Thin Yttria-stabilized Zirconia Electrolyte Research Articles

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.

High performance cathode-unsintered solid oxide fuel cell enhanced by porous Bi1.6Er0.4O3 (ESB) interlayer

Dense bismuth oxides stabilized with lanthanide dopants (δ-Bi2O3) are always used as interlayer for thin layer GDC (gadolinia-doped ceria) or YSZ (yttria-stabilized zirconia) electrolyte solid oxide fuel cell to improve the cell performance. Dense ESB (Bi1.6Er0.4O3) layer preparation needs special equipment or well synthesized nano-sized powders, which is not friendly for large scale and commercial application. In this paper, anode support unsintered cathode cell with porous ESB interlayer is prepared through simple screen print and its electrochemical performance is tested. No matter sintered or not, porous ESB interlayer lowers both the polarization resistance and ohmic resistance, and enhances cell performance, especially for the ohmic resistance of unsintered cells. The cell with ESB porous interlayer and SSC (Sm0.5Sr0.5CoO3-δ)-ESB unsintered cathode achieves a peak power density of 1.329 W cm−2 at 700 °C, which is 1.61 times higher than that of the cell without ESB interlayer and 0.93 times higher than that of the sintered cell. However, the durability of porous ESB interlayer enhanced cells is not ideal and it should be improved in further works.

Production of syngas by solid oxide electrolysis: A case study

An investigation of syngas production using solid oxide electrolysis was carried out. A conventional solid oxide cell based on Ni supporting cathode, thin yttria-stabilized zirconia electrolyte, yttria-doped ceria interlayer, and strontium-doped lanthanum cobaltite and ferrite-based perovskite anode (Ni-YSZ/YSZ/YDC/LSFC) was used for the reduction of CO2 and water to syngas. This process was assisted by H2 added to the reactant in various amounts to maintain the Ni sites in a metallic state. This was necessary to favour CO2 reaction and to avoid ohmic constraints that may derive from the occurrence of Ni re-oxidation as consequence of the presence of oxidising species like CO2 and water. The outlet gas was analysed by gas chromatography. The presence of CO and CH4 beside CO2 and H2 was detected in the outlet stream. Analysis of outlet gas composition revealed that CO was produced by both electrochemical and catalytic mechanisms. Suitable CO2 conversion was achieved using dry gas.

Optimization of anode structure for intermediate temperature solid oxide fuel cell via phase‐inversion cotape casting

AbstractA functional layer and a porous support that together constitute an anode for a solid oxide fuel cell were simultaneously formed by the phase‐inversion tape casting method. Two slurries, one composed of NiO and yttria‐stabilized zirconia (YSZ) powders and the other of NiO, YSZ, and graphite were cocasted and solidified by immersion in a water bath via the phase‐inversion mechanism. The as‐formed green tape consisted of a sponge‐like thin layer and a fingerlike thick porous layer, derived from the first slurry and the second slurry, respectively. The former acted as the anode functional layer (AFL), while the latter was used as the anode substrate. The AFL thickness was varied between 20 and 60 μm by adjusting the blade gap for the tape casting. Single cells based on such NiO‐YSZ anodes were prepared with thin YSZ electrolytes and YSZ‐(La0.8Sr0.2)0.95MnO3−δ (LSM) cathodes, and their electrochemical performance was measured using air as oxidant and hydrogen as fuel. The maximum power densities obtained at 750°C were 720, 821, and 988 mW cm−2 with the AFL thickness at 60, 40, and 20 μm, respectively. The satisfactory electrochemical performance was attributed to the dual‐layer structure of the anode, where the sponge‐like AFL layer provided plenty of triple‐phase boundaries for hydrogen oxidation, and the fingerlike thick porous substrate allowed for facile fuel transport. The phase‐inversion tape casting developed in this study is applicable to the preparation of other planar ceramic electrodes with dual‐layer asymmetric structure.

Dense thin YSZ electrolyte films prepared by a vacuum slurry deposition technique for SOFCs

A novel vacuum deposition technique based on a slurry coating is proposed for the preparation of thin yttria-stabilized zirconia (YSZ) electrolyte films on a porous NiO-YSZ substrate for solid oxide fuel cells (SOFCs). The vacuum pressure not only improved the packing density of the electrolyte particles but also enhanced the bonding strength between the anode and electrolyte layers. The polarization resistance of the cell prepared via vacuum deposition decreased from 1.27 to 0.89Ωcm2, which resulted in a remarkable increase in the peak power density from 249 to 292mWcm−2 at 800°C. An anode functional layer (AFL) was also fabricated by the vacuum slurry deposition method in an attempt to increase the three-phase boundaries (TPBs) at the anode/electrolyte interface. The scanning electron microscopy (SEM) images revealed that the sintered YSZ electrolyte film has a crack-free, dense and homogeneous microstructure. These experimental results indicate that slurry vacuum deposition is an effective technique for producing dense thin films for SOFCs and other applications.

