-YSZ/YSZ/GDC/LSCF-GDC anode-supported single cell with 4 µm thick YSZ layer and 2 µm thick GDC layer shows an open-circuit voltage of 1.1 V and a maximum power density of about 0.6 W/cm2 with humidified H2 as fuel and air as oxidant at 700°C.

Protection offered by thermal barrier coatings to Al-Si alloys at high temperatures – A microstructural investigation

Abstract Thermal barrier coatings, with ∼50 µm thick Nickel-Aluminide bond coat and ∼250 µm thick Yttria-Stabilized zirconia ceramic top coats were synthesized by Air Plasma Spray coating process on flat plates machined from Al-11Si alloy diesel engine pistons. Coating process parameters and qualifications that were followed were based on previous studies made on the same substrates. The ceramic coatings were subjected to various thermal treatments such as (a) thermal shock cycling tests and (b) continuous heating in a furnace. Uncoated Al-Si samples were simultaneously subjected to the same thermal treatments and used as reference to study the protection offered by the coatings to the base metal substrates. Thermal shock cycles tests involved subjecting the coated and uncoated Al-Si plates to oxy-acetylene flame to allow the ceramic surface to be maintained at 500 °C for 1000 cycles (one cycle comprised of heating for 60 s, withdrawal from flame and forced cooling in ambient air for 60 s) and similar thermal shock cycles in an electric furnace. The specimen were also heated in a furnace at 300 °C for 1000 continuous hours. Stresses induced during thermal shock cycles and oxidation of bond coat-ceramic coat interface during the exposure to heat are the main reasons for the coating’s failure. Details of an investigation on the microstructural changes and oxidation behaviour of the substrate and the ability of the coatings to protect the metal substrates from oxidation are presented. Microstructural studies were carried out by employing a Scanning Electron Microscope attached with Energy Dispersive X-ray spectroscopy facility. The findings were compared on (a) uncoated Al-Si alloy and (b) thermal barrier coated Al-Si alloy with a goal to understand the capability of the coatings to protect the metal from the influences of thermal treatments, at temperatures lower than the melting point of the Al-Si alloy.

Protective Ceramic Coatings for Solid Oxide Fuel Cell (SOFC) Balance-of-Plant Components

Solid oxide fuel cells (SOFCs) have the potential to meet the growing need for electrical power generation if the cost per megawatt can be further reduced. Currently, SOFC stacks are replaced too frequently to be cost competitive. SOFC service life can be extended by preventing chromium- (Cr-) bearing species from evaporating from the interior surfaces of balance of plant (BOP) components and poisoning the cathode to increase the lifetime. We have developed yttria-stabilized zirconia (YSZ) and aluminum oxide- (Al2O3-) modified sol-gel paints or inks for coating BOP components. 430 stainless steel (430SS) substrates with three surface conditions were coated with the 0.8–1.5 µm thick YSZ and Al2O3paints. The coated 430SS samples were tested for thermal cycling resistance, thermal soak, and Cr evaporation. Thermal soak and thermal cycling test results show promise for the YSZ-coated 430SS substrates. The Cr evaporation test of a coated substrate showed a 51% reduction in Cr generation, when compared with a bare substrate.

Tailoring the pore structure of cathode supports for improving the electrochemical performance of solid oxide fuel cells

Two types of lanthanum doped strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) composite cathodes were prepared, one with the finger-like straight open pores by the phase inversion tape casting, and the other with the randomly distributed tortuous pores by the conventional tape casting. A gas permeation flux of 42.5 × 105 Lm−2 h−1 was measured under a trans-membrane pressure of 0.6 bar for the former while only 10.6 × 105 Lm−2 h−1 for the latter. Fuel cells supported on the as-prepared LSM-YSZ composite cathodes were fabricated, comprising a 15 μm thick YSZ electrolyte layer and a 20 μm thick NiO-YSZ anode. The electrochemical performance of the fuel cells was measured using H2 as fuels and air as oxidants. The cell supported on the phase-inversion derived cathode showed a maximum power density of 362 mWcm−2 at 850 °C, while only 149 mWcm−2 for the cell supported on the cathode formed by the conventional method. The difference in the electrochemical performance between the two cells can be attributed to the pore structure of the cathode supports. It is concluded that the phase inversion tape casting provides a simple and effective approach for tailoring the pore structure of the cathode support and thus enhancing the electrochemical performance.

