Yttria-stabilized Zirconia Pellet Research Articles

Dispersal of high-burnup fuel fragment surrogate particles during and after loss-of-coolant accident tests

The issue of fuel fragmentation, relocation, and dispersal is critical in the licensing and use of high-burnup (>62GWd/MTU) nuclear fuel in light water reactors (LWRs). In this work, two test series are reported that examine the fragment dispersal during a burst event and an additional dispersal following the burst due to vibrations in the rod, such as those induced by accident recovery systems. To examine dispersal during the balloon and burst portion of a Loss-of-Coolant Accident event, HfO2 fragments and yttria-stabilized zirconia pellets were filled into an as-fabricated cladding tube, which was then pressurized and subjected to loss-of-coolant accident testing in steam. Results from this test were found to be highly non-prototypic, and dispersal was both significantly more violent and significantly greater in magnitude than identified for actual fuel tests. These findings were attributed to the conservative (more dispersive) nature of the particles chosen for dispersal and to the details of the test conditions used that led to particularly wide bursts. The second set of tests examined dispersal following the burst when vibrations were induced in the rod, primarily via recovery activities such as Emergency Core Cooling System actuation leading to rapid water addition. Post-burst dispersal testing was performed by inducing sinusoidal oscillations with 2–25 nm peak-to-peak amplitude and 2–5 Hz frequencies in pre-burst rods that had been refilled with HfO2 fragments or high-burnup fragment surrogate mixture of HfO2 fragments and yttria-stabilized zirconia sands. Testing revealed that rods with large burst openings (7 mm wide in this work) led to unmitigated dispersal from above the burst zone but that smaller bursts (5 mm wide), although still much larger than the mean fragment size of 3 mm, led to effectively no dispersal because of interparticle locking. Additionally, mixture and moisture were found to impact the amount of dispersal: mixtures increased dispersal, and moisture drastically reduced it. The implications of these findings on likely dispersal from actual fuel are discussed.

Gas‐Phase Photoelectrocatalysis Mediated by Oxygen Ions for Uphill Conversion of Greenhouse Gases

AbstractThe present study reports a gas‐phase photoelectrochemical (GPEC) system in which photoanode and photocathode materials are coated on each side with a pellet of the oxygen‐ion conductor yttria‐stabilized zirconia (YSZ), where light irradiation is feasible on both sides. As a model gas‐phase reaction, we chose dry reforming of methane (DRM), which converts greenhouse gases into valuable syngas. Consequently, the stoichiometric DRM reaction proceeded in our GPEC system, indicating that the oxygen ions in a YSZ pellet act as mediators to link the redox reactions. It was also noted that UV light irradiation on the anodic side was more effective than that on the cathodic side, suggesting that the photogenerated holes in the anodic YSZ side activate methane molecules, while photogenerated electrons are injected into Rh nanoparticles to cause carbon dioxide reduction in the cathodic side. Our GPEC system converts greenhouse gases into valuable syngas by light irradiation.

Effect of boundary conditions on reduction during early stage flash sintering of YSZ

The onset of flash sintering is generally considered to be predominantly a function of the conductivity of a given ceramic, the furnace temperature, and the electric field. However, the evolution of the point defect profiles in ionic conductors such as yttria-stabilized zirconia (YSZ) can complicate the picture of homogeneous Joule heating and thermal runaway during DC flash sintering. Here, 8 mol% YSZ pellets were partially flash sintered under a DC bias using various current densities and hold times. The electrode geometry was varied to modulate the oxygen ion flux available to the cathode to compare the effects on the resulting oxygen vacancy inhomogeneity. The contribution from fundamental and experimental factors to the cathodic reduction reaction is also discussed, such as interface reaction kinetics and sample geometry. Local reduction of the ceramic was inevitably observed under all current densities and the resulting microstructural inhomogeneity was explained as the result of a transient conductivity asymmetry. This asymmetry was the result of the enhanced electronic conductivity in the cathode region to a value significantly greater than the ionic conductivity of near-stoichiometric YSZ. The link between the local conductivity, voltage and Joule heating is mathematically demonstrated to result in an asymmetric heating profile.

