Sm-doped CeO2 Research Articles

DFT+U calculation of Sm3+ and Sr2+ co-doping effect on performance of CeO2-based electrolyte

Solid oxide fuel cells (SOFCs) have been attracting people's attention for their high energy conversion efficiency, good fuel compatibility, no precious metal catalysts, and pollution-free emissions. However, the high operating temperature (800-1200℃) of the traditional SOFC can reduce the long-term stability and cause the difficulties in either the selecting of material or the sealing of SOFC. Therefore, great efforts have been devoted to developing the intermediate temperature SOFC (IT-SOFC), which works at 600-800℃. In the IT-SOFC, the ionic conductivity of doped CeO2-based electrolyte has a significant advantage relative to that of the conventional yttria-stabilized zirconia (YSZ) electrolyte. For example, at 600℃, the ionic conductivity of Sm-doped CeO2 is 0.02 S/cm much higher than that of the traditional YSZ electrolyte (only 0.0032 S/cm). Therefore, the doped CeO2-based electrolyte is a very promising electrolyte for IT-SOFC.Recently, the co-doping of two different elements into CeO2 has become a hot research topic. The ionic conductivity of Sm3+ and Sr2+ co-doped CeO2 has proved to be nearly twice as high as that of Sm3+ doped CeO2 (SDC). However, the mechanism for the co-doping effect on the conductivity of CeO2 is not clear. In this paper, Sm3+ and Sr2+ co-doped CeO2 is systematically studied using the DFT+U method. The microscopic properties of the Sm3+ and Sr2+ co-doped CeO2 including electronic density of states, band structure, oxygen vacancy formation energy and oxygen vacancy migration energy and so on have been calculated and analyzed by comparing with those of the Sm3+ or Sr2+ single doped CeO2. The calculation results indicate that Sm3+ and Sr2+ co-doping has a synergistic effect on the performance improvement of CeO2-based electrolyte, which can not only suppress the electronic conductivity of doped CeO2 system, but also can reduce the oxygen vacancy formation energy on the basis of single doped CeO2. The existence of Sm3+ can help to reduce the trapping effect of Sr2+ on oxygen vacancies, meanwhile the addition of Sr2+ can further reduce the minimum oxygen vacancy migration energy on the basis of SDC. Calculations by the climbing image nudged elastic band (CINEB) method indicate that the oxygen vacancy migration energy of the co-doped system can reach as low as 0.314/0.295 eV, which is lower than the minimum oxygen vacancy migration energy of SDC. Our research reveals the synergistic mechanism for Sm3+ and Sr2+ co-doping effect on the conductivity of CeO2, which is of great instructive significance for the further research and development of other high-performance co-doped electrolyte materials in IT-SOFC.

Ion Charge Dynamics in Ceria-Based Metal Insulator Metal Structure

This paper reports on the room temperature ambipolar diffusion of oxygen vacancies and electrons in epitaxial films of pure CeO2 and 20% Sm-doped CeO2 a few tens of nanometers thick. To this aim, we fabricated heteroepitaxial structures consisting of an epitaxial ceria film sandwiched between a Pt upper electrode and a conducting substrate of Nb-doped SrTiO3 (lower electrode). The observed decay of the electrical conductivity was investigated. In particular, following this approach, we could measure room temperature diffusion coefficient in thin monocrystalline dielectric layers. While pure ceria is interesting for memory device applications, in doped ceria the resistive switching involves diffusion mechanisms that occur on much longer time scales. Under this respect, doped ceria is particularly suitable to be used in artificial neuronal devices.

In-situ Transmission Electron Microscopy Study of Oxygen Vacancy Ordering and Dislocation Annihilation in Undoped and Sm-doped CeO2 Ceramics During Redox Processes

Ceria (CeO2) based ceramics have been widely used for many applications due to their unique ionic, electronic, and catalytic properties. Here, we report our findings in investigating into the redox processes of undoped and Sm-doped CeO2 ceramics stimulated by high-energy electron beam irradiation within a transmission electron microscope (TEM). The reduced structure with oxygen vacancy ordering has been identified as the CeO1.68 (C-Ce2O3+δ) phase via high-resolution TEM. The reduction of Ce4+ to Ce3+ has been monitored by electron energy-loss spectroscopy. The decreased electronic conductivity of the Sm-doped CeO2 (Sm0.2Ce0.8O1.9, SDC) is revealed by electron holography, as positive electrostatic charges accumulated at the surfaces of SDC grains under electron beam irradiation, but not at CeO2 grains. The formation of the reduced CeO1.68 domains corresponds to lattice expansion compared to the CeO2 matrix. Therefore, the growth of CeO1.68 nuclei builds up strain inside the matrix, causing annihilation of ...

