Ceria-doped Zirconia Research Articles

Performance and Stability of Doped Ceria–Zirconia Catalyst for a Multifuel Reforming

In the present work, the catalytic behavior of nickel-based catalysts supported on ceria/zirconia, undoped and doped with lanthanum and neodymium (3.5Ni/Ce0.8La0.5Nd0.2Zr0.13O2−x), was investigated under different reactions: steam reforming, partial oxidation and autothermal reforming of different fuels (methane, biogas, and propane). The catalytic properties of these catalysts were evaluated at a temperature of 800 °C, under atmospheric pressure, at GSHV = 120,000 h−1, using steam/carbon and oxygen/carbon ratio, respectively, of S/C = 2.5 and O/C = 0.5 and, in the case of autothermal conditions, with the addition of H2S (100 ppm) as a contaminant. Depending on the tested fuel, ATR, SR, and POX reactions over doped and undoped catalysts showed different results. In particular, the doped catalyst, due to neodymium and lanthanum doping, better distributed nickel species on the catalyst surface, promoting a higher concentration of defect groups and oxygen vacancies. This resulted in improved catalytic performance and resistance to deactivation. Endurance catalytic test also confirmed the beneficial effect of the doped catalysts.

Effects of Hydrothermal Treatment on Mesopore Structure and Connectivity in Doped Ceria-Zirconia Mixed Oxides.

Pore size and pore connectivity control diffusion-based transport in mesopores, a crucial property governing the performance of heterogeneous catalysts. In many cases, transition-metal oxide catalyst materials are prepared from molecular precursors involving hydrothermal treatment followed by heat treatment. Here, we investigate the effects of such a hydrothermal aftertreatment step, using an aqueous ammonia solution, on the disordered mesopore network of CexZr1-x-y-zYyLazO2-δ mixed oxides. This procedure is a common synthesis step in the preparation of such ceria-based oxygen storage materials applied in three-way catalysis, employed to improve the materials' thermal stability. We perform state-of-the-art Ar-physisorption analysis, especially advanced hysteresis scanning, to paint a detailed picture of the alterations in mesopore space caused by the hydrothermal aftertreatment and subsequent aging at 1050 °C. Furthermore, we investigate the network characteristics by electron tomography in combination with suitable statistical analysis, enabling a consistent interpretation of the desorption scans (physisorption). The results indicate that the hydrothermal aftertreatment enhances the mesopore connectivity of the continuous 3D network by widening pores and especially necks, hence facilitating accessibility to the particles' internal surface area and the ability to better withstand high temperatures.

The influence of cerium oxide content on the crack growth in zirconia ceramic materials for engineering applications

This article proposes a method of using cerium oxide and zirconium oxide to prepare ceramic materials for cold welding equipment in the production of lithium batteries. Injecting ceria and other metal oxides can transform zirconia from martensite into a stable four cubic lattice. By increasing the content of cerium oxide above 9%, the monoclinic crystal is transformed to tetragonal phase, and further increase to 10%–15% is beneficial to transform the tetragonal crystal state or the cubic crystal phase into a complete solid solution. When cooled from a high temperature (2293 °C) to room temperature, ceria-doped zirconia presented a tetragonal phase structure without changing into a monoclinic phase. It was also demonstrated that the crack tip at the front of the material has a shielding effect on the tetragonal phase. In particular, it was found that the flexural strength of the material reached 800 MPa, indicating that the developed zirconia-based ceramic composite material has the ability to replace diamond knives. The current work has confirmed the possibility of obtaining new ceramic materials with different characteristics by reasonably distributing the ingredients and appropriately controlling the content of cerium oxide or other metal oxides.