Investigating the effect of material microstructure and irradiation temperature on the radiation tolerance of yttria stabilized zirconia against high energy heavy ions

Yttria stabilized zirconia pellets with different crystallite sizes were irradiated with 80 MeV Ag6+ ions at room temperature and 1000 K to understand the effect of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high energy heavy ions [where electronic energy loss (Se) dominates]. XRD and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage when compared with the bulk-like sample. A reduction in the irradiation damage, i.e., improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the nano-crystalline samples compared with the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against Se, was thus found to be critically dependent on the interplay between the irradiation temperature and the crystallite size. These results are explained on the basis of the “in-elastic thermal spike” model by taking into consideration the combined effects of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling strength and the lattice thermal conductivity and hence on the resulting thermal spike. These results, besides being crucial from the fundamental prospect of comprehending the size and temperature dependent radiation damage against Se, may also be important from the perspective of designing highly nano-crystalline materials for applications in various radiation environments.

Nanoparticles Infiltration into SOFC Cathode Backbones

The last decade reveals the high potential of Solid oxide cells (SOC) as hydrogen battery storage operating to the demand either under fuel cell (concept gas-to-power) or electrolysis (concept power-to-gas) profiles. Such types of ceramic-based cells usually operate beyond 750°C in order to keep reasonable electrical performances and reliability of the whole electrochemical device. But, the high interest is to reduce the operating temperature in order to limit ageing parameters (Cr contamination, metal corrosion…) and improve energy efficiency while promoting cheaper materials and system processing. Actually, O2--conducting SOC suffers to an insufficient activity of the oxygen electrode and electrical performances at lower operation temperature. In such context, Protonic Ceramic Cell technology can overcome such technical hurdle below 700°C while taking benefit to produce water at the air electrode side, avoiding the dilution of the fuel. Proton Conducting Ceramic Cell technology is now widely investigated for a variety of applications, in particular fuel cell, steam electrolysis and hydrogen separation but such technology has to face to the lack of Technology Readiness Level for a viable way of market. From those bottlenecks raised two research strategies developed at EIFER: the improvement of anionic oxygen electrodes and the up-scaling and maturation of protonic ceramic cells. The infiltration of nanoparticles into a specific backbone could theoretically improve the electrochemical performance of the air electrode. It consists of the elaboration of a precursor’s solution which is then impregnated into the porosity of the electrode. The loading amount of the promoters have been optimized to decrease the polarization area specific resistance (ASRpol) and improve performance of intermediate temperature SOCs. Three different backbone materials were coated onto Yttria-stabilized zirconia pellets: La0.8Sr0.2MnO3 (LSM), Sm0.2Ce0.8O2-δ (SDC) and Nd1.95NiO4+δ (NdN). Several compositions were studied as promoter infiltrated inside the backbones: Sm0.5Sr0.5CoO3-δ (SSC), Sm0.2Ce0.8O2-δ (SDC), CeO2, Nd1.95NiO4+δ (NdN), Pr1.97NiO4+δ (PrN), and La0.8Sr0.2MnO3 (LSM). The infiltration loading and protocol were optimized to lower as much as possible the polarization resistances. For a temperature of 700°C, the lowest ASRpol was measured on a PrN promoter impregnated inside a NdN backbone (ASR=0.26 Ω.cm2), within the literature ASRs range[i],[ii] (see Figure 1).The elaboration of protonic ceramic cell has been deeply investigated in EIFER to improve the manufacturing process, increase the performance and the size of the cell and then to reach a higher TRL. Our group validated promising results on the elaboration and electrochemical characterization of middle-scaled protonic cells (until 20 cm²)[iii][iv][v], achieving interesting performances in fuel cell and electrolysis mode (P=0.25 W.cm-2 at E=0.8V and i=-0.35 A.cm-2 at E=1.2V respectively, at 700°C) and performed long-term test (> 3000 hours) under various profiles such as fuel cell (micro-cogeneration cycles), electrolysis (evaluation of operating conditions) and reversibility (fuel cell/electrolysis).The final target of this work is to merge both research strategies to improve performances of Protonic Ceramic Fuel Cells. The results will be discussed. [i] Shen, J., et al., Improved performance of a symmetrical solid oxide fuel cell by swapping the roles of doped ceria and La0.6Sr1.4MnO4+δ in the electrode, Journal of Power Sources, 2017, 342: p. 644-651. [ii] Shao, L., et al., Nanostructured CuCo2O4 cathode for intermediate temperature solid oxide fuel cells via an impregnation technique, Journal of Power Sources, 2017, 343: p. 268-274. [iii] Dailly, J., BCY-based proton conducting ceramic cell: 1000 h of long term testing in fuel cell application, Journal of Power Sources, 2013, 240: 323-327. [iv] Dailly, J., Evaluation of proton conducting BCY10-based anode supported cells by co-pressing method: Up-scaling, performances and durability, Journal of Power Sources, 2014, 255: 302-307. [v] Marrony, M., Elaboration of intermediate size planar proton conducting solid oxide cell by wet chemical routes: A way to industrialization, Solid State Ionics, 2015, 275: 97-100. Figure 1