Effect of Infiltrated Transition Metals in Ni/Sm-Doped CeO2 Cermets Anode in Direct NH3-Fueled SOFCs

Ammonia (NH3) has attracted much attention as a fuel for SOFCs. In the case of well-established Ni-based cermets anode, however, the cell performance is poor due to the low catalytic activity for NH3 reforming. In this respect, it is necessary to develop the highly active anode for realizing direct NH3-fueld SOFCs. Previously, we prepared Ni-M (M : Mo, Ta, W and Nb)/ Sm-doped CeO2(SDC) anodes by infiltration of metal solutions into pre-sintered Ni/SDC cermets and revealed the activity of them as an anode for direct NH3-fueled SOFCs at temperature of 700 to 900 °C [1-2]. From these studies, we have proposed that the synergetic effect of Ni and added metals, which weakly and strongly bind to N atom, enhances the activity of the anodes for NH3 oxidation(NH3 reforming, followed by hydrogen oxidation). In addition, it was found that the enhancement of the activity for NH3 oxidation strongly depended on the added metal. Among them, Mo was the most effective element as an additive. On the other hand, the obvious enhancement of the activity for NH3 oxidation was not observed when Nb, Ta and W were added, which have the larger metal-nitrogen (M-N) binding energy than Mo. The activity of the Ni-M binary anode seemed to be determined by the interaction potential between catalytic surface and N atom, produced by Ni and added metals. Here, we focus chromium(Cr) and vanadium(V) as an additive, because Cr and V have the moderate M-N binding energy (ranked in the order of Mo < Cr < V < W < Nb < Ta) among the metals used in our previous studies. The addition of Cr and V into the Ni/SDC cermets enhanced the activity of the anode for NH3 oxidation at temperature of 700 to 900 °C. The formation of Ni metal and nitrides (CrN and VN) was confirmed in each anode at 700 °C. This suggests that the synergetic effect of Ni and Cr(V), which has weekly and strongly bind to N atom enhances the activity of the anode for NH3 oxidation. Cr was more effective than Mo as an additive, but V was not. The relationship between the activity of the anode and the M-N binding energy of the added metal are discussed. Acknowledge This work was supported by “Kyoto Environmental Nanotechnology Cluster” and “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan. Reference [1] M. Hashinokuchi et al., Solid State Ionics, 285, (2016) 222 [2] R. Yokochi et al., ECS Trans. 68(2015) 2745.

A Simple Descriptor to Rapidly Screen CO Oxidation Activity on Rare-Earth Metal-Doped CeO2: From Experiment to First-Principles.

Ceria (CeO2) is an attractive catalyst because of its unique properties, such as facile redoxability and high stability. Thus, many researchers have examined a wide range of catalytic reactions on ceria nanoparticles (NPs). Among those contributions are the reports of the dopant-dependent catalytic activity of ceria. On the other hand, there have been few mechanistic studies of the effects of a range of dopants on the chemical reactivity of ceria NPs. In this study, we examined the catalytic activities of pure and Pr, Nd, and Sm-doped CeO2 (PDC, NDC, and SDC, respectively) NPs on carbon monoxide (CO) oxidation. Density functional theory (DFT) calculations were also performed to elucidate the reaction mechanism on rare-earth (RE)-doped CeO2(111). The experimental results showed that the catalytic activities of CO oxidation were in the order of CeO2 > PDC > NDC > SDC. This is consistent with the DFT results, where the reaction is explained by the Mars-van Krevelen mechanism. On the basis of the theoretical interpretation of the experimental results, the ionic radius of the RE dopant can be used as a simple descriptor to predict the energy barrier at the rate-determining step, thereby predicting the entire reaction activity. Using the descriptor, a wide range of RE dopants on CeO2(111) were screened for CO oxidation. These results provide useful insights to unravel the CO oxidation activity on various oxide catalysts.