Changes in properties of scandia-stabilised ceria-doped zirconia ceramics caused by silver migration in the electric field

Silver is one of the most promising cathode materials for low temperature (300–500 °C) solid oxide fuel cells. The most important disadvantage of silver is its migration in the electric field. For better understanding of this phenomenon, an in situ observation of the migration mechanism was undertaken with the use of high-temperature microscopes. Scandia stabilised ceria doped zirconia CeScSZ electrolyte prepared from commercial powder was examined before and after silver migration experiments using scanning electron microscope. X-ray diffraction, broadband electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. The silver electrodes for solid oxide fuel cells were prepared using magnetron sputtering. The described cells under polarisation were examined using a high-temperature low energy electron microscope. Reference cells and post-mortem cells were observed using a scanning electron microscope equipped with high temperature stage. Under polarisation, silver moved inside the electrolyte and along the surface towards the region between electrodes. The structures thus formed were similar to those previously described in the literature; however, direct observation of the deposit growth was unsuccessful. In situ scanning electron microscopy observations of the silver electrode at 650 °C revealed neither melting of the smallest silver particles nor movement of silver structures. Silver migration through the electrolyte caused a reduction in grain interior conductivity of the electrolyte, whereas its grain boundary conductivity remained unaffected.

(Invited) Zirconia Doped Ceria As a Mixed Ion and Electron Conductor

Introduction of zirconia into ceria is known to increase the oxygen vacancy concentration in the host fluorite, despite the fixed tetravalent state of zirconium. Here we use 4-probe conductivity and electrical conductivity relaxation (ECR) methods over a wide range of oxygen partial pressures and several temperatures to explore the implications of this behavior on the transport of ionic and electronic species as a function of Zr content, up to ~ 45 mol %. All materials studied display predominantly n-type electronic conductivity, with a strongly increasing electronic conductivity with increasing Zr content. The ionic conductivity also increases with Zr concentration, but only moderately, and accordingly, the electronic transference number increases. Despite higher electronic and ionic conductivities, the bulk chemical diffusion of oxygen in ceria-zirconia is comparable to that in ceria. Furthermore, the surface reaction constant is dramatically decreased upon Zr doping. The connections between these and related observations are discussed.

The Reduction Properties of M–Doped (M=Zr, Gd) CeO2/YSZ Scaffolds Co–Infiltrated with Nickel

AbstractIn recent years infiltration of materials into porous ceramic scaffolds has been shown to be an effective way of creating catalytically active components for solid oxide fuel cells (SOFCs). However, the redox properties of these novel structures are not well understood. Here, we use X‐ray photoelectron spectroscopy (XPS) and in‐situ Raman spectroscopy to investigate the oxidation properties of yttria‐stabilised zirconia (YSZ) scaffolds infiltrated with ceria (CeO2), gadolinium‐doped ceria (GDC) and zirconia‐doped ceria (ZDC), with and without Ni. XPS shows that doping ceria with zirconia increases the ratio of Ce3+ to Ce4+, while gadolinium doping results in a decrease of Ce3+. The presence of Ni increases the Ce3+/Ce4+ ratio for CeO2 and GDC, but had little effect on ZDC. We used the shift of the F2g Raman peak to monitor in‐situ, the oxidation state of ceria. In the as‐made compounds, we show that while the gadolinium and zirconium dopants significantly change the oxidation characteristics of ceria, the resulting materials are only significantly reduced above 500 °C when co‐infiltrated with Ni. In‐situ Raman monitoring during reduction as a function of temperature showed that while ZDC reduces much more readily than undoped ceria or GDC, the presence of Ni dominated the reduction dynamics.

