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In this study, the structural and electrochemical properties of commercial powders of the nominal compositions Ce0.8Gd0.2O1.9, Sc0.1Ce0.01Zr0.89O1.95, and Sc0.09Yb0.01Zr0.9O1.95 were investigated. The materials are prospective candidates to be used in electrochemical devices, i.e., gas sensors and fuel cells. Based on a comparison of the EIS spectra in different atmospheres (synthetic air, 3000 ppm NH3 in argon, 10% H2 in argon), the reactions on the three-phase boundaries were proposed, as well as the conduction mechanisms of the electrolytes were described. The Ce0.8Gd0.2O1.9 material is a mixed ionic–electronic conductor, which makes it suitable for anode material in fuel cells. Moreover, it exhibits an apparent and reversible response for ammonia, indicating the possibility of usage as an NH3 gas-sensing element. In zirconia-based materials, electrical conduction is realized by oxygen ion carriers. Among them, the most promising from an applicative point of view seems to be Sc0.09Yb0.01Zr0.9O1.95, showing a high, reversible reaction with hydrogen. [ABSTRACT FROM AUTHOR]

CO2 conversion into fuels and high value-added chemical feedstocks, such as methane, has gained novel interest as a crucial process for further manufacturing multi-carbon products. Methane, CH4, becomes a promising alternative for environmental and energy supply issues. Nickel-based catalysts were found to be very active and selective for CH4 production. The use of promoter and support material to develop high activity, high selectivity, and durable catalysts for CO2 methanation at low temperature is a challenge. Gadolinium-Doped Ceria (GDC) has been known as material for Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolysis Cell (SOEC) due to higher ionic conductivity and lower operating temperatures. However, few researches have been done regarding to CO2 methanation over GDC as catalyst support so far. In this present work, CO2 methanation was investigated over bimetallic Ni-Fe catalyst supported by GDC. The results showed that CH4 production rate by using Ni-Fe/GDC catalyst was higher than that of GDC at all reaction temperatures carried on. Ni-Fe/GDC showed remarkable CH4 production rate as of 17.73 mmol.gcat−1.h−1 at 280 °C. No catalytic activity was produced by GDC catalyst only. The highest CO2 conversion (46.50%) was observed at 280 °C, with almost 100% selectivity to CH4. The turnover frequency (TOF) value of Ni-Fe/GDC (4529.32 h−1) was the highest than that of Ni and common CO2 methanation catalyst, Ni/Al2O3 catalysts at 280 °C, further displaying the outstanding low-temperature catalytic activity. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

CO2 conversion into fuels and high value-added chemical feedstocks, such as methane, has gained novel interest as a crucial process for further manufacturing multi-carbon products. Methane, CH4, becomes a promising alternative for environmental and energy supply issues. Nickel-based catalysts were found to be very active and selective for CH4 production. The use of promoter and support material to develop high activity, high selectivity, and durable catalysts for CO2 methanation at low temperature is a challenge. Gadolinium-Doped Ceria (GDC) has been known as material for Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolysis Cell (SOEC) due to higher ionic conductivity and lower operating temperatures. However, few researches have been done regarding to CO2 methanation over GDC as catalyst support so far. In this present work, CO2 methanation was investigated over bimetallic Ni-Fe catalyst supported by GDC. The results showed that CH4 production rate by using Ni-Fe/GDC catalyst was higher than that of GDC at all reaction temperatures carried on. Ni-Fe/GDC showed remarkable CH4 production rate as of 17.73 mmol.gcat-1.h-1 at 280 °C. No catalytic activity was produced by GDC catalyst only. The highest CO2 conversion (46.50%) was observed at 280 °C, with almost 100% selectivity to CH4. The turnover frequency (TOF) value of Ni-Fe/GDC (4529.32 h-1) was the highest than that of Ni and common CO2 methanation catalyst, Ni/Al2O3 catalysts at 280 °C, further displaying the outstanding low-temperature catalytic activity. [ABSTRACT FROM AUTHOR]