Effects of Current Collector Materials on Performances of Micro-Tubular Solid Oxide Electrolysers for Splitting CO2

As renewable energy sources are inherently intermittent, their increasing contributions to electricity grids will necessitate large-scale energy storage to balance supply and demand. Storing electrical energy in chemical bonds by electrolysis of CO2 and / or H2O is one option to achieve this. We chose solid oxide reactors for this application, inter alia, because in principle they can be operated cyclically in electrolyser (SOE) and fuel cell (SOFC) modes. Results will be presented of measurements of ohmic and electrode polarization resistances and global performances for CO2 splitting to CO and O2 in micro-tubular solid oxide electrolysers (SOEs), with different types of current collectors; electrolysis of steam and (CO2 + steam) exhibited similar behaviour. Silver or nickel wire current collectors, with and without silver or nickel paste, were used to contact the 220 μm thick inner lumen Ni-YSZ electrode (SOE cathode) of micro-tubular solid oxide electrolysers [1] (SOEs: Ni-YSZ|YSZ|YSZ-LSM|LSM) incorporating 34 μm thick yttria-stabilized zirconia (YSZ) electrolyte, and 40 μm thick lanthanum strontium manganite (LSM, SOE anode), as described previously for CO2 reduction [2]. Silver wire and paste was used as the current collector for the LSM electrode. As shown in Fig. 1, the best performance (ca. 1 A cm-2 at 1.5 V (thermo-neutral potential difference) at 800 °C) was achieved for reactors with nickel wire current collectors alone, implying metallic pastes had no net beneficial effects on area-specific ohmic resistances. Furthermore, applying silver paste had a detrimental effect on the Ni cathode polarization resistance, for reasons that will be presented. Fig. 2 shows polarization and ohmic resistance data at open circuit; similar behaviour was exhibited with potential differences applied to reactors. Ohmic resistances were expected to decrease by using silver wire, due to its higher electronic conductivity compared to nickel, but no stable cell performance was achieved.

Fabrication and characterization of anode supported YSZ/GDC bilayer electrolyte SOFC using dry press process

In the present paper, we fabricated and tested anode-supported solid oxide fuelcell(SOFC) with gadolinium-doped(GDC) and yttriastabilized zirconia (YSZ) electrolyte. The bilayer electrolyte thin film, consisting of a 8 μm thick YSZ layer and a 40 μm thick GDC layer, was prepared by a simple dry-pressing with simple spray coating process which is cost-effective method. The two electrolyte layers were sintered 1400°C together, and no crack and delamination at the interface were observed. An open-circuit voltage of 0.91 V and a maximum power density of over 218 mW/cm2 were measured with 3% H2O-H2 as fuel and air as oxidant at 600°C. The result shows that the electronic conductivity of GDC electrolyte was blocked by the thin YSZ electrolyte functional layer.

Corrosion Protection Performance of YSZ Coating on AA7075 Aluminum Alloy Prepared by Aerosol Deposition

Yttria stabilized zirconia (YSZ) coating was deposited on AA7075 aluminum alloy by aerosol deposition (AD) at room temperature, and its electrochemical corrosion properties were investigated in 0.5 M H2SO4, 3.5 wt% NaCl, and 0.1 M KOH solutions. A crack-free, dense, and ∼5 μm thick YSZ coating on Al alloy was successfully obtained by AD method. The YSZ coating was polycrystalline and composed of ∼10 nm nanocrystallites. Potentiodynamic and electrochemical impedance spectroscopy (EIS) tests indicated that the corrosion behavior in each solution was different, but the corrosion protection of the AA7075 Al alloy was significantly improved by the AD YSZ coating in all three solutions.