Zirconia Doped Ceria Cathodic Interlayer By Atomic Layer Deposition for Low Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) has the advantages of high energy conversion efficiency, fuel flexibility, and environment friendliness. However, conventional SOFC also has limitations in applying to various fields due to the high operating temperature of 800-1000℃. Therefore, low temperature SOFC (LT-SOFC) (≤ 500 ℃), which can be operated at relatively low temperature, are being widely researched these days. Operation losses of LT-SOFCs, however, have to be minimized to maintain the performance even at low temperature; especially, at low temperature, the activation loss at cathode is the dominant loss due to sluggish oxygen reduction reaction (ORR). The adoption of cathode interlayer such as doped ceria has been researched as an effective method to dramatically lower the cathodic activation loss in LT-SOFCs. In this study, we used zirconia-ceria composite cathodic interlayer fabricated by atomic layer deposition (ALD) to improve the performance of SOFC at low temperature. Ceria-based materials with high oxygen ion conductivity and high oxygen surface exchange coefficient at relatively low temperatures have been widely used as cathodic interlayers for LT-SOFCs, but the relatively low chemical stability has been the practical issue. Zirconia doped ceria (ZDC), on the contrary, is known to have better catalytic properties than pure ceria with even improved chemical stability. We show that the performance of LT-SOFC can be significantly enhanced by using ZDC as cathodic interlayer. The ZDC interlayer was deposited on the cathode side surface of yttria stabilized zirconia (YSZ) electrolyte using ALD. ALD is beneficial in depositing ultra-thin film with the capability to precisely control the composition and the thickness of films. Each interlayer of 20 nm-in-thickness was deposited with different ratios of zirconia and ceria; the molar ratio of zirconia was varied at 0, 30, 50, 80, and 100 mol%, respectively. The composition of the interlayer was analyzed by X-ray Photoelectron Spectroscopy (XPS) and the electrochemical performance was measured at 450℃ by using current-voltage characterization and electrochemical impedance spectroscopy (EIS). The maximum power density of the cell with the ZDC interlayer improved by 50% compared to that of the reference cell without the interlayer, which is even higher those of the cells with zirconia-only or ceria-only interlayers. In addition, the activation resistance of the cell with ZDC was decreased by ~50% in comparison with the cell without interlayers as shown in EIS measurements.

Structure, morphology and reducibility of ceria-doped zirconia

Zr1-xCexOx has been prepared by hydrolysis, in neutral medium, starting from rough ZrO2 and CeO2 materials as simple and cheaper synthesis method compared to sol-gel routes. The oxy-hydroxide precursors thus obtained were calcined under air at 450 °C, 900 °C and 1200 °C. The impact of those thermal treatments on the structure, texture and related redox properties has been investigated. Higher specific surface area than those observed on ceria were observed after calcination at low temperature, i.e., 450 °C. Above that temperature thermal sintering occurs having a detrimental effect on the specific surface area related to crystal growth more accentuated on CeO2. The formation of several ZrCe mixed oxide phases formed by incorporation and substitution of Zr in the structure of ceria was characterized. A complete loss of specific surface area is noticeable after calcination at 1200 °C. XRD and SEM analysis revealed the formation of two mixed oxides structure, i.e. Ce2Zr2O7.04 and Ce2Zr2O7 corresponding to different redox behavior evidenced from H2-TPR experiments.

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Redox studies on dense zirconia-doped ceria pellets were carried out by thermogravimetric investigations and dilatometry. Up to 1600 K reduction parameters determined by both methods correspond to each other. At higher temperatures, however, thermogravimetry overestimates the degree of reduction since mass loss is not only due to oxygen exsolution but also to selective evaporation of CeO2 whose vapour pressure is considerably higher than that of ZrO2. As a consequence surface segregation of zirconia occurs in (Ce,Zr)O2−δ pellets leading to a porous surface zone of Ce2Zr2O7 pyrochlore which gradually grows in thickness. Surface enrichment of zirconia is detrimental for splitting CO2 or H2O since re-oxidation temperatures of (Ce,Zr)O2−δ are known to be shifted towards lower temperatures with increasing ZrO2 content. Thus, very harsh reduction conditions should be avoided for the (Ce,Zr)O2−δ redox system. The kinetics investigations comprised the high temperature reduction step (T ≅ 1600 K) and the “low” temperature oxidation reaction with a carbon dioxide atmosphere (T ≅ 1000 K). The reduction kinetics (at around 1600 K and an oxygen activity of 7 × 10−4 in the gas phase) directly yield the (reduction) equilibrium exchange rate of oxygen in the order of 10−7 mol·O/(cm3·s) as the kinetics are surface controlled. The oxidation step at around 1000 K, however, occurs in the mixed control or in the diffusion control regime, respectively. From oxygen isotope exchange in combination with SIMS depth profiling oxygen exchange coefficients, K, and oxygen diffusivities, D, were determined for so-called equilibrium experiments as well as for non-equilibrium measurements. From the obtained values for K and D the (oxidation) equilibrium exchange rates for differently doped ceria samples were determined. Their dependency on the oxygen activity and the nature and the concentrations of a tetravalent dopant (Zr) and trivalent dopants (La, Y, Sm) could be semi-quantitatively rationalised on the basis of a master equation for the equilibrium surface exchange rate.