Mechanism of Enhanced Sulfur Tolerance on Sm-Doped CeO2: A Density Functional Study

In this presentation, using first-principles calculation, the function of samarium (Sm) 4f states and Sm-perturbed O 2p states in enhancing the sulfur tolerance of Sm-doped CeO2 was elucidated. We find that the sulfur tolerance of Sm-doped CeO2 is closely related to the modification of O 2p states by the strong interaction between Sm 4f and O 2p states. In particular, the availability of unoccupied O 2p states near the Fermi level is responsible for enhancing the sulfur tolerance of Sm-doped CeO2 compared to the pure CeO2[1]. To better understand the importance of unoccupied O 2p states, the effect of various 4f shell dopants (Pr, Pm, and Eu) on the activity of surface lattice oxygen are also investigated. This work also hints on the importance of properly engineering the activity of oxygen ion in CeO2-based materials by adding dopant in order to develop sulfur-tolerant solid oxide fuel cell anode. [1] DH Lim, HS Kim, SP Yoon, J Han, CW Yoon, SH Choi, SW Nam, and HC Ham, Physical Chemistry Chemical Physics 16 (22), 10727-10733, (2014)

In-situ transmission electron microscopy study of oxygen vacancy ordering and dislocation annihilation in undoped and Sm-doped CeO2 ceramics during redox processes

Ceria (CeO2) based ceramics have been widely used for many applications due to their unique ionic, electronic, and catalytic properties. Here, we report our findings in investigating into the redox processes of undoped and Sm-doped CeO2 ceramics stimulated by high-energy electron beam irradiation within a transmission electron microscope (TEM). The reduced structure with oxygen vacancy ordering has been identified as the CeO1.68 (C-Ce2O3+δ) phase via high-resolution TEM. The reduction of Ce4+ to Ce3+ has been monitored by electron energy-loss spectroscopy. The decreased electronic conductivity of the Sm-doped CeO2 (Sm0.2Ce0.8O1.9, SDC) is revealed by electron holography, as positive electrostatic charges accumulated at the surfaces of SDC grains under electron beam irradiation, but not at CeO2 grains. The formation of the reduced CeO1.68 domains corresponds to lattice expansion compared to the CeO2 matrix. Therefore, the growth of CeO1.68 nuclei builds up strain inside the matrix, causing annihilation of dislocations inside the grains. By using in-situ high-resolution TEM and a fast OneView camera recording system, we investigated dislocation motion inside both CeO2 and SDC grains under electron beam irradiation. The dislocations prefer to dissociate into Shockley partials bounded by stacking faults. Then, the partials can easily glide in the {111} planes to reach the grain surfaces. Even the Lomer-Cottrell lock can be swept away by the phase change induced strain field. Our results revealed the high mobility of dislocations inside CeO2 and SDC grains during their respective redox processes.

Self-assembled oxide films with tailored nanoscale ionic and electronic channels for controlled resistive switching.

Resistive switches are non-volatile memory cells based on nano-ionic redox processes that offer energy efficient device architectures and open pathways to neuromorphics and cognitive computing. However, channel formation typically requires an irreversible, not well controlled electroforming process, giving difficulty to independently control ionic and electronic properties. The device performance is also limited by the incomplete understanding of the underlying mechanisms. Here, we report a novel memristive model material system based on self-assembled Sm-doped CeO2 and SrTiO3 films that allow the separate tailoring of nanoscale ionic and electronic channels at high density (∼1012 inch−2). We systematically show that these devices allow precise engineering of the resistance states, thus enabling large on–off ratios and high reproducibility. The tunable structure presents an ideal platform to explore ionic and electronic mechanisms and we expect a wide potential impact also on other nascent technologies, ranging from ionic gating to micro-solid oxide fuel cells and neuromorphics.

