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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 large thermal gradient annealing on the microstructure of 10 mol% gadolinium doped ceria (GDC) were investigated. GDC powder was prepared by solvent deficient method and sintered at 1650 °C for 10 h to achieve dense ceramics with ~8 μm grain size. The densified GDC samples were subsequently annealed using a 60 W infrared laser at over 2100 °C for 1 h under a thermal gradient equivalent to ~0.3–0.5 °C/μm. The post-annealed samples at 2150 °C for 1 h exhibit grains with average length and width of 37 and 28 μm, respectively. Electron backscattered diffraction (EBSD) analysis revealed that the post-annealed sample at 2150 °C consists of grains oriented close to five principal directions ( , and on [0 0 1], and and on [0 1 0]) within a tolerance angle of ±10°, whereas the grains of the pre-annealed sample are randomly oriented. Gadolinium diffuses 20–30 μm away from the irradiated surface, with the measured composition of regions deeper than 30 μm, Ce0.86Gd0.14O1.93, is close to that of the pre-annealed sample, Ce0.87Gd0.13O1.94. Enhancement of total conductivity of the post-annealed GDC (1.1 × 10-3 S cm-1 at 500 °C, and 2.1 × 10-2 S cm-1 at 700 °C) is observed when compared to the pre-annealed GDC (3.1 × 10-5 S cm-1 at 500 °C, and 1.7 × 10-3 S cm-1 at 700 °C), and points to the decrease in the grain boundary (GB) resistivity. This could be attributed to both the change in GB area and grain alignment.

The deconvolution of physicochemical processes in impedance spectra of SOCs with nickel/ceria fuel electrodes is challenging as gas diffusion strongly overlaps with the electrochemical processes at fuel and air electrode. To overcome this issue, symmetrical cells were applied and the gas diffusion process at the fuel electrode was quantified by altering the inert component (nitrogen/helium) in a ternary fuel gas mixture. An effective gas transport parameter considering microstructural and geometrical features was derived, enabling a precise quantification of polarization resistances related to gas diffusion and hydrogen electrooxidation. The obtained values were applied to parameterize an existing dc cell model. The model validation in fuel cell and electrolyzer mode showed an excellent agreement between measured and simulated current/voltage characteristics over a wide range of technically meaningful gas compositions and operating temperatures.

Low-temperature solid oxide fuel cells (LT-SOFC) are usually fabricated using ultra-thin yttria-stabilized zirconia electrolyte films and Pt electrodes. This paper studies the possibility of creating LT-SOFCs using the traditional ceramic materials such as the NiO/GDC (GDC - gadolinium doped ceria) anode, GDC electrolyte, and La0.6Sr0.4CoO3 (LSC) cathode. The anode/electrolyte bilayer structure is prepared on porous anodic aluminium oxide substrates using magnetron sputtering. The microstructure of the obtained bilayer structure is investigated before and after high-temperature annealing in air. The fuel cells are fabricated with the LSC cathode; their current-voltage characteristic and electrochemical impedance spectra are measured in the temperature range of 450–600°C.

Understanding and modelling complex phenomenon in solid oxide fuel cell electrodes require information about their three dimensional microstructures. However, measuring the 3-D micro- and nano-structures requires complex and time-consuming data acquisition technique such as focused ion beam - scanning electron (FIB-SEM) tomography. Meanwhile, obtaining a single 2-D cross-sectional SEM image is relatively simple. A new algorithm for synthetic 3-D microstructure generation from 2-D cross-section is proposed in the present study. The algorithm is based on the generative adversarial network (GAN) composed of a 3-D generator and a 2-D discriminator, which uses only 2-D images as a training data. The applicability of the proposed method is tested on nickel (Ni) – gadolinium doped ceria (GDC) anodes. The synthetic 3-D microstructures are compared with those obtained from FIB-SEM. The proposed method can be easily adapted for any type of materials and imagining techniques.

In this study, Gd and Ca co-doped ceria electrolytes with the compositions of Ce0.8Gd0.2–xCaxO2–δ (x = 0–0.08) were prepared by a novel gel-casting method. The effects of the addition of Ca on the phase compositions, sintering behavior, and electrical properties of samples were investigated. According to the scanning electron microscope results and relative density measurement results, it is found that the addition of particular quantity of CaO can promote the sintering densification with a uniform grain growth. When the sintering temperature is 1400 °C, the sample with 6 mol% addition of Ca has the highest relative density, which reaches 98.5% of the theoretical density. The electrical properties testing results confirm that the electrical conductivity of the samples can be improved significantly by doping appropriate CaO content. The maximum conductivity of 0.082 S/cm can be obtained at 800 °C in the Ce0.8Gd0.12-Ca0.06O1.87 sample. It suggests that CaO can be used as an effective sintering aid and a co-dopant on the optimization of electrical properties for ceria-based electrolytes.