에어로졸 증착법에 의한 YSZ 코팅된 AA1050 알루미늄 합금의 전기화학적 부식 특성

Yttria stabilized zirconia (YSZ) coating was formed on AA1050 Al alloys by aerosol deposition (AD), and its electrochemical corrosion properties were investigated in 3.5 wt% NaCl and 0.5M H 2 SO 4 solutions. The crack-free, dense, and ~5 μm thick YSZ coating was successfully obtained by AD. The as-deposited coating was composed of cubic-YSZ nanocrystallites of ~10 nm size. The potentiodynamic test indicated that the YSZ coated Al alloy had much lower corrosion current densities (2 nA/㎠) by comparison to uncoated sample and exhibited a passive behavior in anodic branch. Particularly, a pitting breakdown potential could not be identified in H 2 SO 4 . EIS tests revealed that the impedance of YSZ coated sample was ~10 6 Ω㎠ in NaCl and ~10 7 Ω㎠ in H 2 SO 4 , which was about 3 or 4 orders of magnitude higher than that of uncoated sample. Consequently, the corrosion resistance of Al alloy had been significantly enhanced by the YSZ coating.

Influence of rheological characteristics of YSZ suspension on the morphology of YSZ films deposited by electrostatic spray deposition

The effect of polyvinyl butyral (PVB) on the dispersion in nonaqueous yttria stabilized zirconia (YSZ) suspension and the influence of rheological property of the YSZ suspension on morphology of deposited films by electrostatic spray deposition (ESD) were investigated. The results showed that a gradual increase of PVB (5 wt.%, 10 wt.%, 15 wt.%) enabled the suspension to be more viscose. Also, adding PVB helped to better get dispersed and decrease the size of agglomerated particles (580 nm with 5 wt.% PVB, 830 nm with 10 wt.%, and 910 nm wt.% with 15 wt.%, respectively) compared to when YSZ suspension does not contain PVB. The dense 5 μm thick YSZ film was obtained at 15 wt.% PVB suspension, and this optimal condition resulted from the optimized viscosity and the steric stabilization of suspension.

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.

Series Connection of Thick-Film (<20 μm) Electrolyte-Supported Solid Oxide Fuel Cells

Thick-film electrolyte (<20 μm)-supported solid oxide fuel cells (SOFCs) have the advantages of both electrolyte-supported and anode-supported cells due to their thin and self-supporting electrolyte layer. A multicell stacking design using a series connection of thick-film electrolyte-supported cells was adopted to avoid the bipolar plates of planar SOFCs. The cell structure of series-connected electrolyte-supported SOFCs (SES-SOFCs) is similar to the segmented-in-series SOFC design but is based on the self-supporting electrolyte. Two cells with 16 μm thick yttria-stabilized zirconia electrolytes connected in series achieved high performance, i.e., open-circuit voltage of 2.10 V and maximum power density of ∼460 mW/cm 2 at 800°C.

Investigation of the Structural and Catalytic Requirements for High-Performance SOFC Anodes Formed by Infiltration of LSCM

Composites formed by infiltration of 45 wt % La 0.8 Sr 0.2 Cr 0 .5 Ma 0.05 O 3 (LSCM) into a 65% porous yttria-stabilized zirconia (YSZ) scaffold were investigated in order to understand the reasons this material is able to provide excellent anode performance in solid oxide fuel cells (SOFCs). Scanning electron microscopy showed that the LSCM forms a film over the YSZ after calcination at 1473 K but that this film undergoes cracking to expose a long three-phase boundary after reduction at 1073 K. Coulometric titration demonstrated that the reduction of LSCM and La 0.8 Sr 0.2 MnO 3 occurred over a similar range of P(O 2 ) and that reduction is the likely cause for film cracking. To achieve low anode impedances in humidified H 2 at 973 K, it was necessary to add a catalyst. The addition of 0.5-1 wt % Pd, Rh, or Ni was sufficient to increase the maximum power density of SOFCs with 60 μm thick YSZ electrolytes to >500 mW/cm 2 in humidified H 2 at 973 K. The addition of either 1 wt % Fe or 5 wt % ceria also improved power densities but to a lesser extent. Finally, the use of Pt paste as the current collector increased performance to a similar extent as intentionally adding catalyst, showing the importance of using inert materials in electrode testing.

Thick-film electrolyte (thickness

A novel design of solid oxide fuel cell (SOFC) which utilizes a thick film (<20 μm) as an electrolyte support is developed and tested. The sintered 16 μm-thick yttria-stabilized zirconia (YSZ) electrolyte film is mounted on a 1-mm thick YSZ ring by sintering the two pieces together. With this new configuration, it is possible to fabricate a thick (<20 μm) electrolyte-supported SOFC and measure the power density of the unit cell. With LSCF (La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ ) as a cathode and Ni–YSZ as a composite anode, the cell with a 16 μm-thick YSZ electrolyte achieves a high performance, i.e., a maximum power density of 590 mW cm −2 at 800 °C. This value is comparable with that of most anode-supported SOFCs using YSZ electrolytes.