Effect of starting solution concentration in spray pyrolysis on powder properties and electrochemical electrode performance

Nano-composite powders consisting of Sr-doped SmCoO3 (SSC) and Sm-doped CeO2 (SDC) were synthesized by spray pyrolysis using different cation concentration solutions, and the effect of this cation concentration on the electrochemical performance of electrodes fabricated using the powders was investigated. Regardless of the cation concentration, spherical particles consisting of nano-order fine SSC and SDC crystallites were successfully obtained. Although the crystal size of all the synthesized powders was almost the same, the particle size increased with increasing cation concentration. The microstructure of the cathodes fabricated using the nano-composite powders clearly depended on the particle size of the starting powders; the microstructure became coarser with increasing particle size and the original particle shapes partially remained in the cathode network. Also, electrochemical measurements for solid oxide fuel cells with these cathodes revealed that the electrode performance was related to the microstructure. The electrode polarization resistance decreased with decreasing particle size, and a relatively fine microstructure cathode exhibited lower electrode polarization resistance, resulting in a high performance of 1.52Wcm−2 at 700°C. These results indicate that controlling the particle size, as well as controlling the nanostructure within the particles, is crucial to attain high performance electrodes.

Synthesis and properties of 1D Sm-doped CeO2 composite nanofibers fabricated using a coupled electrospinning and sol–gel methodology

Ce1−xSmxO2(x=0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol–gel with electrospinning and using poly-vinyl pyrrolidone (PVP) as the polymer medium, in an ethanol/water mixture. Control over the fabrication conditions was achieved through analysis of the most key synthetic factors, which include: (i) the applied field strength; (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. The optimum microstructural fiber morphology (high quality beeds-free fibers) was achieved using the following electrospinning parameters: an applied voltage of 18.5kV, a 7ml/h of solution feed rate and a 12% (w/w) of PVP composition. Morphological features of the resulting fibers were examined by scanning electron microscopy (SEM). The average fiber diameter was typically found to be in the range of 200–1100nm and 50–300nm, before and after calcination at 500°C, respectively. X-ray diffraction (XRD) results showed that the fluorite cubic structure was preserved for the entire Ce1−xSmxO2 compositional range studied, while elemental analysis using EELS and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the bulk and surface composition of the fibers. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) proved that the NFs are highly crystalline. The thermal stability of the composite (polymer/inorganic nitrate salts) NFs was further investigated in an inert atmosphere (N2) using thermogravimetric analysis (TGA), which allowed the transformation process of the NFs from composite to oxide to be monitored. The reducibility of the metal oxide NFs (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation–reduction cycles was evaluated using temperature-programmed reduction in a H2 atmosphere (H2-TPR). Acidic–basic features of the NFs and powder surfaces were studied through temperature programmed desorption (TPD) using NH3 and CO2 as probe molecules, where weak, medium and strong acid sites were successfully traced with profound differences depending on the morphology. The NFs' potential performance towards NH3 oxidation was also evaluated. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the NFs, as probed by CO2 adsorption. Pyridine adsorption followed by infrared spectroscopy (Py-FT-IR) studies unveiled the more profound Lewis acid presence in Ce0.5Sm0.5O2 NFs compared to bulk powder Ce0.5Sm0.5O2.

Characterization of Sm-doped CeO2 nanoparticles and their magnetic properties

Cubic phase Sm-doped CeO2 nanoparticles (Ce1−xSmxO2, x=0, 0.05, 0.10, 0.15 and 0.20) were synthesized by the polymer pyrolysis method. X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) were employed to characterize the phase, morphology, valence states and magnetic properties of the samples. The samples were calcined at the low temperature of 600°C which resulted in crystallite sizes of 10–20nm. Raman and XPS spectra showed the presence of Ce4+, Ce3+ and Sm3+ ions and oxygen vacancies in the samples. Magnetization curves obtained from all samples exhibited ferromagnetic behavior at room temperature (RT-FM) with a maximum value of 0.012emu/g for x=0.15. The data exhibited a good fit to bound magnetic polaron (BMP) model curves which account for the RT-FM behaviour by having sufficient concentrations of electrons bound to oxygen vacancies to facilitate a long-range exchange interaction between Ce3+ ions. However, the relatively low values obtained for the BMP concentrations suggest that other mechanisms may also be at play.