Gadolinium-doped ceria (GDC) interlayers are required to prevent the interfacial reaction between La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode and Y2O3-stabilized ZrO2 (YSZ) electrolyte in solid oxide fuel cells (SOFCs). However, it's difficult to prepare a thin and dense GDC interlayer on the sintered half-cell at a low temperature. In this study, the physical vapor deposition (PVD) method was employed to successfully manufacture dense GDC interlayers with the thickness of 1 μm. The influences of GDC sintering temperature (900 °C, 1000 °C and 1100 °C) on cell performance characteristics and degradation behavior were investigated. The cell with GDC interlayer sintered at 1100 °C showed the lowest degradation rate during the 216-h operation. The best stability was attributed to the most effective inhibition of Sr diffusion by the GDC interlayer, which was demonstrated by the almost unchanged Ohmic and polarization resistances during the aging stage and the negligible Sr enrichment at YSZ/GDC interface. Compared to the conventional screen-printed GDC interlayers (sintered above 1250 °C), the GDC interlayer prepared by the PVD method and sintered at 1100 °C was significantly denser and thinner, showing a promising application prospect due to its benefits for cell stability.

The effects of precursor powder uniformity on structure and electrical properties of Gd-doped CeO2 (GDC) electrolytes were studied. The as-synthesized GDCx powders (x = 5, 10 and 15 at.%) were calcined at 600 and 1200°C and combined in mass ratios of 100:0 and 95:5 to obtain two precursor powders with different particle size distributions. Sintering of the pressed pellets was performed at 1300 and 1400°C for 10 h. Crystal structure, microstructure and electrical properties of the samples were investigated by X-ray diffraction, scanning electron microscopy and AC impedance spectroscopy, respectively. When a smaller proportion of large particles (calcined at 1200 °C) were present in the precursor powders, sinterability of the prepared samples is slowed down, which had an adverse effect on electrical conductivity. The lower the concentration of Gd, the more significant is the adverse effect. At higher sintering temperature (1400°C), the influence of Gd concentration on microstructure and ionic conductivity is more obvious. The GDC15 sample, prepared from the precursor powder calcined at 600°C, had the highest conductivity and σasGB/σBulk ratio at 300°C.

The paper focuses on the synthesis of gadolinium-doped ceria (CexGd1 – xO2 – y) thin films on the anodes of solid oxide fuel cells by reactive dual magnetron sputtering. CexGd1 – xO2 – y thin films 4 μm thick are deposited in the transition and oxide modes, differing by the oxygen concentration in the vacuum chamber. Residual stresses after the film deposition and thermal annealing in air are determined by the curvature of the anode plates. Dependences are obtained between the deposition modes, residual stresses and parameters of fuel cells with the CexGd1 – xO2 – y electrolyte. The surface morphology and cross-section of the films are studied on a scanning electron microscope. The X-ray diffraction analysis is additionally conducted to study the structure of gadolinium-doped ceria thin films using the synchrotron radiation during 1300°С annealing. It is shown that under certain conditions of the film deposition and annealing, compressive stresses can transfer to tensile stresses, which reduces the anode plate deformation after the CexGd1 – xO2 – y electrolyte deposition. [ABSTRACT FROM AUTHOR]

Gadolinium-doped ceria (GDC) nanopowders, prepared using the co-precipitation synthesis method, were applied as a starting material to form ceria-based thin films using the electron-beam technique. The scanning electron microscopy (SEM)analysis of the pressed ceramic pellets' cross-sectional views showed a dense structure with no visible defects, pores, or cracks. The AC impedance spectroscopy showed an increase in the total ionic conductivity of the ceramic pellets with an increase in the concentration of Gd2O3 in GDC. The highest total ionic conductivity was obtained for Gd0.1Ce0.9O2-δ (σtotal is 11 × 10−3 S∙cm−1 at 600 °C), with activation energies of 0.85 and 0.67 eV in both the low- and high-temperature ranges, respectively. The results of the X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectrometer (ICP-OES) measurements revealed that the stoichiometry for the evaporated thin films differs, on average, by ~28% compared to the target material. The heat-treatment of the GDC thin films at 600 °C, 700 °C, 800 °C, and 900 °C for 1 h in the air had a minor effect on the surface roughness and the morphology. The results of Raman spectroscopy confirmed the improvement of the crystallinity for the corresponding thin films. The optimum heat-treating temperature for thin films does not exceed 800 °C. [ABSTRACT FROM AUTHOR]