Thin yttria-stabilized zirconia electrolyte and transition layers fabricated by particle suspension spray

In order to develop high performance intermediate temperature (<800 °C) solid oxide fuel cells (SOFCs) with a lower fabrication cost, a pressurized spray process of ceramic suspensions has been established to prepare both dense yttria-stabilized zirconia (YSZ) electrolyte membranes and transition anode layers on NiO + YSZ anode supports. A single cell with 10 μm thick YSZ electrolyte on a porous anode support and ∼20 μm thick cathode layer showed peak power densities of only 212 mW cm−2 at 700 °C and 407 mW cm−2 for 800 °C. While a cell with 10 μm thick YSZ electrolyte and a transition layer on the porous anode support using a ultra-fine NiO + YSZ powder showed peak power densities of 346 and 837 mW cm−2 at 700 and 800 °C, respectively. The dramatic improvement of cell performance was attributed to the much improved anode microstructure that was confirmed by both scanning electron microscopes (SEM) observation and impedance spectroscopy. The results have demonstrated that a pressurized spray coating is a suitable technique to fabricate high performance SOFCs and at lower cost.

Direct EPD of YSZ Electrolyte Film onto Porous NiO-YSZ Composite Substrate for Reduced-Temperature Operating Anode-Supported SOFC

Electrophoretic deposition (EPD) was used for the fabrication of anode-supported yttria-stabilized zirconia (YSZ) electrolyte films. For the EPD, thin layers of graphite were pre-coated on the surface of a nonconducting porous NiO-YSZ composite anode substrate. Uniform YSZ green films were formed on the reverse sides, which did not have the graphite layers. The specimens were transformed into dense bodies ∼5 to 10 μm thick after being co-fired with the substrates. The cell performance of the ∼5 μm thick dense YSZ films supported on the anode substrates was tested using a La(Sr)Co(Fe)O 3 cathode. Maximum output power densities of ∼0.19, ∼0.61, and ∼1.02 W/cm 2 were attained at 600, 700, and 800°C, respectively.

Solid Oxide Fuel Cells Utilizing Dimethyl Ether Fuel

The feasibility and benefits of using an oxygenated fuel for solid oxide fuel cell (SOFC) operation were explored using dimethyl ether (DME). A model for the flow tube chemistry was used to predict DME gas-phase decomposition kinetics and species concentration profiles for temperatures ranging from 550 to 750°C. The predictions, which were in good agreement with mass spectral measurements, showed that in the absence of a fuel cell DME decomposed primarily into equal amounts of and CO above about 675°C. The same decomposition species were observed in catalytic reaction experiments at Ni-based anodes, but the mole fractions of the decomposition gases were much higher, between 550 and 650°C. Current-voltage measurements were made using SOFCs with 100 μm thick yttria-stabilized zirconia electrolyte supports, cathodes, and 50 vol % Ni-based anodes. Maximum power densities for SOFCs supplied directly with DME fuel were 0.10 and at 600 and 700°C, respectively. No carbon deposition was observed in cells operated at temperatures up to 700°C. © 2002 The Electrochemical Society. All rights reserved.

Increased solid-oxide fuel cell power density using interfacial ceria layers

Solid-oxide fuel cell power densities typically drop rapidly as the operating temperature is decreased, due to electrolyte ohmic losses and/or electrode overpotentials. In this paper, we describe fuel cells utilizing 8 μm thick yttria-stabilized zirconia (YSZ) electrolytes to provide low ohmic loss. Adding thin porous yttria doped ceria (YDC) layers on either side of the YSZ yielded much-reduced interfacial resistances at both the LSM cathodes and Ni–YSZ anodes. The cells provide higher power densities than previously reported below 700°C, e.g. 300 and 480 mW cm −2 at 600 and 650°C, respectively (measured in 97%H 2+3%H 2O and air), and also provide high power densities at higher temperatures, e.g. 760 mW cm −2 at 750°C.