The local activation overpotential describes the electrostatic potential shift away from equilibrium at an electrode/electrolyte interface. This electrostatic potential is not entirely satisfactory for describing the reaction kinetics of a mixed ionic–electronic conducting (MIEC) solid-oxide cell (SOC) electrode where charge transfer occurs at the electrode–gas interface. Using the theory of the electrostatic potential at the MIEC–gas interface as an electrochemical driving force, charge transfer at the ceria–gas interface has been modelled based on the intrinsic dipole potential of the adsorbate. This model gives a physically meaningful reason for the enhancement in electrochemical activity of a MIEC electrode as the steam and hydrogen pressure is increased in both fuel cell and electrolysis modes. This model was validated against operando XPS data from previous literature to accurately predict the outer work function shift of thin film Sm0.2Ce0.8O1.9 in a H2/H2O atmosphere as a function of overpotential.

Gadolinium-doped ceria (GDC) is an important fast oxygen ion conductor. O2--ion hopping in different cation environments of GDC is probed using molecular dynamics (MD). We find that at equilibrium, the O2--ions and vacancy defects arrange themselves around the relatively immobile cations in a way such that pairs of O2--ions and vacancy defect (O2--vac pair) are in greater numbers in some cation environments than others. The difference in O2--vac pair numbers is shown to originate from entropic effects in the cation environments. As a consequence of the entropic effect, the O2--vac pair distribution is practically independent of temperature between 974 and 1874 K. Even the O2- ion hopping rate and barrier are influenced by the entropic effect. This observation is in stark contrast with the standard belief that energetic interactions dominate in solid oxide materials, and entropic factors can be ignored. By analyzing the cation environment effect using k-means clustering, nine environment clusters are identified that are associated with unique values of the activation barrier and entropy. Comparisons to yttria stabilized zirconia (YSZ), yet another popular fast oxygen ion conductor, are made.

Intermediate temperature solid oxide fuel cells (IT-SOFC) require an effectively functioning cathode layer whose performance depends largely on their microstructures. Improved electrochemical performance of the cathode layer can be possible by tailoring the microstructure to ensure that both the oxygen reduction reaction (ORR) occurs fast along the triple-phase boundaries (TPB) and the diffusion pathway is short enough for fast ion diffusion through the cathode layer. Electro spray deposition (ESD) method is a low-cost deposition method which allows the optimization of microstructure by changing the spraying parameters. In this study, gadolinium doped ceria (GDC) electrolyte layer is deposited with La1-xSrxCo1-yFeyO3-δ (LSCF) derived from polymeric precursor salts, symmetrically. As a solvent couple, 2-butoxyethanol and ethylene glycol are used instead of the conventional solvent couples frequently employed in the literature. The use of the new type of solvents in the precursor solution leads to promising results on modifying the microstructure of the deposited layer. The effect of electrospraying parameters on the cell performance was also studied. Promising results were obtained as measured by impedance spectroscopy when this new solvent couple was employed.

Improvement of the sluggish oxygen reduction reaction (ORR) is the key to lower the operating temperature of conventional solid oxide fuel cells (SOFCs). Developing a novel nanostructure in the cathodic catalyst layer is one of the efficient ways to reduce the operating temperature while improving fuel cell performance. In this paper, all components of low-temperature SOFCs were prepared on a nanoporous substrate by the sputtering method. For the performance enhancement at low temperature, an ultrathin Pt-Gadolinium Doped Ceria (GDC) cermet interlayer was deposited on the cathode side of electrolyte and demonstrated. A significant improvement in electrochemical performance was observed in the Pt-GDC interlayer fuel cell compared to a reference cell. The peak power density of Pt-GDC cathodic cermet interlayer cell was 334 mW/cm2 at 500 °C, which was 42.7% higher than that of the reference cell. Through additional analysis, we confirmed that the observed performance enhancement was attributed to the ultrathin cathodic cermet interlayer, which increases the triple phase boundary and enhances the reaction kinetics for ORR.