Ceria (CeO2) and its solid solutions with Gd2O3 are technologically important and environmentally friendly materials with numerous interesting properties and important applications. Nevertheless, the magnetic properties of ceria are even today not fully understood, and magnetoelastic coupling in pure or doped ceria remains essentially unexplored. This has been so, in part, due to the difficulty of measuring very small magnetostrictive strains in weakly paramagnetic materials. During the last decade, however, technical advances have enabled sensitive and accurate measurements of sample deformation in high magnetic fields. Here, forced magnetostriction (MS) in Gd2O3‐CeO2 solid solution ceramics (Ce1−xGdxO2−x/2, 0 ≤x≤ 1) at room temperature is characterized. In a pulsed magnetic field μ0H≤ 60 Tesla, longitudinal MS strain is observed to depend on the square of the field amplitude and to increase linearly with Gd3+ concentration but is not sensitive to the lattice symmetry of the ceramics. The theory attributes the origin of the observed strain to the single‐ion MS response of Gd3+ to the crystal field via mixing of ground and excited electronic states and covalent hybridization with oxygen ligands. Contributions of charge‐compensating oxygen vacancies and/or Van Vleck paramagnetism to the observed magnetoelastic coupling are determined to be negligible. [ABSTRACT FROM AUTHOR]

Flash sintering was discovered in 2010, where a dog‐bone‐shaped zirconia sample was sintered at a furnace temperature of 850°C in <5 s by applying electric fields of ~100 V cm−1 directly to the specimen. Since its discovery, it has been successfully applied to several if not all oxides and even ceramics of complex compositions. Among several processing parameters in flash sintering, the electrical parameters, i.e., electric field and electric current, were found to influence the onset temperature for flash and the degree of densification respectively. In this work, we have systematically investigated the influence of the electrical parameters on the onset temperature, densification behavior, and microstructure of the flash sintered samples. In particular, we focus on the development of a processing map that delineates the safe and fail regions for flash sintering over a wide range of applied current densities and electric fields. As a proof of concept, gadolinium‐doped ceria (GDC) is shown as an example for developing of such a processing map for flash sintering, which can also be transferred to different materials systems. Localization of current coupled with hot spot formation and crack formation is identified as two distinct failure modes in flash sintering. The grain size distribution across the current localized and nominal regions of the specimen was analyzed. The specimens show exaggerated grain growth near the positive electrode (anode). The region adjacent to the negative electrodes (cathode) showed retarded densification with large concentration of isolated pores. The electrical conductivity of the flash sintered and conventional sintered samples shows identical electrical conductivity. This quantitative analysis indicates that similar sintering quality of the GDC can be achieved by flash sintering at temperature as low as 680°C. [ABSTRACT FROM AUTHOR]

Mixed ionic-electronic conducting materials are not used as a single-layer electrolyte of solid oxide fuel cells (SOFCs) at relatively high operating temperatures of ~800 °C. This is because of a significant decrease in the open-circuit voltage (OCV) and, consequently, the SOFC power density. The paper presents a comparative analysis of the anode-supported SOFC properties obtained within the temperature range of 600 to 800 °C with yttria-stabilized zirconia (YSZ) electrolyte and gadolinium-doped ceria (GDC) electrolyte thin films. Electrolyte layers that are 3 µm thick are obtained by magnetron sputtering. It is shown that at 800 °C, the SOFC with the GDC electrolyte thin film provides an OCV over 0.9 V and power density of 2 W/cm2. The latter is comparable to the power density of SOFCs with the YSZ electrolyte, which is a purely ionic conductor. The GDC electrolyte manifests the high performance, despite the SOFC power density loss induced by electronic conductivity of the former, which, in turn, is compensated by its other positive properties.

Electrolyte powders with low sintering temperature and high-ionic conductivity can considerably facilitate the fabrication and performance of solid oxide fuel cells (SOFCs). Gadolinia-doped ceria (GDC) is a promising electrolyte for developing intermediate- and low-temperature (IT and LT) SOFCs. However, the conventional sintering temperature for GDC is usually above 1200 °C unless additives are used. In this work, a nanocrystalline powder of GDC, (10 mol% Gd dopant, Gd 0.1 Ce 0. 9 O 1.95) with low-sintering temperature has been synthesized using ammonium benzoate as a novel, environmentally friendly and cost-effective precursor/precipitant. The synthesized benzoate powders (termed washed- and non-washed samples) were calcined at a relatively low temperature of 500 °C for 6 h. Physicochemical characteristics were determined using thermal analysis (TG/DTA), Raman spectroscopy, FT-IR, SEM/EDX, XRD, nitrogen absorptiometry, and dilatometry. Dilatometry showed that the newly synthesized GDC samples (washed and non-washed routes) start to shrink at temperatures of 500 and 600 °C (respectively), reaching their maximum sintering rate at 650 and 750 °C. Sintering of pelletized electrolyte substrates at the sintering onset temperature for commercial GDC powder (950 °C) for 6 h, showed densification of washed- and non-washed samples, obtaining 97.48 and 98.43% respectively, relative to theoretical density. The electrochemical impedance spectroscopy (EIS) analysis for the electrolyte pellets sintered at 950 °C showed a total electrical conductivity of 3.83 × 10−2 and 5.90 × 10−2 S cm−1 (under air atmosphere at 750 °C) for washed- and non-washed samples, respectively. This is the first report of a GDC synthesis, where a considerable improvement in sinterability and electrical conductivity of the product GDC is observed at 950 °C without additives addition. [ABSTRACT FROM AUTHOR]