Migration and Stabilization of Radical Scavengers in PEFCs

Cerium ions are additives which enhance the durability of polymer electrolyte fuel cells (PEFCs) by scavenging reactive radical species which are generated during operation.1 These radicals attack vulnerable carboxyl, sulfonic acid, and ether groups in the ion conducting polymer, or ionomer, phases in the polymer electrolyte membrane (PEM) and catalyst layers (CLs) within the membrane electrode assembly (MEA) of the cell.2 During cell fabrication, conditioning, and discharge, Ce rapidly migrates between the PEM and CLs, which reduces efficiency of the Pt catalyst and may negate the addition of the Ce additive.3,4 Therefore, in order to stabilize Ce and localize it to areas of highest radical generation, it is critical to understand the relative influences of different migration mechanisms. In this work, we identified the fundamental Ce migration mechanisms during PEM fuel cell operation. Using a novel elemental analysis technique based on X-ray fluorescence (XRF), we characterized Ce migration due to potential and concentration gradients, water flux, and degradation of Ce-exchanged sulfonic acid groups within the PEM. During accelerated stress tests (ASTs), which are designed to reproduce and enhance stressors the cell will experience in the field, we have observed that < 1% of Ce exits the cell during open circuit voltage (OCV) between 30% and 100% RH. It does, however, irreversibly migrate from the PEM into the CLs at a rate correlated to AST aggressiveness. As a result, Ce accumulation in the CL reduces performance, while Ce migration out of the PEM lowers the PEM’s ability to resist the harmful effects of reactive radicals. In order to determine the relevant Ce transport coefficients during cell operation, Ce migration was induced in PEMs using H2 pump experiments under a range of applied potentials at 50% and 100% RH. Ce profiles were intermittently measured using XRF and fit with a 1-D Nernst-Planck equation. Using this model, diffusion and ion mobility coefficients were extracted, which arise due to concentration and potential gradients during the H2 pump experiments, respectively. The results show the rapid and significant effects of such gradients on Ce movement. Using this knowledge, we propose system control and additional material engineering strategies to mitigate Ce migration due to potential and concentration gradients, in order to reduce performance losses and improve cell durability. We have also determined that the degradation of Ce-exchanged ionomer side chains during aggressive ASTs results in significant Ce migration from the PEM into the CLs. In order to counter undesirable migration due to ionomer degradation, we propose the use of more efficient radical scavengers or improved localization of scavengers near areas of highest radical generation. Zirconia-doped ceria (CZO) has previously been shown to enhance peroxide reactivity while minimizing byproduct radical generation.5 We have demonstrated that adding CZO to the cathode CL, where significant peroxide and radical generation occurs6,7, results in identical initial cell polarization performance compared to CZO-free cells. During PEM chemical stability ASTs, however, CZO reduces gas crossover (Figure 1a) and fluoride emission (Figure 1b) rates, which implies that it is a more effective radical scavenger. Less ionomer degradation results in stable performance of the CZO-enhanced MEA after 500 hours of ASTs. Furthermore, after >1400 hours of ASTs, the Ce concentration in the PEM was maintained at its initial value due to the protective capabilities of CZO. Acknowledgements This research is supported by the U.S. DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium; Fuel Cells Program manager: Dimitrios Papageorgopoulos. Prof. Ajay Prasad and Prof. Suresh Advani also acknowledge support from the University of Delaware’s Fuel Cell Bus Program. This program is funded by the Federal Transit Administration at the Center for Fuel Cell Research at the University of Delaware. References Coms, F. D.; Liu, H.; Owejan, J. E. ECS Trans. 16, 1735–1747 (2008).Rodgers, M. P.; Bonville, L. J.; Kunz, H. R.; Slattery, D. K.; Fenton, J. M. Chem. Rev. 112, 6075–6103 (2012).Stewart, S. M.; Spernjak, D.; Borup, R.; Datye, A.; Garzon, F. ECS Electrochem. Lett. 3, F19–F22 (2014).Baker, A. M.; Mukundan, R.; Spernjak, D.; Judge, E. J.; Advani, S. G.; Prasad, A. K.; Borup, R. L. J. Electrochem. Soc. 163, F1023–F1031 (2016).Stewart, S. M.; Borup, R. L.; Wilson, M. S.; Datye, A.; Garzon, F. H. ECS Trans. 64, 403–411 (2014).Sethuraman, V. A; Weidner, J. W.; Haug, A. T.; Motupally, S.; Protsailo, L. V. J. Electrochem. Soc. 155, B50-B57 (2008).Gubler, L.; Dockheer, S. M.; Koppenol, W. H. J. Electrochem. Soc. 158, B755-B769 (2011). Figure 1