Maintaining the original advantages of symmetrical solid oxide fuel cells (SSOFCs), the electrochemical performance can be further enhanced by new quasi-symmetrical solid oxide fuel cells. Herein, highly active Ruddlesden-Popper oxides Co-doped LaSr3Fe3O10-δ are investigated as possible symmetric electrodes for SSOFCs, and in situ exsolution of Co–Fe nanoparticles can be homogenously observed on the backbone of this catalyst after high temperature hydrogenation. Spin coated gadolinium doped ceria (GDC) buffer layer onto both sides of the YSZ electrolyte is used to avoid the side reaction of YSZ electrolyte and the symmetric electrodes. LaSr3Fe2CoO10-δ showed more excellent electrochemical performance with the high maximum power density of 351.4 mW cm−2 and the electrode polarization resistance of 0.2894 Ω cm2 at 800 °C. Moreover, no sign of degradation with this SSOFCs during 100 h long-time testing is observed at 700 °C, indicating that the LaSr3Fe2CoO10-δ symmetrical electrode exhibits good redox reversibility. The high stability and catalytic activity of Ruddlesden-Popper oxides can provide more promise related applications for SSOFCs.

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.

In this study, Ce0.89+xGd0.1−2xSrxEu0.01O2−δ (x = 0–0.04) ceramic electrolytes sintered at different temperatures were prepared and the impurity scavenging effect of Sr2+ dopants on their grain boundary (GB) electrical properties were investigated. The phase compositions, microstructures, and ionic conductivities of the samples were investigated using X-ray diffraction, scanning electron microscopy, and AC impedance spectroscopy, respectively. The incorporation of Sr2+ improved the overall GB conduction of the electrolytes by decreasing their GB area and space-charge potential. It hindered conduction to some extent by weakening the impurity dilution effect. The scavenging effect could be observed only when the sintering temperature was higher than the eutectic temperature of Si GB impurities. At low sintering temperatures, the Sr2+ dopants could not scavenge the GB impurities and increased the GB impurity coverage proportion. The findings of this study provide insights into the optimisation of the GB electrical properties of oxygen-ion conductors by selecting appropriate dopants and sintering temperatures to induce the GB impurity scavenging effect.

Using room temperature sputtering, we have deposited Gd0.1Ce0·9O1.95 buffer layers at the cathode/electrolyte interface of 10 cm2 circular Solid Oxide Fuel Cells. By suitably selecting the in air annealing step, we show the possibility to control the granular properties of the Gd0.1Ce0·9O1.95 buffer layers in order to optimize the Solid Oxide Fuel Cell's electrical performances. In particular, we maximise the buffer layer grain density via an annealing process with a plateau temperature of 800 °C, obtaining improvements in the final Solid Oxide Fuel Cell performances with an 8% increase in the current density at 800 mV and 700 °C with respect to the Solid Oxide Fuel Cell annealed at 1050 °C, and with a 59% increase in the current density at the same voltage and temperature when compared to the standard cells with the Gadolinium Doped Ceria buffer layer produced by lithographic processes. The achieved optimization procedure clearly illustrates the potentiality of the room temperature sputtering process followed by in-air annealing step in the control of the granularity of the deposited layers. Moreover, the obtained results open the way to further studies about the industrial scalability of the used technique and to its implementation in practical large scale cell production process.

Neste trabalho, os nanocompósitos de interesse foram preparados, utilizando-se o Método dos Precursores Poliméricos, por meio do qual se prepararam os citratos de céria dopados com 10, 15 e 20% de gadolínio, e encapsularam-se com 3% em mol de ZrO2, em diferentes temperaturas. Para a caracterização dos materiais obtidos, utilizaram-se as técnicas de Difração de Raios X e Emissão Fotoluminescente. Verifiou-se que a alta concentração do dopante ocasiona tanto a melhoria na emissão, pela adição de defeitos, quanto a diminuição, pelo quenching da emissão. O aumento na temperatura de tratamento térmico também reduz a emissão, uma vez que diminui a quantidade de defeitos.