In the present work, 1 mol% alkali metals (Li, Na, K) doped Ce 0.9 Gd 0.1 O 2-δ (GDC) electrolytes are prepared by citrate-nitrate sol-gel autoignition process. The effects of monovalent alkali metals on the phase structure, micromorphology and grain boundary conductivity of GDC electrolyte are investigated. All Ce 0.89 Gd 0.1 A 0.01 O 2-δ (AGDC, A = Li, Na, K) ceramics exhibit a complete fluorite-type structure. SEM results show that all samples sintered at 1400 °C for 5 h have been achieved high densification, and the addition of alkali metals is conducive to the growth of grains. The space charge potential calculated by impedance data has decreased obviously after alkali metals are incorporated into GDC and the value of Ce 0.89 Gd 0.1 K 0.01 O 2-δ ceramic is apparently reduced from 0.063 V (GDC) to 0.033 V at 400 °C. These results indicate monovalent alkali metals are beneficial to improve grain boundary conductivity and even total electrical conductivity. Additionally, among all the samples, the Ce 0.89 Gd 0.1 K 0.01 O 2-δ electrolyte shows the highest total ionic conductivity of 2.64 × 10−2 S/cm at 700 °C in dry air. The single cell with Ce 0.89 Gd 0.1 K 0.01 O 2-δ electrolyte promises the best power density of 624.5 mW cm−2 at working temperature of 700 °C. Therefore, the monovalent alkali metals dopants have promoting effects on improving the grain boundary conductivity, enhancing the sintering activity and output performance of GDC as an electrolyte for IT-SOFCs. [ABSTRACT FROM AUTHOR]

This study aims to understand the effect of the electrical field on microstructure evolution during field‐assisted sintering or spark plasma sintering (FAST/SPS) of 10 mol% gadolinium‐doped ceria (GDC) with experimental and numerical methods. The novelty of this study has been the observation of enhanced grain growth in the region closer to the anode, even under FAST/SPS conditions with electrical fields less than 5 V/cm. The grain growth kinetics, including determination of activation energy and grain‐boundary mobility, were analyzed along the cross section of the samples for different temperatures and dwell periods. With an increase in distance from the anode, reduction in the activation energy for grain growth and grain‐boundary mobility was observed. These observations attributed to the attraction of oxygen ions to the anode region under an electrical field with an increase in defects along the grain boundaries. Thereby an increase in the grain‐boundary mobility and larger grains in that region were observed. A homogenous microstructure was observed in a case where the current did not flow through the sample. Furthermore, a numerical strategy has also been developed to simulate this behavior in addition to heat generation, heat transfer, and densification using Finite Element Methods (FEM) simulations. The simulation results provided an insight into the presence of a potential difference across the cross section of the samples. The simulation results were also in good agreement with the experimental observations. [ABSTRACT FROM AUTHOR]