Robust nano-architectured composite thin films for a low-temperature solid oxide fuel cell cathode

Nano-precipitates of Sm-doped CeO2 were uniformly coated onto porous Pt thin films via cathodic electrochemical deposition. Deposition of only 5 min created an oxide coating that increased the values of the electrode conductance by more than two orders of magnitude and provided outstanding thermal stability even at 600 °C for more than 100 h compared to the bare Pt electrodes.

High power density cell using nanostructured Sr-doped SmCoO3 and Sm-doped CeO2 composite powder synthesized by spray pyrolysis

High power density solid oxide electrochemical cells were developed using nanostructure-controlled composite powder consisting of Sr-doped SmCoO3 (SSC) and Sm-doped CeO2 (SDC) for electrode material. The SSC-SDC nano-composite powder, which was synthesized by spray pyrolysis, had a narrow particle size distribution (D10, D50, and D90 of 0.59, 0.71, and 0.94 μm, respectively), and individual particles were spherical, composing of nano-size SSC and SDC fragments (approximately 10–15 nm). The application of the powder to a cathode for an anode-supported solid oxide fuel cell (SOFC) realized extremely fine cathode microstructure and excellent cell performance. The anode-supported SOFC with the SSC-SDC cathode achieved maximum power density of 3.65, 2.44, 1.43, and 0.76 W cm−2 at 800, 750, 700, and 650 °C, respectively, using humidified H2 as fuel and air as oxidant. This result could be explained by the extended electrochemically active region in the cathode induced by controlling the structure of the starting powder at the nano-order level.

Strongly enhanced oxygen ion transport through samarium-doped CeO2 nanopillars in nanocomposite films.

Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO2 embedded in supporting matrices of SrTiO3. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO2 films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO2 nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness.

Ionic Conductivity Increased by Two Orders of Magnitude in Micrometer-Thick Vertical Yttria-Stabilized ZrO2 Nanocomposite Films.

We design and create a unique cell geometry of templated micrometer-thick epitaxial nanocomposite films which contain ~20 nm diameter yttria-stabilized ZrO2 (YSZ) nanocolumns, strain coupled to a SrTiO3 matrix. The ionic conductivity of these nanocolumns is enhanced by over 2 orders of magnitude compared to plain YSZ films. Concomitant with the higher ionic conduction is the finding that the YSZ nanocolumns in the films have much higher crystallinity and orientation, compared to plain YSZ films. Hence, "oxygen migration highways" are formed in the desired out-of-plane direction. This improved structure is shown to originate from the epitaxial coupling of the YSZ nanocolumns to the SrTiO3 film matrix and from nucleation of the YSZ nanocolumns on an intermediate nanocomposite base layer of highly aligned Sm-doped CeO2 nanocolumns within the SrTiO3 matrix. This intermediate layer reduces the lattice mismatch between the YSZ nanocolumns and the substrate. Vertical ionic conduction values as high as 10(-2) Ω(-1) cm(-1) were demonstrated at 360 °C (300 °C lower than plain YSZ films), showing the strong practical potential of these nanostructured films for use in much lower operation temperature ionic devices.

Effect of Water Adsorption on Conductivity in Epitaxial Sm0.1Ce0.9O2 -δ Thin Film for Micro Solid Oxide Fuel Cells Applications

The growing demand for miniaturized systems for energy conversion and storage has prompted extensive research aimed at fabricating electrochemical devices, such as solid oxide fuel cells for portable applications (μ-SOFCs). This goal requires reducing the operating temperature by producing components as thin films. Nowadays, there is a huge gap between macroscopic device-level electrochemical techniques and microscopic electrochemical techniques to study atomic-level diffusion and transport process. Recently, a new scanning probe microscopy technique, named electrochemical strain microscopy (ESM) has been developed in order to study the structure and physical properties on the microscopic level. After applying the dc bias to the tip, the oxygen vacancies and protons injection or annihilation can occur, depending on the working conditions and the material properties. The subsequent oxygen ion or proton movement results in localized strain under the tip, which can be detected through dynamic surface displacement.[1] This technique can be very useful to investigate the electrochemical activity at the nano-scale in ionic or proton conductors. In this presentation, I will discuss several examples of high-resolution studies of pure and Sm-doped CeO2 epitaxial thin films surfaces which allowed to understand water interaction and conductivity mechanisms on the nanoscale. In particular I will show: (1) The effect of the different doping concentrations on Sm1-xCexO2-a in terms of different transport mechanism and different type of charge carriers [2]. (2) The role of granularity and porosity on the oxygen ion or proton conduction 20% Sm doped CeO2 nanocrystalline films [3]. (3) The bias dependent mechanisms of irreversible cathodic and anodic processes on a pure CeO2 film.[4] [1] A. Kumar et al. Nature Chemistry, 2011, 3,707. [2] Nan Yang et al. ACS Nano DOI: 10.1021/nn505345c (2014) [3] S. Doria, Nan Yang, et al. Appl. Phys. Lett. 103, 171605 (2013) [4] Nan Yang et al. Nanotechnology 25, 075701 (2014).