Mixed ionic and electronic conducting (MIEC) materials recently gained much interest for use as anodes in solid oxide fuel cell (SOFC) applications. However, many processes in MIEC-based porous anodes are still poorly understood and the appropriate interpretation of corresponding electrochemical impedance spectroscopy (EIS) data is challenging. Therefore, a model which is capable to capture all relevant physico-chemical processes is a crucial prerequisite for systematic materials optimization. In this contribution we present a comprehensive model for MIEC-based anodes providing both the DC-behaviour and the EIS-spectra. The model enables one to distinguish between the impact of the chemical capacitance, the reaction resistance, the gas impedance and the charge transport resistance on the EIS-spectrum and therewith allows its appropriate interpretation for button cell conditions. Typical MIEC-features are studied with the model applied to gadolinium doped ceria (CGO) anodes with different microstructures. The results obtained for CGO anodes reveal the spatial distribution of the reaction zone and associated transport distances for the charge carriers and gas species. Moreover, parameter spaces for transport limited and surface reaction limited situations are depicted. By linking bulk material properties, microstructure effects and the cell design with the cell performance, we present a way towards a systematic materials optimization for MIEC-based anodes.

We investigate the influence of position, under large circular sputtering targets, on the final electrochemical performance of 35 mm diameter button solid oxide fuel cells with sputter-deposited Gadolinium doped Ceria barrier layers, positioned in order to almost cover the entirety of the area associated with a 120 × 80 mm2 industrial cell. We compare the results obtained via structural and morphological analysis to the Electrochemical Impedance Spectroscopy (EIS) measurements performed on the button cells, disentangling the role of different parameters. The Atomic Force Microscopy analysis makes it possible to observe a decrease in the roughness values from the peripheral to the central zones under the sputtering target, with peak-to-valley roughness values, respectively, decreasing from 380 nm to 300 nm, while Scanning Electron Microscopy and Energy Dispersive Spectroscopy show a dependence of the layer coverage from the position. The electrochemical performances of button cells with buffer layers of only 200 nm in thickness, and with negligible thickness gradients across them, show current density values of up to 478 mA/cm2 at 0.8 V and 650 °C, with an improvement of more than 67% with respect to button cells with standard (screen printed) buffer layers. These results point out the major influence exerted by parameters such as the thickness gradient and the coverage of the sputtered buffer layers in determining the final electrochemical performances.

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.

Metal-supported solid oxide fuel cells (MSCs) are promising candidates for mobile power generators like range extenders for battery electric vehicles due to their improved thermal conductivity and ruggedness. The limited space available in such vehicles heightens the need to achieve high power densities. In the present study, a significant increase in cell performance of the MSC concept of Plansee SE was demonstrated by means of systematic microstructure optimization of the complete cell architecture based on improved processing. Thickness and roughness of multi-layered Ni/GDC anode play a particularly important role in improving cell performance. After several optimization steps, a notable increase of current density from 1.29 A/cm2 to 1.79 A/cm2 at 700 °C and 0.7 V (+38%) was achieved. Additionally, lowering the anode roughness enables clear reduction of electrolyte thickness down to 2 μm, a starting point for the further enhancement of cell performance.

The technological feasibility of electrophoretic deposition (EPD) of gadolinium doped ceria (GDC) on polypyrrole (PPy) coated yttrium stabilized zirconia (YSZ) has been reported. To enhance the EPD technique for the fabrication of GDC layer and to deepen the understanding of EPD, the fundamental characteristics of EPD of GDC on PPy coated YSZ were investigated. The deposition rate of GDC on PPy coated YSZ is slower than that on graphite under the same voltage. An H+ ion accumulation zone is formed in the vicinity of PPy coated YSZ after applying the voltage. The thickness of this ion accumulation zone initially increases and then decreases. Finally, the ion accumulation zone is replaced by an ion depletion zone. The absorbed H+ ions are desorbed from the particles after deposition and are then reduced to hydrogen gas. The reduction of absorbed H+ ions and free H+ ions corresponds to the deposition and the unavoidable side reaction, respectively. A new parameter, f, the percentage of electric charged associated with the reduction of absorbed H+ ions in the total charge, is introduced to reflect the competitive relationship between the deposition and the inevitable side reaction. f decreases with the increase of current density.

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) over dot ) 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, Ce0.9Gd0.1O2-delta, delta = 0.05. Nanometric starting powders of ca. similar to 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. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In this work, nanocrystalline layers based on the Pr, Gd co-doped CeO2 were investigated. For the preparation of thin layers, low-temperature spray pyrolysis technique was used. Different stoichiometries of the layers were produced for comparison on polished sapphire substrates. The microstructure of the prepared thin layers was studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and x-ray diffractometry (XRD). The total electrical conductivity as a function of Gd or Pr dopant were determined by DC electrical measurements using the Van der Pauw method in air atmosphere. The oxygen electrode interface analysis confirm protective character of the diffusion barrier layer based on doped CeO2.