A dense Ce0.9Gd0.1O2−d (GDC) interlayer is an essential component of the SOFCs to inhibit interfacial elemental diffusion between zirconia‐based electrolytes (eg YSZ) and cathodes. However, the characteristic high sintering temperature of GDC (>1400°C) makes it challenging to fabricate an effective highly dense interlayer owing to the formation of more resistive (Zr,Ce)O2 interfacial solid solutions with YSZ at those temperatures. To fabricate a useful GDC interlayer, we studied the influence of transition metal (TM) (Co, Cu, Fe, Mn, & Zn) doping on the sintering and electrochemical properties of GDC. Dilatometry data showed dramatic drops in the necking and final sintering temperatures for the TM‐doped GDCs, improving the densification of the GDC in the order of Fe > Co > Mn > Cu > Zn. However, the electrochemical impedance data showed that among various transition metal dopants, Mn doping resulted in the best electrochemical properties. Anode supported SOFCs with Mn‐doped, nano, and commercial‐micron GDC interlayers were compared with regard to their performance and stability levels. Although all of the SOFCs showed stable performance, the SOFC with the Mn‐doped GDC interlayer showed the highest power density of 1.14 W cm−2 at 750°C. Hence, Mn‐doped GDC is suggested for application as an effective diffusion barrier layer in SOFCs. [ABSTRACT FROM AUTHOR]

This paper deals with the development and potential application of a novel mixed ionic-electronic conductive anode composite comprised of copper and iron oxide based on gadolinium-doped ceria (CuO–Fe 2 O 3 /GDC) for solid-oxide fuel cell (SOFC). Synthesis of the nanocrystalline CuO–Fe 2 O 3 /GDC powders was carried out using a novel co-precipitation method based on ammonium tartrate as the precipitant in a mixed-cationic solution composed of Cu2+, Fe3+, Gd3+, and Ce3+. Thermal decomposition of the resultant precipitate after drying (at 55 °C) was investigated in a wide range of temperature (25–900 °C) using simultaneous DSC/TGA technique in air. The DSC/TGA results suggested the optimal calcination temperature of 500 °C for obtaining the nanocrystalline anode composite from the resultant precipitate. The synthesised CuO–Fe 2 O 3 /GDC samples were further characterised using XRD, dilatometry, FESEM, and EDX. Several single cells of SOFCs were fabricated in the anode-supported geometry using the synthesised CuO–Fe 2 O 3 /GDC composite as the anode, GDC/CuO composite as the electrolyte, and LSCF/GDC composite as the cathode layer. The fabricated cells were analysed using FESEM imaging and EIS analysis, where an equivalent circuit containing five R-CPE terms was used to interpret the EIS data. The module fitted well the impedance data and allowed for a detailed deconvolution of the total impedance spectra. The catalytic activity and uniformity of the synthesised nanocomposites was further evaluated using TPR analysis, demonstrating excellent activity at temperatures as low as 200 °C. [ABSTRACT FROM AUTHOR]

The effects of powder characteristics and conformation methods on green microstructure have been investigated, and microstructural evolution was analyzed based on the green density and the different sintering techniques. Colloidal processing of nanopowders with narrow particle size distribution (15 ± 5 nm) can be more problematic than dry processing and can lead to more heterogeneous microstructures. Two-step sintering can be used to obtain dense nanostructured samples with more flexibility than microwave sintering and still at lower temperatures than conventional sintering. The sinterability of Ce 0.8 Gd 0.2 O 1.9 is significantly improved by Zn addition, which can reduce sintering temperature to values as low as 800, 1150 and 1200 °C for two-step, microwave and conventional sintering, respectively, in order to achieve relative densities above 90%. Microscopic grain boundary conductivity is shown to be improved in nanostructured samples, despite the higher grain boundary density. [ABSTRACT FROM AUTHOR]