CeO2/ZrO2 as green catalyst for one-pot synthesis of new pyrano[2,3-c]-pyrazoles

Ceria-doped zirconia (CeO2/ZrO2)-catalyzed synthesis of pyrano[2,3-c]-pyrazoles via four-component reaction of malononitrile, hydrazine hydrate, ethyl acetoacetate, and substituted aldehydes is described. The catalytic material CeO2/ZrO2 was prepared and characterized by different techniques including powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) analysis. Twelve new pyrano[2,3-c]-pyrazole derivatives (5a–k) were synthesized in good to excellent yield (89–98%) and their structures established and confirmed by different spectroscopic methods, viz. 1H, 13C, and 15N nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). The environmental benefits of the process include excellent yield, short reaction time, simple work-up, elimination of toxic solvents, and avoidance of chromatographic separation. The CeO2/ZrO2 catalyst enables a facile synthesis procedure, is inexpensive, and has good reusability (at least six times).

Performance of a carbon monoxide sensor based on zirconia-doped ceria

Resistive-type carbon monoxide sensors were fabricated using zirconia-doped ceria, and their sensing properties were evaluated and compared with equivalent devices based on non-doped ceria. The response of both sensor types was found to increase with decreasing temperature, while the response at 450 °C of a sensor fired at 950 °C was greater than that of a sensor fired at 1100 °C. When fired at 950 °C, however, the response at 450 °C of a sensor created using zirconia-doped ceria was slightly less than that of a sensor constructed from non-doped ceria. Multivariate analysis confirmed that the response of both sensor types is proportional to the resistance raised to the power of about 0.5, and inversely proportional to the particle size raised to a power of about 0.8. The sensor response time can be considered almost the same regardless of whether zirconia doping is used or not.

Fabrication Characterization of 1Ce10ScSZ Electrolyte Prepared by Co-Precipitation and Hydrothermal Treatment for Solid Oxide Fuel Cells.

Nanocrystallite ceria-doped scandia-stabilized zirconia (1Ce10ScSZ) powders are prepared using a combination of co-precipitation and hydrothermal treatments. Power density of 1.0 W cm(-2) is obtained at 1.6 A cm(-2) and 800 °C due to the drastic reduction of ohmic and polarization resistance in the SOFC cell.