Influence of the electrode/electrolyte interface structure on the performance of Pr0.8Sr0.2Fe0.7Ni0.3O3-δ as Solid Oxide Fuel Cell cathode

The effect of gadolinium-doped ceria (GDC) interlayer on the Pr0.8Sr0.2Fe0.7Ni0.3O3-δ (PSFN8273) cathode performance and stability in solid oxide fuel cell (SOFC) operating conditions is investigated. Two different symmetrical half-cells, with dense GDC electrolyte pellet (GDC/PSFN cell) and with GDC interlayer deposited on yttria stabilized zirconia pellet (YSZ) (YSZ/GDC/PSFN cell), are prepared and characterized by electrochemical impedance spectroscopy (EIS) as a function of temperature. The fitting of the data is carried out using an adapted Equivalent Circuit (EC). The polarization resistance (Rp) is higher for the YSZ/GDC/PSFN cell compared to GDC/PSFN cell. This increase is assigned to the interface microstructure. Then, the electrochemical properties of the half-cell with GDC interlayer are measured in three-electrode configuration under dc cathodic overpotential. In addition, the long-term stability is evaluated through an ageing test applying a current density of −123mA.cm−2 for 1000hours at 700°C under air. PSFN8273 appears to be stable as cathode with a decrease in overpotential of about 6% in the first 200hours and a subsequently stabilization. These results mean that even if the GDC interlayer affect the cathode performance (in terms of Rp) it did not influence its stability, making PSFN8273 a suitable material as cathode for SOFC application.

Effect of the thickness of sputtered gadolinia-doped ceria as a cathodic interlayer in solid oxide fuel cells

Sputtered gadolinia-doped ceria (GDC) film was introduced as the cathodic interlayer between an yttria-stabilized zirconia (YSZ) pellet and a Pt cathode in solid oxide fuel cells (SOFCs). The fuel cells with none, 50, 100 and 150nm thick GDC interlayers were fabricated to investigate the effect of the thickness of the GDC interlayer. The performances of the SOFCs with the 100 and 150nm thick GDC interlayers operated at 450°C showed the highest performance. Through electrochemical impedance analysis, it was visualized that the GDC interlayer significantly reduced the faradaic resistance of the SOFC. The degradation of the performance from the increased ohmic resistance by adding the GDC interlayer was negligible. From the topographical images scanned by atomic force microscope, it was observed that the 50nm thick GDC interlayer did not perfectly cover the surface of the YSZ pellet, resulting in incomplete performance enhancement by the sputtered GDC.