In current-rate flash-sintering experiments the current is injected into the specimen from the very start and then increased at a constant rate, while the furnace is held at a constant temperature. The power supply remains under current control. The flash is induced at low current densities which reduces local heating at the electrodes. It leads to a uniform grain size across the entire gage length of the dog-bone specimen. This work pertains to 10 mol.% gadolinium-doped ceria flash sintered at current-rates ranging from 50 mA min−1 to 1000 mA min−1 at a furnace temperature of 680 °C. Full densities are obtained at a current density limit of 200 mA mm–2. Densification is shown to depend only on the instantaneous value of the current density, and not on the current-rate. The grain size, however, is shown to become finer at higher current-rates. A preliminary analysis of the "energy deficit", that is, the estimated power input corresponding to the temperature as measured with a pyrometer, and the actual power consumption, estimates that huge concentrations of Frenkel defects may be introduced in the flash process. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this paper, we discuss the progression of flash sintering in 10mol% gadolinium-doped ceria specimens. Flash transition is correlated with the generation of n-type electronic conductivity in air under direct-current bias. Its origin is attributed to partial reduction of the material which propagates from the cathodic-to-anodic region. The phenomenon was observed, in-situ , by monitoring the development of electrochemical blackening during the incubation period of the flash-experiment. Anomalous features, including shift in the valence band edge, shrinkage of the band-gap and change in the oxidation state of Ce in flashed samples was confirmed by X-ray photoelectron spectroscopy and diffuse reflectance measurements. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Fabrication of nanoporous doped ceria thin film by sputtering method has attracted attention for lowering operating temperature of solid oxide fuel cells and enhancing active sites for oxygen reduction reaction (ORR). However, it is difficult to obtain nanoporous structure of doped ceria by sputtering due to deposition characteristic of oxide thin film. A novel method for fabricating 300nm-thickness of nanoporous gadolinium-doped ceria (GDC) interlayer is developed by combining wet-chemical etching and co-sputtering. The nanostructure of thin film Ag-GDC cermet varied with deposition power of Ag and GDC was optimized for cathode interlayer. By etching Ag nanoparticle out of the Ag-GDC cermet interlayer, the highly porous nanostructure of GDC was obtained. The peak power density of the cell with nanoporous GDC interlayer was increased by more than a factor of 2.5 compared to that of the cell without the interlayer. Nanostructure and material properties of the GDC interlayer were analyzed by FESEM, XRD, and XPS. [ABSTRACT FROM AUTHOR]

Some oxygen defective metal oxides, such as cerium and bismuth oxides, have recently shown exceptional electrostrictive properties that are even superior to the best performing lead-based electrostrictors, e.g. lead-magnesium-niobates (PMN). Compared to piezoelectric ceramics, electromechanical mechanisms of such materials do not depend on crystalline symmetry but on the concentration of oxygen vacancy ( V O ⋅ ⋅ ) in the lattice. In this work, we investigate for the first time the role of oxygen defects configuration on the electro-chemo-mechanical properties. This is achieved by tuning the oxygen defects blocking barrier density in polycrystalline gadolinium doped ceria with known oxygen vacancy concentration, Ce 0.9 Gd 0.1 O 2-δ, δ = 0.05. Nanometric starting powders of ca. ∼12 nm are sintered in different conditions, including field assisted spark plasma sintering (SPS), fast firing and conventional method at high temperatures. These approaches allow controlling grain size and Gd-dopant diffusion, i.e. via thermally driven solute drag mechanism. By correlating the electro-chemo-mechanical properties, we show that oxygen vacancy distribution in the materials plays a key role in ceria electrostriction, overcoming the expected contributions from grain size and dopant concentration. Image 1 [ABSTRACT FROM AUTHOR]

Two different gadolinium-doped ceria ceramics are prepared from two different powders, one commercially available synthesised by solid state reaction and another produced by tartaric acid assisted sol-gel synthesis. The specimens have a different microstructure, while the XRD patterns of powders showed a pure cubic fluorite structure without any impurity phase. The electrical properties are studied at frequencies up to 10 GHz by combining broadband 2-electrode and 4-electrode impedance spectroscopy methods. Primary electrical measurements showed that the values of grain conductivity and its activation energies for both ceramics were nearly the same. However, due to different contributions of the grain boundary mediums, total conductivities and their activation energies are found to be considerably different. The advantage of the 4-electrode method allowed us to measure the pure electrical response of grain boundaries, bypassing any interferences caused by interfacial impedance. By using these data, the temperature behaviour of distribution of relaxation times in the grain boundary is studied. A broadening of this distribution with increasing temperature is found for both specimens, contrary to a previously observed phenomenon in the grain of oxygen ion conductive ceramics and single crystals. It is shown that, supposing individual relaxation times behave according to the Arrhenius law, both activation energy and pre-exponential factor must be distributed. [ABSTRACT FROM AUTHOR]