(Sensor Division Outstanding Achievement Award) Mixed Potential Sensors for Hydrogen Safety and Automotive Applications

Mixed potential sensors are a class of non-equilibrium electrochemical sensors capable of detecting the presence of reducing or oxidizing gases. These devices usually consist of two electrodes supported on an electrolyte, and exposed to a sensing gas without the need for a separate reference electrode. The potential at each of the electrode/electrolyte interfaces is determined by the rates of electrochemical oxidation and reduction reactions. Since electrode composition, morphology and sample temperature control the rates of these reactions, it is theoretically possible to select a combination of electrodes and an operating temperature to provide sensitivity and selectivity to a desired gas species. Over the past 15 years Los Alamos National Laboratory (LANL) has developed yttria stabilized zirconia (YSZ) electrolyte based mixed potential sensors for various applications. Novel 4-electrode experiments were used to unravel the working principle of these sensors and it was determined that the sensor sensitivity was primarily controlled by the rate of oxygen reduction reaction (ORR) and amount of heterogeneous catalysis of the reducing/oxidizing gas. Electrodes with poor ORR kinetics and low heterogeneous catalysis rates yielded the highest mixed potentials. This observation led to the development of dense electrode and porous electrolyte morphologies for optimal sensitivity. Furthermore, the use of dense electrodes also improved the morphological stability of these devices leading to exceptional long-term durability. The LANL sensor design is unique and does not use the dense electrolyte and porous electrodes configuration that most sensors use. In this talk the development of new techniques including thin film deposition, tape casting and high temperature ceramic co-fired (HTCC) processes for the manufacturing of these novel sensors will be discussed. While tape casting and thin film deposition yield sensors with high sensitivity and long-term durability, they are not easily scalable for low cost manufacturing. LANL, in collaboration with ESL ElectroScience, has developed a HTCC process to manufacture low cost sensors that retain the unique advantages of the LANL design. This talk will focus on the development of nitrogen oxide (NOx), ammonia (NH3) and hydrogen sensors. The sensing electrodes for the nitrogen oxide, ammonia and hydrogen sensors are La1-xSrxCrO3- d, Au and Sn1-xInxO2- d respectively. All sensors use a Pt counter electrode and the LANL patented design, where dense electrodes are partially covered with a thin YSZ electrolyte layer. While the hydrogen and ammonia sensors are operated in the open circuit mode, the nitrogen oxide sensor is operated under a current bias to minimize selectivity to hydrocarbons and improve selectivity to both NO and NO2. This talk will also discuss the evaluation of these sensors in end-user applications. Data from dynamometer testing of NOx and NH3 sensors at Oak Ridge National Laboratory’s National Transportation Resource Center will be presented. Hydrogen safety sensor data from field trials at a hydrogen fueling station in California will also be presented. Finally the barriers and hurdles for the successful commercialization of these sensors will be discussed.

Fabrication of Thin-Film Yttria-Stabilized Zirconia Electrolyte by Aerosol-Assisted Chemical Vapor Deposition

In this work, fully dense yttria stabilized zirconia (YSZ) electrolyte films under thickness of 1 μm are successfully fabricated on the anode-supported solid oxide fuel cells (SOFCs) by aerosol assisted chemical vapor deposition (AACVD), which is a type of chemical vapor deposition but conducted in an open atmospheric air not requiring expensive vacuum processes. SOFCs with thin film AACVD YSZ electrolytes marked 720 mW/cm2 at 650°C as the maximum power in our test with open circuit voltage over 1 V. We expect that this result will contribute to cost-effective production of high performance low temperature SOFCs.

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.