X-ray absorption spectroscopy studies on the carbothermal reduction reaction products of 3 mol% yttria-stabilized zirconia

Extended X-ray absorption spectroscopy (EXAFS) at the ZrKedge has been used to determine changes in various bond lengths in 3 mol% yttria-stabilized zirconia (YSZ) during zirconium carbide (ZrC) formation. The principal objective of this study was to determine if ZrC formation at the YSZ/carbon interface alters the zirconia structure. A mixed-phase sample (YSZ and graphite) was carbothermally reduced to form ZrC. X-ray diffraction phase quantification by Rietveld analysis confirmed the formation of ∼50% ZrC in the analyzed sample volume. EXAFS data of ZrC and YSZ powders and a sintered YSZ pellet (∼96.7% density) were used as standards to compare with the carbothermally reduced sample.Ab initocalculations using these spectra quantified various Zr—O, Zr—C and Zr—Zr bond distances in the system. Best fit results revealed Zr—OI(tetragonal), Zr—O (monoclinic), Zr—Zr (tetragonal) and Zr—Zr (monoclinic) bond length values of 2.10, 2.25, 3.65 and 3.52 Å, respectively, in the YSZ powder, Zr—OI(tetragonal) and Zr—Zr (tetragonal) bond length values of 2.12 and 3.62 Å, respectively, in the sintered pellet, and Zr—C and Zr—Zr bond lengths of 2.32 and 3.33 Å, respectively, in the ZrC powder. Similar fitting procedures were carried out on the carbothermally reduced pellet, with measured Zr—O, Zr—Zr (of YSZ), Zr—C and Zr—Zr (of ZrC) bond lengths of 2.13, 3.62, 2.36 and 3.33 Å, respectively. These bond lengths indicate that the formation of ZrC in the YSZ matrix does not influence the local structure when compared to pure standards. Therefore, carbothermal reduction does not induce any apparent strain or thermally induced effects on the first and second coordination shells of Zr as measured by the X-ray absorption spectra of the carbothermally reduced sample. Interestingly, the results indicated that sintering of the YSZ powder into pellets did not result in any significant change in the Zr—O and Zr—Zr distances for tetragonal YSZ.

Shrinkage control of yttria-stabilized zirconia during ac electric field-assisted sintering

Abstract Yttria-stabilized zirconia pellets were easily and accurately sintered to a predetermined sintering level, including near full density, in an experimental arrangement consisting of a vertical dilatometer and an ac adjustable power supply. Conventional and electric field-assisted sintering steps can be combined, starting from temperatures above 800 °C and applying 1000 Hz alternating electric fields in the range 80–160 V cm −1 . A systematic comparison of the microstructures and impedance diagrams of samples conventionally and electric field-assisted sintered to the same density levels shows that the non-conventional sintering method gives significantly small grains in agreement with previous observations. The results show that this sintering method can be applied to produce materials partially sintered at any desired shrinkage level.

Coupled Metal Oxide-Doped Pt/SnO2 Semiconductor and Yittria-Stabilized Zirconia Electrochemical Sensors for Detection of VOCs

Yttria-stabilized zirconia (YSZ)-based sensors using Pt/SnO2-based sensing electrodes were fabricated and applied to detect several volatile organic compounds (VOCs) including acetaldehyde, acetone, ethanol and toluene. The whole sensor was exposed to the VOCs-contaminated air, i.e. without air reference. YSZ was prepared by coprecipitation, calcined, pelleted, and sintered at 1560°C for 12 h. The YSZ pellet was coated with two layers of porous Pt electrode, on one of which as the sensing electrode, a layer of Pt/SnO2 doped with SiO2, MoO3, CeO2 or Sm2O3 was screen printed. The oxide-doped Pt/SnO2 samples were prepared by a sol-gel method and characterized by XRD, SEM, and BET. As 5 wt% SiO2 or Sm2O3 is doped onto the Pt/SnO2, the crystallite size decreases from 17 to 6 or 8 nm, respectively. An automated flow system was used for evaluating the sensors performances in presence of various VOCs of different concentrations at 350–600°C. Response/recovery times of all VOCs sensors decrease with the oxide doping. Pt/SnO2 doped with 5 wt% CeO2, compared to other oxides, shows the highest EMF responses and lowest response and recovery times to the VOCs. By increasing the Pt/CeO2/SnO2 sensing layer thickness, EMF response is enhanced and maximum response shifts to higher temperatures.