A novel method for bottom-up synthesis of two-dimensional (2D) gadolinium-doped cerium oxide (CGO) nanosheets is developed and demonstrated as an efficient precursor for interdiffusion barrier layer deposition in solid oxide fuel cells. The CGO is the standard material used as an interlayer in intermediate-temperature solid oxide fuel cells to avoid undesirable reactions between lanthanum strontium cobalt ferrite (LSCF) cathode and yttria-stabilized zirconia (YSZ) electrolyte materials. Herein, the shape-control of the 2D CGO by a low-cost wet-chemical method allowing for the fabrication of fully dense barrier layer of CGO is reported. The high surface coverage promoted by the 2D CGO nanosheets resulted in a thin (∼ 1 µm) and dense interdiffusion barrier layer sintered at 1150 °C preventing the undesirable reaction between oxide ion conducting phases occurring at higher temperatures. The electrochemical properties of solid oxide fuel cells confirmed the CGO nanosheet as an efficient layer for preventing the formation of resistive phases at the electrolyte/cathode interface. [Display omitted] • Innovative synthesis method for efficient 2D-layered gadolinium doped-ceria (CGO) electrolytes. • 2D CGO nanosheets, with high surface coverage, result in dense layer at mild sintering temperature. • CGO nanosheets prevent resistive phases and enhance solid oxide fuel cell performance. [ABSTRACT FROM AUTHOR]

Abstract In this work, cobalt and zinc-doped Ce0.8Gd0.2O1.9 samples were prepared starting from a commercial nanopowder and compared to the undoped material. The powder samples were pressed and afterwards sintered by a two-step procedure, before characterization by X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Impedance Spectroscopy (IS) in air. Cobalt or zinc additions are effective as sintering aid, allowing peak sintering temperatures around 1000°C to reach densifications above of 93% of theoretical density, showing no evidence for the presence of secondary phases. The total conductivity at 800 °C of pressed Zn-doped samples (6.7x10-2 S/cm) and Co-doped samples (7.5x10-2 S/cm) is similar for undoped samples (7.2x10-2 S/cm) showing that Zn and Co has a positive effect on densification without compromising the electrical conductivity.

This paper reports the outlet gas composition and phase change of electrodes during the CO–H2O reaction (CO + H2O → H2 + CO2) using an electrochemical cell with MnO–GDC (Gd-doped ceria: Ce0.8Gd0.2O1.9) cathode/porous GDC electrolyte/Fe3O4–GDC anode system. In the cathode, oxidation of MnO by H2O (3MnO + H2O → Mn3O4 + H2) and electrochemical reduction of Mn3O4 occurred (Mn3O4 + 2e− → 3MnO + O2−). In the anode, reduction of Fe3O4 by CO (Fe3O4 + CO → 3FeO + CO2) and electrochemical oxidation of FeO occurred (3FeO + O2− → Fe3O4 + 2e−). H2 and CO2 gases were produced through the above catalytic reactions. The fraction of H2 gas in the outlet gas increased at a high heating temperature and was 30–50% at 700 °C. As a parallel reaction of the CO–H2O reaction, the supplied CO gas was decomposed to CO2 and solid carbon over Fe3O4 in the anode at low temperatures (disproportion of CO, 2CO → CO2 + C).

This work reports on the study of steam reforming of methane under water deficient conditions over Ir/Ce 0.9 Gd 0.1 O 2-x (Ir/CGO) catalyst with very low Ir loading (0.1 wt% Ir). The catalyst surface was studied before and after testing by X-ray photoelectron spectrometry (XPS) and aberration-corrected high-resolution transmission electron microscopy (HRTEM) with 1 Å best resolution. Ir/CGO was pretreated at 1173 K in He flow with less than 0.5 ppm O 2 prior to catalytic testing. This led to the formation of Ir metal nanoparticles (NPs) with narrow-size distribution (2.5–6 nm, mean size of 4 nm in diameter). Ir/CGO slowly activated during reaction until reaching a steady state with tenfold increase of CH 4 conversion rate. The initial catalytic activity was consistent with surface metal sites being the main active sites and the CGO support having no effect on the CH 4 conversion rate except the inhibiting influence on the thermodynamically favoured carbon accumulation. After completion of the activation during reaction, Ir was present in the form of metallic NPs with smaller mean size (ca. 1.7 nm) than before testing, and oxidized Ir in 3+/4 + states. Metal support interactions were thought to be responsible for Ir oxidation and redispersion at the CGO surface during reaction. It is proposed that the improved catalytic activity is due to a synergy between highly dispersed Ir species and the CGO substrate through delocalization of the catalytic reactions in the vicinity of the Ir metal particles. [ABSTRACT FROM AUTHOR]