Methane steam reforming at low temperature: Effect of light alkanes’ presence on coke formation

Steam reforming of natural gas for the production of hydrogen at low operation temperature offers significant financial and environmental advantages. However, the presence of higher hydrocarbons as minor components of natural gas can significantly affect the formation of coke and thus the effectiveness of the catalyst. In this study, the effect of the presence of C2–C3 alkanes in the feedstock on the carbon accumulation during low temperature steam reforming of methane is investigated over Ni and Rh catalysts supported on lanthanum doped ceria–zirconia mixed oxide. Both catalysts showed high resistance to coke formation and especially in the case of Rh/La/CeO2–ZrO2, the carbon accumulation detected was low even after 10h on stream in steam reforming of all mixtures of hydrocarbons tested. The presence of higher alkanes in methane increased the amount of carbon on Ni(10)CeZrLa compared to pure methane as well as the nature of the carbonaceous species. Increase in the C-number of the additive alkane had almost no influence on the total amount of carbon formed (C/H feed ratio=constant) but favored the formation of filamentous carbon.

Aluminium doped ceria–zirconia supported palladium-alumina catalyst with high oxygen storage capacity and CO oxidation activity

The Ce0.5Zr0.3Al0.2O1.9/Pd-γ-Al2O3 catalyst prepared by a mechanochemical route and calcined at 1000°C for 20h in air atmosphere to evaluate the thermal stability. The prepared Ce0.5Zr0.3Al0.2O1.9/Pd-γ-Al2O3 catalyst was characterized for the oxygen storage capacity (OSC) and CO oxidation activity in automotive catalysis. For the characterization, X-ray diffraction, transmission electron microscopy and the Brunauer–Emmet–Teller (BET) technique were employed. The OSC values of all samples were measured at 600°C using thermogravimetric-differential thermal analysis. Ce0.5Zr0.3Al0.2O1.9/Pd-γ-Al2O3 catalyst calcined at 1000°C for 20h with a BET surface area of 41m2g−1 exhibited the considerably high OSC of 583μmol-Og−1 and good OSC performance stability. The same synthesis route was employed for the preparation of the CeO2/Pd-γ-Al2O3 and Ce0.5Zr0.5O2/Pd-γ-Al2O3 for comparison.

Mechanism of CH4 Dry Reforming on Nanocrystalline Doped Ceria-Zirconia with Supported Pt, Ru, Ni, and Ni–Ru

Specificity of CH4 dry reforming mechanism for Me-supported doped ceria-zirconia catalysts with high oxygen mobility was elucidated using a combination of transient kinetic methods (TAP, SSITKA) with pulse microcalorimetry and in situ FTIRS. Steady-state reaction of CH4 dry reforming is described by a simple redox scheme with independent stages of CH4 and CO2 activation. This is provided by easy CO2 dissociation on reduced sites of oxide supports followed by a fast oxygen transfer along the surface/domain boundaries to metal sites where CH4 molecules are transformed to CO and H2. The rate-limiting stage is irreversible transformation of CH4 on metal sites, while CO2 transformation proceeds much faster being reversible for steady-state surface. The oxygen forms responsible for CH4 selective transformation into syngas correspond to strongly bound bridging oxygen species with heats of desorption ≈600–650 kJ/mol O2, most probably bound with pairs of Pr and/or Ce cations able to change their oxidation state. Ni + Ru clusters could be involved in CO2 activation via facilitating C–O bond breaking in the transition state, thus increasing the rate constant of the surface reoxidation by CO2. Strongly bound carbonates are spectators.

The impact of thermal treatment conditions on the formation of crystalline structure of Ce-Zr-oxide composite obtained by a modified sol-gel technique

We present the results of the modified sol-gel synthesis of ultrafine ceria-doped zirconia powder for medical ceramics (implants) and catalytic purposes (environmental catalysis and petrochemistry). Special attention has been paid to study the influence of thermal treatment on crystallite size and crystal lattice parameters of zirconia doped by ceria. Zirconyl chloride and cerium nitrate were used as metal sources, and tetraethylammonium hydroxide (TEAH) was used as a sol stabilizer at molar ratio TEAH/Σ (Ce + Zr) equal to 0.5. It was proved that zirconium and cerium practically completely were included in the obtained solid solutions, since their phase compositions fully correspond to initial quantities of cerium and zirconium in reaction mixture. It was shown that average crystallite size of the obtained powders did not exceed 75Å, and the powders were resistant to thermal treatment. It was established that stabilization of the crystal lattice of ZrO2 occurs through formation of a cubic ceria sublattice.