Theoretical and experimental investigations on the mechanism of carbothermal reduction of zirconia

Abstract Zirconium carbide (ZrC) is an important ultra-high temperature ceramic due to its refractory properties. It is commonly synthesized via carbothermal reduction of zirconia above 1657 °C according to the reaction ZrO 2 (s)+3C (s)→ZrC (s)+2CO (g). Contrary to this reaction, prior research indicates that carbon monoxide (CO) is the responsible species for carburizing ZrO 2 to form ZrC. To explore this reaction pathway, investigations were performed by making two mixed phase pellets with 3 mol% yttria-stabilized zirconia (YSZ) and graphite. Both had an upper half made of YSZ. The lower half of one sample consisted of finely mixed YSZ and graphite powder whereas the other was pure graphite. Similar experiments were conducted with sintered YSZ pellets on top. After heat treatment at 1800 °C, X-ray diffraction analysis revealed higher ZrC conversion for the YSZ pellet face in direct contact with pure graphite. This contradicts the previous work as one would assume higher ZrC yield for YSZ pellet in direct contact with YSZ/graphite mix as they produce more CO upon reaction. Lastly, diffusional experiments showed conversion to be highly localized to a depth of ∼25 μm. This is in close agreement with calculations for carbon diffusion in YSZ based on a diffusion coefficient ( D )=3×10 −14 m 2 /s, which confirms solid–solid reaction rather than solid–gas reaction.

Development of Zirconia Based Oxygen Sensor for Lead and Lead-Bismuth Eutectic

Nanocrystalline yttria stabilized zirconia (YSZ) solid electrolyte powders of composition ZrO2-5 mol% Y2O3 were prepared through modified Pechini process and were characterized. Sintered compacts of these powders in form of pellets had 96% of the theoretical density and helium leak rate <10-9 S cc /s. Using a pellet of this electrolyte in a galvanic cell with different oxygen partial pressures across it, emf was measured as a function of temperature and thus qualified for sensor application. Towards the fabrication of the oxygen sensor for Pb and LBE loop, a compact design wherein a YSZ pellet, glass soldered to a metallic component had been chosen for the oxygen meter.

Low-Temperature Deposition of Undoped Ceria Thin Films in scCO2 As Improved Interlayers for IT-SOFC

Cerium oxide films were deposited onto various yttria-stabilized zirconia (YSZ) electrolytes using supercritical fluid deposition (SFD) in a cold wall reactor. Deposition of ceria thin films (20–240 nm) was carried out via hydrolysis of a Ce precursor at 250–300 °C (typically 30 min) in supercritical CO2 (scCO2). The as-deposited films were continuous, dense and crystalline. They exhibited some carbon contamination which was eliminated in all cases by postannealing the films at 400 °C. Film microstructure depends on the hydrolysis conditions (water to cerium molar ratio), on the substrate nature (Si wafers or YSZ pellets) and on the YSZ pellet thickness (100 μm or 1 mm). Ceria films were then used as interlayers for intermediate temperature solid oxide fuel cells (IT-SOFC) between the YSZ electrolyte and the Nd2NiO4+δ cathode layer subsequently deposited. The electrochemical properties of the SOFC symmetrical half cells were investigated by electrochemical impedance spectroscopy (EIS). The presence of the undoped ceria layer deposited in scCO2 lowers the resistance of the cell, compared both to cells with an optimized doped ceria layer deposited by screen printing and to cells without any interlayer.