Series of Gd3+ and Mg2+ co-doped ceria (Ce0.8Gd0.2-xMgxO1.9-?) powders were prepared by a sol-gel method and electrolyte ceramics were obtained by sintering at 1300?C. Thermogravimetric and differential scanning calorimetry, X-ray diffraction, scanning electron microscope and electrochemical impedance spectroscopy were used for structural, morphology and electrical characterization of the prepared samples. Well crystalline cubic fluorite structured composite was confirmed after calcination at 700?C and the electrolyte ceramics sintered at 1300?C for 4 h was quite dense with uniform microstructure. The electrochemical analysis results displayed that the highest conductivity has the Ce0.8Gd0.14Mg0.06O1.87 compound, i.e. 0.0203 S/cm at 800?C. Therefore, it was concluded that co-doping with Gd3+ and Mg2+ could enhance the electrical properties of the CeO2 based solid electrolytes.

Lithium-gadolinium-doped ceria electrolytes (2–5 mol% of lithium) are prepared by fast and reliable one-pot sol gel combustion synthesis and sintered at low temperature. The aim is to improve the microstructure, electrochemical and power generation of electrolyte-supported intermediate temperature solid oxide fuel cells. Time-of-flight coupled secondary ions mass spectroscopy and transmission electron microscopy reveal the uniform distribution of lithium and the structural modification and surface change induced by the doping. Lithium addition reduces the sintering temperature to 950 °C, and the electrochemical properties compared to the pure gadolinium doped ceria are highly superior. A maximum of 3.59·10−2–1.41·10−1 S·cm−1 for total conductivity are achieved for 3 mol.% of lithium addition at intermediate operative temperature range. An electrolyte-supported solid oxide fuel cell is then fabricated and tested in different gas conditions and operative temperatures. The maximum power density is 359 mW·cm−2 at 668 mA·cm−2 (750 °C). The results demonstrate the reliability, the short time-to-product and the feasibility of both synthesis cycle and electrolyte production for industrial application to develop a cost-effective and marketable fuel cell technology.

Gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolytes have received significant attention for use in solid oxide fuel cells since this electrolyte enables the use of a cobalt-containing cathode, which show a high performance at low temperature. However, the low sintering temperature of the bilayer electrolyte, which is required to avoid side reactions, results in low density, limiting its practical applications. In this study, we report a facile and cost-effective method for the fabrication of dense gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolytes at low temperatures. Even at a low sintering temperature of 1250 °C, a thin and dense bilayer electrolyte structure was achieved using an isostatic pressure process on the dip-coated electrolyte layers and anode support substrate. Solid oxide fuel cells adopting this dense gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolyte exhibited high power density of 1.251 W cm−2 at 650 °C and high stability for 100 h. These significant improvements in performances is attributed to the greatly reduced porosity (

Fully nanostructured La0.6Sr0.4Co0.2Fe0.8O3-δ/Gd0.2Ce0.8O1.9 [lanthanum strontium cobalt ferrite (LSCF)/gadolinium-doped ceria (GDC)] composite cathode is successfully demonstrated with conventional powder processing using nanocomposite particles, grown via a colloidal-processing-based bottom-up approach, as starting material. The cathode/electrolyte interface adheres well at a relatively low temperature of 900 °C because of the promoted surface diffusion of constituent elements by the higher surface energy of the nano-sized particles. By contrast, successful fabrication of a nanostructured porous cathode composed of uniformly distributing LSCF and GDC grains with a diameter of 50–70 nm strongly supports the prevented grain growth and pore closure by the co-existing hetero-phases in the composite particles acting as bulk diffusion barrier of each other's constituents during sintering. The nanocomposite cathode exhibits quite low area-specific polarization resistances for oxygen reduction reaction (ORR) of 0.127, 0.054, 0.032, 0.015 and 0.009 Ω cm2 at 600, 650, 700, 750 and 800 °C, respectively. These are significantly lower than those reported in the literature. The highly accelerated ORR kinetics contribute directly to the very high power densities of the anode-supported cells of 0.40, 0.77, 1.40, 2.32, and 3.29 W cm−2 at 600, 650, 700, 750, and 800 °C, respectively, with a cell voltage at 0.7 V.