Fabrication Characteristics of SOFC Single Cell Using Nanocrystalline 1Ce10ScSZ Electrolyte Powder prepared by Co-Precipitation Process

Nanocrystalline ceria-doped scandia-stabilized zirconia (1Ce10ScSZ) powders were prepared via the co-precipitation process for solid oxide fuel cell. The effects of the calcination temperature on different properties of the as-synthesized powders, such as phase evolution, crystalline size, and specific surface area were investigated. The synthesized powders calcined at 900 °C showed a specific surface area of 5 m2 g−1 and crystalline size of 28.2 nm, and ionic conductivity of 0.07S cm−1 as measured at 750 °C. An anode-supported electrolyte with a thin electrolyte layer of 6μm composed of the synthesized 1Ce10ScSZ powders was fabricated using the tape-casting and co-sintering techniques for a solid oxide fuel cell (SOFC) single cell. The open-circuit voltage of the single cell thus obtained was 1.11 V at 750 °C, indicating the dense microstructure of the electrolyte layer. A power density of 0.9W cm−2 was obtained for the SOFC single cell at 1.5A cm−2 and 750 °C. The SOFC single cell fabricated using the nanocrystalline 1CeScSZ electrolyte exhibited good performance because of the drastic reductions in the ohmic resistances.

Temperature independent resistive oxygen sensor prepared using zirconia-doped ceria powders

A resistive oxygen sensor with extremely good temperature independence within a temperature range of 923–1123K was fabricated from precipitated ceria–zirconia solid solution powders. Experimental results identified the as-precipitated powders as a nanocrystalline ZrO2-doped CeO2 (ZDC) solid solution phase. The amount of Ce3+ in CeO2 film was increased by doping with ZrO2, identified by XPS. The electrical resistance of ZDC film showed a more significant decreasing rate than that of the undoped CeO2 at lower oxygen partial pressure. An n-type semiconductance of ZDC films was obtained under oxygen partial pressures from 1.0 to <10−15atm. We selected two compositions of the ZDC films whose activation energies were approximately equal (∼1.69eV at 1.0atm and ∼1.66eV at 0.01atm) for the fabrication of temperature independent resistive oxygen sensors. ZDC films containing 10at% and 5at% ZrO2 (10ZDC and 5ZDC) were used as OMM (oxygen partial pressure measurement material) and TCM (temperature compensating material), respectively. This study confirms the conductive behaviors of ZDC at various oxygen partial pressures as a function of temperature, as well as the suitability of ZDC films for application as temperature independent oxygen sensors. The dynamic response of the resistive oxygen sensor with TCM also revealed that the sensor possessed a relatively good sensibility and stability.

Sol–gel synthesis and phase composition of ultrafine ceria-doped zirconia powders for functional ceramics

Abstract Ultrafine ceria-doped zirconia powders with the general formula CexZr1−xO2 oriented for functional ceramic materials for different purposes were prepared by modified sol–gel synthesis with use of monoethanolamine or tetraethylammonium hydroxide. All powders were high crystallized single-phase systems with average crystallite size 8–11 nm. It was established that doping of zirconia by ceria led to a decrease in the crystallite size. At the same time the nature of the zirconium salt anion has little effect on crystallite size. However, only powders obtained from zirconyl chloride had crystallites with sizes below 10 nm. When x = 0.150–0.155, a sharp increase in the crystallite size was observed regardless of the used organic components. Use of tetraethylammonium hydroxide resulted in formation of CexZr1−xO2 crystallites of 2–3 nm smaller than that which was obtained in the presence of monoethanolamine.