Evaluation of the electrode/electrolyte contact quality in solid oxide fuel cells

Symmetrical cells have been prepared by depositing suspensions with different active powder concentrations (50% and 60% by weight respectively) of lanthanum strontium cobalt iron oxide (La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ ) on identical yttria stabilized zirconia pellets (LSCF/YSZ/LSCF). Their impedance characteristics are compared to that of a symmetrical cell with platinum electrodes deposited on a similar zirconia pellet (Pt/YSZ/Pt). The LSCF cells show different values of the electrolyte resistance. Referring to the electrolyte resistance obtained with the Pt cell and assuming that this value corresponds to almost perfect electrode/electrolyte contacts, it is possible to estimate the Effective Conducting Area (ECA) of the electrodes. The use of the ECA parameter allows a better comparison of the electrode polarizations.

Synthesis and characteristics of nanocrystalline YSZ powder by polyethylene glycol assisted coprecipitation combined with azeotropic-distillation process and its electrical conductivity

Nanoscale 8 mol% yttria stabilized zirconia (YSZ) powders were prepared by polyethylene glycol (PEG-1540) assisted coprecipitation coupling with azeotropic distillation drying process. The role of PEG and azeotropic-distillation on the morphology and particle size of YSZ was studied. Thermogravimetry and X-ray diffraction results showed that azeotropic-distillation could reduce the formation temperature of YSZ phase. X-ray patterns of the YSZ powders revealed that the crystallite size of the powders increases with increasing calcination temperature, which is consistent with transmission electron microscopy observations. The sintering behavior and the ionic conductivity of the pellets prepared from YSZ powders calcined at 800 °C were also studied. At sintering temperatures ≥1400 °C, more than 99% of the relative density was obtained. The alternating-current impedance spectroscopy results showed that the YSZ pellet sintered at 1450 °C has ionic conductivity of 0.0726 S cm −1 at 800 °C in air. The present work results have indicated that the PEG assisted coprecipitation combined with azeotropic-distillation drying process is an alternative method to synthesize yttria stabilized zirconia powders with a high sinterability and a good ionic conductivity.

Nanocrystalline yttria stabilized zirconia by metal–PVA complexation

Nanocrystalline 8 mol% yttria stabilized zirconia (YSZ) powder was synthesized using polyvinyl alcohol (PVA) as organic precursor and acidic solutions of yttrium oxynitrite and zirconium nitrate. Complex formation was established using Fourier transform infrared (FTIR) spectroscopy and solid state 13C nuclear magnetic resonance (NMR) spectroscopy. Thermal stability of the complex was investigated by thermogravimetric analysis (TGA). X-ray diffractometry (XRD) revealed formation of cubic phase YSZ at a temperature as low as 600 °C. The lattice parameter and average crystallite size were calculated from the XRD data. Particle size of the YSZ powder was investigated through transmission electron microscopy (TEM). The band gap of the sintered YSZ pellet was measured by UV–Vis-diffused reflectance spectroscopy (DRS). AC electrical conductivity was measured in air at 1 kHz frequency using a programmable RCL meter. The activation energy was calculated from the conductivity data at different temperatures using the standard Arrhenius equation.

Kinetics of Cathodic Reaction at Porous Composite Electrode under Mixed Control of Migration and Oxygen Exchange

The oxygen reduction kinetics was investigated at the porous (LSM)–yttria-stabilized zirconia (YSZ) composite electrodes with various YSZ grain sizes by employing ac impedance spectroscopy and the potentiostatic current transient (PCT) technique. For this purpose, LSM-YSZ composite electrodes were coated on a YSZ pellet by sintering at in air. The grain size of YSZ was controlled by varying the initial particle size of YSZ. From analyses of the ac impedance spectra and the cathodic PCTs measured on the electrodes as functions of temperature and ionic conductivity, it was first recognized that the overall cathodic reaction is mainly controlled by the oxygen-exchange reaction coupled with ion migration at low operating temperatures below . Second, from the discrete Fourier transformation analysis of impedance spectra, it was confirmed that the distribution of relaxation times for oxygen-ion migration becomes wider with increasing YSZ grain size in the range from due to the larger effective migration length . Finally, from the theoretical and experimental analyses of the cathodic PCTs based upon the equivalent circuit in consideration of the relaxation time distribution for ion migration, it is suggested that as the YSZ grain size decreases, the higher density of the three-phase-boundary (TPB) length leads to an increase in the overall current density and a reduction in the time to reach the steady-state current density , thus causing high power density.