Journal of the American Ceramic Society (2021). doi:10.1111/jace.17614, Published by Wiley-Blackwell, Oxford [u.a.]

Flash sintering was discovered in 2010, where a dog- bone- shaped zirconia sample was sintered at a furnace temperature of 850°C in

The deconvolution of physicochemical processes in impedance spectra of SOCs with nickel/ceria fuel electrodes is challenging as gas diffusion strongly overlaps with the electrochemical processes at fuel and air electrode. To overcome this issue, symmetrical cells were applied and the gas diffusion process at the fuel electrode was quantified by altering the inert component (nitrogen/helium) in a ternary fuel gas mixture. An effective gas transport parameter considering microstructural and geometrical features was derived, enabling a precise quantification of polarization resistances related to gas diffusion and hydrogen electrooxidation. The obtained values were applied to parameterize a dc cell model. The model validation in fuel cell and electrolyzer mode showed an excellent agreement between measured and simulated current/voltage characteristics over a wide range of technically meaningful gas compositions and operating temperatures.

Solid Oxide Cells (SOC), as a key energy-conversion technology, require sintering at temperatures exceeding 1200 °C, which tend to coarsen the structure of the fuel electrode. Nanostructured electrodes with high surface areas can help to decrease the electrode resistance and facilitate the operation of the SOC stacks at low temperatures with current collectors made from cheaper steel types. In this paper, we demonstrate and carefully evaluate a novel low-temperature manufacturing method for nanostructured Strontium Iron Molybdenum Oxide (SFM)/Gadolinium Doped Ceria (CGO) composite electrodes. The composite electrodes are applied on both sides of a Zr-based electrolyte with CGO barrier layers and sintered at 800 °C for 3 h in a 5% H2/N2 atmosphere. The preparation parameters, thermal behavior, and electrode microstructure are studied to improve electrochemical performance. Based on the fitting of Nyquist plots, the electrochemical performance is mainly limited by two reactions in series at low frequency, in the 0.08–1 Hz and 1–50 Hz ranges. The electrode polarization resistance is almost constant at 1.24 Ω cm2 for 110 h at 750 °C in 60 vol% CO/CO2.

A nanocomposite, containing gadolinium-doped ceria (GDC, Ce0.85Gd0.15O1.925) and 10 mol% gadolinium-doped barium cerate (BGC, BaCe0.85Gd0.15O2.925), was developed as an electrolyte material for intermediate temperature-solid oxide fuel cell. The composite powder was synthesized through an auto-combustion process that yielded the desired phases right after combustion. The powder was characterized using X-ray diffraction, particle size analysis, Brunauer–Emmett–Teller surface area analysis and transmission electron microscopy. The electrical properties of the composite electrolyte were characterized by electrochemical impedance spectroscopy under air as a function of temperature. The effect of second phase on total conductivity and activation energy of the composite material was compared with that of GDC of similar composition. For this, GDC (Ce0.85Gd0.15O1.925) powder was produced using a similar processing technique. The microstructural characterization of GDC and GDC–10BGC composite materials was studied through scanning electron microscopy. The electrochemical properties of planar cell, using GDC–10BGC as electrolyte and employing Ni–(GDC–10BGC) and La0.6Sr0.4Co0.2Fe0.8O3-δ-based anode and cathode materials, were investigated.

Porous buffer layers for anode-supported solid oxide fuel cells (SOFCs) have been investigated for many years with different thicknesses of the buffer layer in each study. In this work, micro-tubular SOFCs having samarium-doped ceria (SDC) and gadolinium-doped ceria (GDC) buffer layers are compared using the current–voltage technique, electrochemical impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The thickness of the porous SDC and GDC buffer layer is investigated systematically with the thickness varying between 0.3 and 2.0 μm. The power density varies between 212 and 1004 mW/cm2 for samples having different SDC buffer layer thickness. Comparable changes occur for the SOFCs with a GDC buffer layer, but less variation in polarization losses resulted. Variation in electrochemical performance varies due to changes in ohmic resistance, cathode activation polarization, and interfacial reactions between the cathode and electrolyte materials.