The potential and challenges of thin-film electrolyte and nanostructured electrode for yttria-stabilized zirconia-base anode-supported solid oxide fuel cells

Thin-film electrolytes and nanostructured electrodes are essential components for lowering the operation temperature of solid oxide fuel cells (SOFCs); however, reliably implementing thin-film electrolytes and nano-structure electrodes over a realistic SOFC platform, such as a porous anode-support, has been extremely difficult. If these components can be created reliably and reproducibly on porous substrates as anode supports, a more precise assessment of their impact on realistic SOFCs would be possible. In this work, structurally sound thin-film and nano-structured SOFC components consisting of a nano-composite NiO–yttria-stabilized zirconia (YSZ) anode interlayer, a thin YSZ and gadolinia-doped ceria (GDC) bi-layer electrolyte, and a nano-structure lanthanum strontium cobaltite (LSC)-base cathode, are sequentially fabricated on a porous NiO–YSZ anode support using thin-film technology. Using an optimized cell testing setup makes possible a more exact investigation of the potential and challenges of thin-film electrolyte and nanostructured electrode-based anode-supported SOFCs. Peak power densities obtained at 500 °C surpass 500 mW cm−2, which is an unprecedented low-temperature performance for the YSZ-based anode-supported SOFC. It is found that this critical, low-temperature performance for the anode-supported SOFC depends more on the electrode performance than the resistance of the thin-film electrolyte during lower temperature operation.

Suspension chemistry and electrophoretic deposition of zirconia electrolyte on conducting and non-conducting substrates

Suspensions of 8mol% yttria stabilized zirconia (YSZ) particulates in isopropanol medium are prepared using acetylacetone, iodine and water as dispersants. The effect of dispersants concentration on suspension stability, particle size distribution, electrical conductivity and pH of the suspensions are studied in detail to optimize the suspension chemistry. Electrophoretic deposition (EPD) has been conducted to produce thin and dense YSZ electrolyte films. Deposition kinetics have been studied in depth and good quality films on conducting substrate are obtained at an applied voltage of 15V for 3min. YSZ films are also fabricated on non-conducting NiO-YSZ anode substrate using a steel plate on the reverse side of the substrate. Upon co-firing at 1400°C for 6h a dense YSZ film of thickness ∼5μm is obtained. Such a half cell (anode+electrolyte) can be used to fabricate a solid oxide fuel cell on applying a suitable cathode layer.

Fabrication of structured anode-supported solid oxide fuel cell by powder injection molding

Powder Injection Molding (PIM) gives the possibility to produce, at an industrial rate, ceramic parts with fine details. It is thus a possible approach to reduce the fabrication costs of Solid Oxide Fuel Cells (SOFCs). This work presents fabrication and electrochemical characterization results of injection-molded structured anode-supported SOFCs.Planar anode-supported SOFCs with fine details have been produced by injection molding of a mixture of nickel oxide (NiO) and yttria-stabilized zirconia (YSZ). The channeling structure and support porosity ensure gas transport on the fuel side. Initial anode support characterizations like sintering shrinkage, porosity and electrical conductivity have been done on simple Ni–YSZ test bars. Thin YSZ electrolyte has been deposited by spin-coating on the PIM green body before half-cell co-sintering.Electrochemical testing was carried out with a lanthanum–strontium manganite (LSM)–YSZ cathode. The performance is comparable to tape-cast anode-supported cells, with 0.45 W cm−2 obtained at 0.6 V and 810 °C. Medium-term galvanostatic testing shows a degradation rate of about 1.1% kh−1. Post-test analysis with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) attribute this mainly to cathode degradation due to Cr and S poisoning. These results are therefore promising for using a PIM fabrication process in the SOFC field.

A bi-layer cathode based on lanthanum based cobalt- and iron-containing perovskite and gadolinium doped ceria for thin yttria stabilized zirconia electrolyte solid oxide fuel cells

Composite cathodes based on La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) are investigated for lower operating temperature (<750°C) applications of a solid oxide fuel cell (SOFC). To enhance a charge transfer, a bi-layer SOFC cathode is proposed, which has a LSCF–Ce0.9Gd0.1O1.95 (GDC) composite layer and a pure LSCF layer. The bi-layer cathode SOFC shows a current density of 0.65Acm−2 at 0.8V and 660°C, which is higher than a LSCF–GDC composite single-layer cathode SOFC cell of 0.35Acm−2. The charge transfer polarizations in the bi-layer cathode SOFC are 0.14Ωcm2 and 0.35Ωcm2 at 760°C and 660°C, respectively, which are lower than those in the single-layer cathode cell of 0.23Ωcm2 and 0.66Ωcm2. The impedances characterized with a fitting model show that the lowered charge transfer polarization in the bi-layer cathode is a dominant factor in reducing the total polarization of SOFC.

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.