Strain-induced fast ion conduction has been a research area of interest for nanoscale energy conversion and storage systems. However, because of significant discrepancies in the interpretation of strain effects, there remains a lack of understanding of how fast ionic transport can be achieved by strain effects and how strain can be controlled in a nanoscale system. In this study, we investigated strain effects on the ionic conductivity of Gd0.2Ce0.8O1.9−δ (100) thin films under well controlled experimental conditions, in which errors due to the external environment could not intervene during the conductivity measurement. In order to avoid any interference from perpendicular-to-surface defects, such as grain boundaries, the ionic conductivity was measured in the out-of-plane direction by electrochemical impedance spectroscopy analysis. With varying film thickness, we found that a thicker film has a lower activation energy of ionic conduction. In addition, careful strain analysis using both reciprocal space mapping and strain mapping in transmission electron microscopy shows that a thicker film has a higher tensile strain than a thinner film. Furthermore, the tensile strain of thicker film was mostly developed near a grain boundary, which indicates that intrinsic strain is dominant rather than epitaxial or thermal strain during thin-film deposition and growth via the Volmer–Weber (island) growth mode. [ABSTRACT FROM AUTHOR]

Abstract: GdxCe1‐xO2‐δ (GDC) nanoparticles were synthesized, using continuous hydrothermal flow synthesis. By varying the synthesis conditions, particle size and morphology could be tailored. Here, particle sizes between 6 and 40 nm with polyhedral or octahedral shape could be obtained. Gd0.2Ce0.8O2‐δ nanoparticles were further processed into inks for inkjet printing. Despite the small particle size/large surface area, inks with excellent printing behavior were formulated. For proof‐of‐concept, thin GDC layers were printed on a) green NiO‐GDC substrates, and on b) presintered NiO‐YSZ substrates. While no dense layers could be obtained on the green NiO‐GDC substrates, GDC nanoparticles printed on NiO‐YSZ substrates formed a dense continuous layer after firing at 1300°C. [ABSTRACT FROM AUTHOR]

Highly porous NiO–gadolinium-doped ceria (GDC) nano-composite powders are synthesized by a one-pot glycine nitrate process and applied to the fabrication of Ni–YSZ (yttria-stabilized zirconia)-supported tubular solid oxide fuel cells (SOFCs) with a cell configuration of Ni–YSZ/Ni/Ni–GDC/GDC/LSCF (La0.6Sr0.4Co0.2Fe0.8O3−δ)–GDC/LSCF. The power density of the cell is as high as 413 mW cm−2 at 600 °C, which is 1.37 times higher than that of an identically configured cell fabricated using ball milling-derived NiO–GDC powders (301 mW cm−2). The high porosity of the powders and the good mixing between the NiO and GDC primary nanoparticles due to the abrupt combustion of the precursors effectively suppress the densification, coarsening, and agglomeration of NiO and GDC particles during sintering, resulting in a highly porous Ni–GDC anode layer with good dispersion of Ni and GDC particles and a cell with significantly enhanced power density.

The present work reports the influence of chemical synthesis on structural, morphological and optical properties of gadolinium-doped ceria (GDC) with analytical characterization of synthesized specimens. GDC powders with Gd content of 10, 15 and 20 mol% were synthesized by aqueous sol-gel and sol-gel combustion methods using glycerol as complexing agent and fuel. The phase purity and structural features of obtained powders were evaluated using X-ray diffraction analysis and Raman spectroscopy. These studies confirmed that crystallization of GDC occurs into cubic fluorite-type crystal structure. Morphological features as well as optical properties of GDC powders were determined to be strongly dependent on the synthesis method. To confirm chemical composition of prepared samples, spectrophotometric approach for the determination of Ce and Gd in GDC samples was suggested. Relative standard deviation values for Ce and Gd were in the range of 1.5-4.1 and 2.0-5.6%, respectively. The obtained results demonstrated that the suggested analytical procedure can be successfully used for the analysis of GDC specimens with high accuracy. [ABSTRACT FROM AUTHOR]

Gadolinium-doped ceria (known as CGO or GDC) is a good oxide-ion conductor which presents potential application for solid-state electrochemical devices. However, one of the main drawbacks of this material is the high sintering temperature required to obtain dense ceramic. In this paper, we report a new way to reduce densification temperature of CGO by adding x weight percent of La 2 Mo 2 O 9 material (0≤ x ≤10). This latter is also a good oxide-ion conductor at high temperature (>580 °C) which allows the preservation of the electrochemical properties of CGO as shown by impedance spectroscopy. The sintering behavior is then studied using dilatometric measurements and mechanism of densification is discussed. [ABSTRACT FROM AUTHOR]