Mixed ionic electronic conductors (MIECs) have attracted increasing attention as anode materials for solid oxide fuel cells (SOFCs) and they hold great promise for lowering the operation temperature of SOFCs. However, there has been a lack of understanding of the performance-limiting factors and guidelines for rational design of composite metal-MIEC electrodes. Using a newly-developed approach based on 3D-tomography and electrochemical impedance spectroscopy, here for the first time we quantify the contribution of the dual-phase boundary (DPB) relative to the three-phase boundary (TPB) reaction pathway on real MIEC electrodes. A new design strategy is developed for Ni/gadolinium doped ceria (CGO) electrodes (a typical MIEC electrode) based on the quantitative analyses and a novel Ni/CGO fiber–matrix structure is proposed and fabricated by combining electrospinning and tape-casting methods using commercial powders. With only 11.5 vol% nickel, the designer Ni/CGO fiber–matrix electrode shows 32% and 67% lower polarization resistance than a nano-Ni impregnated CGO scaffold electrode and conventional cermet electrode respectively. The results in this paper demonstrate quantitatively using real electrode structures that enhancing DPB and hydrogen kinetics are more efficient strategies to enhance electrode performance than simply increasing TPB.

The influence of copper addition (0.5&ndash, 2 mol%) on the crystal structure, densification microstructure, and electrochemical properties of Ce0.8Gd0.2O1.9 synthesized in a one-step sol&ndash, gel combustion synthesis route has been studied. It has been found that Cu is very active as sintering aids, with a significative reduction of GDC firing temperature. A reduction of 500 &deg, C with a small amount of copper (0.5 mol%) was observed achieving dense bodies with considerable ionic conductivities. Rietveld refined was used to investigate the crystal structure while relative density and microstructural examination were performed in the sintering temperature range of 1000&ndash, 1200 &deg, C after dilatometer analysis. High dense bodies were fabricated at the lowest sintering temperature, which promotes the formation of Ce0.8(1&minus, x)Gd0.2(1&minus, x)CuxO[1.9(1&minus, x)+x] solid solution and the absence of secondary phase Cu-rich or the segregation or copper at the grain boundary. As compared to the pure GDC an improvement of total conductivity was achieved with a maximum for the highest copper content of 2.23·10&minus, 3&ndash, 9.19·10&minus, 2 S cm&minus, 1 in the temperature range of 200&ndash, 800 &deg, C.

Made available in DSpace on 2020-12-12T01:14:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-06-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) 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 Ce0.8Gd0.2O1.9 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. São Paulo State University (UNESP) School of Sciences and Engineering Graduate Program in Materials Science and Engineering Department of Materials Engineering Federal University of São Carlos São Paulo State University (UNESP) School of Sciences and Engineering

Nickel-gadolinium doped ceria (Ni-GDC) composite anodes gain a lot of attention as they have potential to be a beneficial solution for the intermediate temperature solid oxide fuel cells. In this paper, the influence of the initial microstructure of Ni-GDC anode on the polarization characteristics and its deterioration in 100h operation are investigated. The initial microstructures of the investigated anodes are determined by the different sizes and aspect ratios of the GDC powders, but all anodes having the same initial compositions of NiO:GDC = 60:40 vol.%. It was found that the anode with the smallest GDC particle had the best initial performance, but also underwent the most severe degradation. The microstructures of the fabricated anodes were investigated by focused ion beam - scanning electron microscopy (FIB-SEM), and microstructural parameters were quantified to relate the electrochemical performance. From the experimentation, contribution of the Ni-GDC microstructure to the anode polarization characteristics is discussed. The morphological evolution after the operation is also in discussion, especially those of the GDC phase. It was concluded that the mobility of GDC could be an influential factor determining the change in polarization resistance.

ECS journal of solid state science and technology : JSS 8(1), P41-P50 (2019). doi:10.1149/2.0181901jss special issue: "JSS Focus Issue on Recent Advances in Wide Bandgap III-Nitride Devices and Solid State Lighting : A Tribute to Isamu Akasaki", Published by ECS, Pennington, NJ