Application of spray deposition techniques for fabrication of Sm-doped CeO2 thin films on biaxially textured Ni-W substrate

Chemical and thermo-resistant buffer layers are commonly used to separate metal substrates and high-temperature superconductors (HTS). This ensures that no reaction occurs between the superconductor's precursor materials and the substrate metal during high-temperature HTS tape processing. Various materials and coating procedures are available, with each combination of buffer layers requiring specific characteristics. This paper reports a feasibility study into the development and use of simple, aerosol-based production methods of samarium-doped cerium thin films for subsequent use as a buffer layer between a Ni substrate and yttrium barium copper oxide (YBCO) superconductor. The suggested methods are very cost effective and hence attractive for commercial use. It was shown that different types of aerosol nebulisers can produce textured, pinhole-free films of high integrity and uniformity. Thickness of the films could be precisely controlled by the deposition time enabling achieving any required value starting from 40nm. It was found that that the optimum film thickness is between 120 and 180nm, and higher film thickness led to the surface cracking. Microstructural and crystallographic characteristics, and chemical composition of fabricated films are also reported and discussed.

Electronic structure and oxygen ion conductivity of as-deposited Ce0.90Sm0.10O2−δ thin film prepared by RF magnetron sputtering

The physical properties and electronic structure of Sm-doped CeO2 (Ce0.90Sm0.10O2−δ) in the thin-film form have been studied. The as-deposited thin film exhibits (111) orientation on an Al2O3(0001) substrate. The lattice constant of the thin film is larger than that of the bulk crystal. The Ce0.90Sm0.10O2−δ thin film has the mixed valence states of Ce4+ and Ce3+. The electrical conductivity of Ce0.90Sm0.10O2−δ thin film in the temperature region from 200 to 700 °C is higher than that of the undoped CeO2 thin film and is independent of the oxygen partial pressure, indicating the occurrence of high oxygen-ion conduction. The valence band consists of the O 2p state hybridized with the Ce 4f state. The 40% Ce3+ (4f1L) state in Ce0.90Sm0.10O2−δ thin film, which was estimated from the resonant photoemission spectra, contributes to the high oxygen-ion conduction and low activation energy.

Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO3 and SrTiO3 grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO2 and 8 mol% Y2O3 stabilized ZrO2 are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.

Preparation and performance of solid oxide fuel cells with YSZ/SDC bilayer electrolyte

YSZ (Y2O3-stabilized ZrO2)/SDC (Sm-doped CeO2) bilayer electrolyte film was successfully fabricated on NiO/YSZ anode substrate using stepwise sintering processing by screen-printing technique. OCVs (open-circuit voltages) of 1.06V, 1.05V and 0.88V were achieved at 750°C for single cells with bilayer electrolyte of 12μm-SDC/8μm-YSZ, 12μm-SDC/5μm-YSZ, and 12μm-SDC/2μm-YSZ, respectively. Interdiffusion of ions at YSZ/SDC interface and formation of YSZ–SDC solid solution after sintering at 1400°C for 2h was investigated. The EDX result suggested that the region for the interdiffusion in a YSZ/SDC bilayer structure was 2.0μm from the YSZ/SDC interface into the YSZ layer for Sm and Ce, and 0.5μm into the SDC layer for Zr and Y. The YSZ–SDC solid solution exhibited a low electrical conductivity, which negatively affected the performance of single cell. After two thermal cycles, the maximum power density of the single cell exhibited a significant decrease. The destruction of YSZ/SDC bilayer electrolyte structure was not observed during the thermal cycles.