Ag–Cu–Ti Braze Materials for Sealing SOFCs

Two Ag–Cu–Ti brazing alloy compositions were studied as gas seals for solid oxide fuel cells (SOFCs). Yttria-stabilized zirconia pellets were bonded using Ag–35.25Cu–1.75Ti (Cusil-ABA) or Ag–20.1Cu–1.0Ti (average composition; Ag-Cusil). Both as-brazed filler metals contained metallic Ag and Cu phases, along with continuous titanium oxide layers at the filler metal-zirconia interfaces. The brazed joints were then aged at 700°C for up to 100h in air or while separating H2 and air atmospheres. After annealing in air for 100h at 700°C, degradation in microstructure and hermeticity was more pronounced in Cusil-ABA. However, in H2-air atmosphere, Cusil-ABA performed better than Ag-Cusil. Ag-Cusil aged in H2 air delaminated from zirconia and its microstructure showed large interconnected pores in Ag-rich regions. The results were confirmed by single-cell tests using each filler metal as a gas seal. Observations of the post-test Cusil-ABA microstructure revealed little degradation. These results indicate that Cusil-ABA is better suited than Ag-Cusil as a SOFC gas seal.

Performance and Activation Behavior of Surface-Doped Thin-Film La0.8Sr0.2MnO3 − δ Cathodes

(LSM) film electrodes of thickness 100, 450, 650, and were fabricated on yttria-stabilized zirconia (YSZ) electrolyte pellets by ultrasonic spray pyrolysis. In addition, thick LSM electrodes with a surface doped with La-, Sr-, or Mn-nitrate were studied. Electrodes were deposited on both sides of the YSZ pellets in a symmetric arrangement. The individual electrode impedance spectra were measured at in laboratory air using a reference electrode placed on the free electrolyte surface. The open-circuit polarization resistance of the pure LSM and Sr and Mn surface-doped electrodes decreased significantly after initial application of cathodic current. In contrast, the La-doped sample showed no activation, with an initial polarization resistance similar to the activated, undoped LSM film. This indicates that surface La species play an important role in LSM electrode activation. All of the electrodes showed a strong, nonlinear decrease in polarization resistance accompanied by a linear decrease in ohmic resistance with increasing applied cathodic current. These changes are attributed to the introduction of a bulk-ion-transport path in the LSM film due to reduction of LSM under polarization. A minimum polarization resistance of was measured for the La surface-doped thick electrode at .

Effects of pre-calcined YSZ powders at different temperatures on Ni–YSZ anodes for SOFC

The particle size distribution and the specific surface area of yttria stabilized zirconia (YSZ) powders could be changed by pre-calcining. Accordingly, the performances of Ni–YSZ cermet might be changed too. In this paper, the effects of pre-calcined YSZ powders on Ni–YSZ cermet were investigated. The performances of Ni–YSZ cermet, including the basic physical characterization, sintering shrinkage and electrochemical properties, were studied in connection with the quality of YSZ powders pre-calcined at 900 °C, 1100 °C and 1200 °C, respectively. The results indicated that the crystal structure was not changed, but the porosity of open holes in NiO–YSZ pellets was increased with the pre-calcining temperature increasing. In addition, the total shrinkage of different anode materials was changed by using different YSZ powders, the value of Ni–YSZ cermet doping with YSZ pre-calcined at 900 °C and 1100 °C was closer to that of YSZ electrolyte. The cermet with YSZ powders pre-calcined at 900 °C showed the highest electric conductivity, and its polarization performance was closed to that of cermet with raw YSZ powders.