Composite electrolyte of gadolinium doped ceria and lithium sodium carbonate ((LiNa)2CO3-GDC) showing enhanced stability and mechanical strength has been fabricated using melt infiltration technique and tested as solid oxide fuel cell (SOFC) electrolytes. Porous matrix of GDC is fabricated by sintering at 1450 °C and subsequently the prefabricated matrix is melt infiltrated with mixture of (LiNa)2CO3 (1:1 wt ratio). Ionic conductivities of the electrolytes, current-voltage characteristics and impedance spectra of the electrolyte supported bilayers with hydrogen as fuel and air as oxidant are measured. Physical characteristics of the composite electrolytes analysed using X-ray diffraction, scanning electron microscope (SEM), energy dispersive spectroscope, fourier transform infrared spectroscope and thermal gravimetric analysis show spatial distribution of active interphases, where in pore filled with (LiNa)2CO3 melt into prefabricated GDC matrix. As carbonate phase completely fills the GDC matrix, the ionic conductivity of melt infiltrated 30 wt% (LiNa)2CO3-GDC composite electrolyte is comparable to that of the solid state synthesised electrolyte at 600 °C. The performance of melt infiltrated 30 wt% (LiNa)2CO3-GDC composite electrolyte (∼2 mm) is much better (223 mW cm−2 at 579 mA cm−2) than that prepared by solid state method at 750 °C. The morphology, thermal analysis and electrochemical studies of melt infiltrated composite electrolytes reveal better cell performance due to well sintered stable structure.

Nanostructured ceramic materials have high conductivity compared to bulk materials. Ceria based systems, with fluorite structure, [samarium doped ceria (SDC) and gadolinium doped ceria (GDC)] are found to be the best electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFC). In the present study, Ce0.8Gd0.1Sb0.1O2-δ nanostructured materials were synthesized by wet co-precipitation method. X ray diffraction pattern confirms the crystallization of the sample in the most conducting cubic fluorite phase. The presence of Ce, Gd, and Sb in the sample is qualitatively confirmed by Fourier transform infrared spectroscopy. Scanning electron spectroscopy image shows mesoporous nature of the sample. The addition of Sb3+ to the GDC system reduces the sintering temperature by 33.33%. The dielectric studies show that the prepared sample is an ionic material with two types of conduction mechanisms – grain interior and grain boundary. Hence, two different activation energies for ionic conduction are obtained for the sample at low and high temperature region.

This work evaluates porous Sr0.86Ti0.65Fe0.35O3 (STF35) as a possible oxygen electrode material for Solid Oxide Cells. The powder synthesis was performed by solid state method. Characterization included DC electrical conductivity study of sintered bulk samples and impedance spectroscopy study of symmetrical electrodes deposited on gadolinium doped ceria substrates. Measurements were carried out in atmospheres with different pO2 levels: 0.1%–20% O2. Detailed equivalent circuit analysis was carried out in order to clarify the reaction pathway on porous electrode, which extends knowledge available for dense model electrodes. At 800 °C in 21% O2, the DC electrical conductivity of STF35 pellet was 0.6 S cm−1 and the polarization resistance of the electrode in the symmetrical cell was ∼100 mΩ cm2. Detailed impedance spectroscopy studies revealed that the largest contribution (∼80%) towards the polarization resistance is due to oxygen adsorption, which is limiting the oxygen reduction performance of the porous STF35 electrode. These results show the applicability of advanced impedance analysis methods (e.g. Distribution of Relaxation Times - DRT) for description of complex impedance electrode phenomena of porous electrodes.

High proton conductivity and chemical stability of electrolyte materials are the bottleneck challenges to be overcome for the practical feasibility of protonic ceramic fuel cells (PCFCs). Therefore, the fundamental electrochemical properties of electrolyte materials under cell operating conditions are critical. In this study, the partial conductivities, mobilities, and equilibrium constants of the electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711) are determined by a DC four-probe conductivity measurement in the temperature range of 600–750 °C. The electrolyte acts as a proton conductor due to the dominant proton regime with a conductivity of 1.3 × 10−2 S cm−1 under an air atmosphere (3% H2O) at 600 °C, whereas mixed-ion conduction appears from 750 °C. The theoretical power densities were calculated from both oxygen ion and proton chemical potential gradient profiles based on the partial conductivities of the mobile charge carriers in the electrolyte. The results show a theoretical peak performance of around 5.28 W cm−2 for a 10 μm thick electrolyte at 600 °C without considering any electrode polarization. Most importantly, at this temperature, the peak performance of the BZCYYb1711 electrolyte is remarkable, about two times higher than that of conventional oxygen ion conductors, yttrium doped zirconia (YSZ) and gadolinium doped ceria (GDC), as an electrolyte for SOFCs. This indicates that the perovskite proton conductor BZCYYb1711 is an excellent candidate for a protonic fuel cell operated at intermediate temperatures (≤600 °C). Consequently, our work provides performance limits based on the transport properties of the electrolyte as a guideline for the further development of suitable electrode materials for PCFCs.