Stainless Steel/Yttria Stabilized Zirconia Composite Supported Solid Oxide Fuel Cell

In this paper composite supports for solid oxide fuel cells were fabricated and evaluated. Substrates were composed of stainless steel and yttria stabilized zirconia (YSZ) powders mixed in different volume ratios. Their sintering behavior (linear shrinkage, resulting porosity) and high temperature properties (oxidation resistance, electrical conductivity) were evaluated. Based on those results the best composition for composite supports was selected and fuel cells were fabricated. Thin YSZ electrolytes were deposited on one side of the support and sintered at 1350 °C in pure hydrogen, while LNF (LaNi0.6Fe0.4O3) cathodes were deposited on the top of the electrolyte and fired in situ at 800 °C. The fuel cells provided power density of about 80 mWcm-2 at 800 °C. It is worth noting that this performance was achieved without adding any catalytically active phases into composite support, while at the same time the supports exhibited relatively low porosity. This demonstrates that stainless steel can serve as an anode active material. Degradation of this fuel cell was fast (12%/h), nonetheless its performance seems interesting for further investigation.

Self-Supported Thin Yttria-Stabilized Zirconia Electrolytes for Solid Oxide Fuel Cells Prepared by Laser Machining

A new procedure to fabricate self-supported thin yttria-stabilised zirconia membranes by laser machining is presented. We have used a galvanometric controlled laser beam to machine the surface of a conventional sintered YSZ plate and achieved thin areas up to 10 µm thick, but also maintaining thicker support beams to ensure the structural strength of the membrane. The outer areas of the plate are left unaltered to facilitate the sealing of the cell. This kind of thin membrane is ideal to prepare electrolyte-supported Solid Oxide Fuel Cells (SOFC) operating at low temperature. The membranes have been characterized by optical profilometry, Raman Spectroscopy and Electrochemical Impedance Spectroscopy. Using the laser machined YSZ electrolyte a conventional YSZ-Ni/YSZ/LSM planar Solid Oxide Fuel Cell has been fabricated and characterized.

Self-Supported Thin Yttria-Stabilized Zirconia Electrolytes for Solid Oxide Fuel Cells Prepared by Laser Machining

not Available.

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells: II. Role of Ni Diffusion on LSM Performance

The sintering of (LSM-20) solid oxide fuel cell cathodes (in the temperature range of ) on anode-supported cells utilizing a Ni–yttria-stabilized zirconia (YSZ) anode and a thin YSZ electrolyte ( thickness) revealed the need for a protective ceria interlayer to prevent a detrimental interaction between the YSZ and the LSM. The interaction, however, was not the typically assumed formation of insulating La- and Sr-zirconate, but rather the result of Ni diffusion from the anode through the YSZ electrolyte and into the LSM, resulting in coarsening and increased densification of the LSM microstructure. The protective layers at the cathode/electrolyte interface were effective in blocking the Ni diffusion. As an alternative to the use of a protective ceria interlayer, the presence of YSZ in the cathode material was able to suppress the coarsening of LSM, thereby significantly improving the electrochemical performance.

Low Temperature Performance Improvement of SOFC with Thin Film Electrolyte and Electrodes Fabricated by Pulsed Laser Deposition

The performance of solid oxide fuel cells (SOFCs) with thin film electrolytes and electrodes was investigated at a lower operating temperature regime . anode-supported unit cells with thin film components of a Ni–yttria-stabilized zirconia (YSZ) composite anode interlayer, a thin YSZ electrolyte, and a lanthanum strontium cobalt oxide cathode were fabricated by using pulsed laser deposition, and the performance of the cells was characterized at the temperature range of . Stable open-circuit voltage values above 1 V were successfully obtained with thin film electrolyte cells, which implied that the thick electrolyte was fairly dense and gastight. The thin film electrolyte cells exhibited a much more improved cell performance than a thick film YSZ electrolyte cell at the low operating temperature regime and, in some cases, showed better power outputs than other thin film membrane micro-SOFCs.

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.

Erratum to “Ln0.6Sr0.4Co1−Fe O3−δ (Ln = La and Nd; y= 0 and 0.5) cathodes with thin yttria-stabilized zirconia electrolytes for intermediate temperature solid oxide fuel cells” [J. Power Sources 187 (2) (2009) 480–486

Erratum to “Ln0.6Sr0.4Co1−Fe O3−δ (Ln = La and Nd; y= 0 and 0.5) cathodes with thin yttria-stabilized zirconia electrolytes for intermediate temperature solid oxide fuel cells” [J. Power Sources 187 (2) (2009) 480–486