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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.

Cycle stability is crucial for non-aqueous lithium-oxygen batteries, which is dependent with the cathode performance. In this work, gadolinium doped CeO2 nanoparticles are prepared through one-pot hydrothermal process on reduced graphene oxide, and applied as cathode catalyst for non-aqueous lithium-oxygen batteries. With the catalytic effect of Ce0.8Gd0.2O2-δ nanoparticles on Li2O2 formation and decomposition, the battery delivers both low discharge and charge overpotential about 0.18 V and 0.69 V at the current density of 400 mA g−1. Moreover, cycle stability is enhanced for over 100 times at the capacity limitation of 600 mAh·g−1. The superiority may attribute to the enhanced stabilization of Ce0.8Gd0.2O2-δ nanoparticles through doping process, which can preserve the nanoparticles from migration and aggregation during cycle process.

This work presents an analysis of the long-term behavior of nickel/gadolinium-doped ceria (CGO) anode-based solid oxide fuel cells (SOFC) under sulfur poisoning conditions. A parameter study of sulfur-induced irreversible long-term degradation of commercial, high-performance single cells was carried out at 900 °C for different H2/N2/H2S fuel gas atmospheres, current densities and Ni/CGO anodes. The poisoning periods of the cells varied from 200 to 1500 h. The possibility of stable long-term Ni/CGO anode operation under sulfur exposure is established and the critical operating regime is outlined. Depending on the operating conditions, two degradation phenomena can be observed. Small degradation of the ohmic resistance was witnessed for sulfur exposure times of approximately 1000 h. Moreover, degradation of the anode charge transfer resistance was observed to be triggered by the combination of a small anodic potential step and high sulfur coverage on Ni. The microstructural evolution of altered Ni/CGO anodes was examined post-mortem by means of SEM and FIB/SEM, and is correlated to the anode performance degradation under critical operating conditions, establishing Ni depletion, porosity increase and a tripe phase boundary density decrease in the anode functional layer. It is shown that short-term sulfur poisoning behavior can be used to assess long-term stability.

Nickel (Ni) - gadolinium doped ceria (GDC) is one of the promising anode materials for solid oxide fuel cells (SOFCs). However, they are not as stable as Ni - yttria-stabilized zirconia (YSZ) anodes at reducing atmosphere, since both Ni and GDC migrate and porous microstructure changes. The degradation behavior of the Ni-GDC anode is thus more complex than that of Ni-YSZ. In the present study, novel operando observations of the morphological changes of patterned Ni on a GDC substrate as well as conventional ex-situ measurements are conducted under SOFC operation. Both Ni and GDC moved dynamically in the range of several tens of microns during 51 h operation, where the three phase boundary (TPB) length dynamically changed during the operation. Nano-size GDC particles appeared on the Ni surface and the GDC surface was strongly roughened, which were the distinctive morphological changes of the patterned Ni-GDC anode.

In this work, nickel and gadolinium-doped ceria (GDC)-infiltrated lanthanum strontium titanate (LST) anodes are fabricated, and their electrode performances under a hydrogen atmosphere is investigated in terms of the Ni:GDC ratios and cell operating temperature. The Ni/GDC-infiltrated LST anode exhibits excellent electrode performance in comparison with the Ni- or GDC-infiltrated anodes, which is attributed to the synergistic effect of an extended triple-phase boundary length by GDC and good catalytic activity for hydrogen oxidation because of the Ni particles. The polarization resistances (Rp) of Ni/GDC-infiltrated LST are 0.07, 0.08, and 0.12 Ω cm2 at 800, 750, and 700 °C, respectively, which are approximately three orders of magnitude lower than that of the LST anode (68.5 Ω cm2 at 700 °C). The effect of Ni and GDC on the electrochemical performance of LST was also investigated by using electrochemical impedance spectroscopy (EIS). The anode polarization resistance (Rp) is confirmed to be dependent on the content and dispersion state (microstructure) of the Ni and GDC nanoparticles.

International audience; This paper reports the study of the densification of 20% Gd doped ceria (Ce0.8Gd0.2O1.9 (GDC)) interlayers in SOFC cathodes through two different routes: the well-known addition of sintering elements, and an innovative densification process by infiltration. First, Li, Cu, and Zn nitrates were added to GDC powders. The effect of these additives on the densification was studied by dilatometry on pellets, and show a large decrease of the sintering temperature from 1330 °C (pure GDC), down to 1080 °C, 950 °C, and 930 °C for Zn, Cu, and Li addition, respectively. However, this promising result does not apply to screen-printed layers, which are more porous than pellets and in which the shrinkage is constrained by the substrate. The second approach consists in preparing a pre-sintered GDC layer, which is subsequently infiltrated with Ce and Gd nitrates and sintered at 1250 °C to increase its density. Such an approach results in highly dense GDC interlayers. Using La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) as electrode, the influence of the interlayers on the cathode performance was studied. The addition of sintering aids dramatically increases the cell resistances, most likely because the additives increase the reactivity between GDC and either Yttria Stabilized Zirconia (YSZ) or LSCF, thus losing the expected benefit related to the decrease of sintering temperatures. The interlayers prepared by infiltration do not induce additional resistances in the cell, which results in power densities of single cells 40–50% higher than those of cells prepared with commercial GDC interlayers, making this approach a valuable alternative to sintering aids.

In this study, we report a high performance and redox-stable symmetrical solid oxide fuel cell (SOFC) based on (Ba0.5Sr0.5) (Mo0.1Fe0.9)O3-δ (BSMF) electrode and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. BSMF is able to operate both as anode and cathode. Excellent electrocatalytic activity has been achieved on BSMF towards hydrogen oxidation and oxygen reduction. Due to its closely matched lattice parameter to LSGM electrolyte, a unique diffuse interface is formed between BSMF and LSGM. Compared to a clean interface, e.g. BSMF/gadolinium doped ceria interface, this diffuse interface promotes the performance of BSMF electrode 1–1.8 times in 600–800 °C. Polarization resistance of the BSMF/LSGM specimen is as low as 0.047 and 0.007 Ωcm2 in humidified H2 and in air at 800 °C, respectively. On the BSMF/LSGM/BSMF symmetrical cell, a maximum power density of 2.28 W/cm2 is achieved at 800 °C, the highest among with redox-stable ceramic electrodes to the best of our knowledge. Redox stability of this cell is confirmed. The role of anode and cathode is reversed back and forth in different operation modes. No apparent degradation is observed through 4 cycles within a 110 h operation period. These findings demonstrate that (Ba0.5Sr0.5) (Mo0.1Fe0.9)O3-δ coupled with LSGM electrolyte is an excellent choice to build a high performance, redox-stable SOFC.

Microstructures of porous electrodes have great importance for promoting electrochemical reactions in solid oxide fuel cells (SOFCs). The present paper describes the application of isostatic pressing of screen printed nickel (Ni) gadolinium doped ceria (GDC) composite anode slurry on an electrolyte supported cell (ESC) and quantitatively discusses its influence on the cell electrochemical performance and microstructure. The current-voltage characteristics and electrochemical impedance spectra of the fabricated anodes of the ESC are measured. The microstructure parameters of the anodes are obtained by focused ion beam-scanning electron microscopy (FIB-SEM). The isostatic pressing decreases the porosity of the screen printed anodes, improves the Ni connectivity and increases the active triple phase boundary (TPB) density, but it does not change significantly the total TPB and double phase boundary (DPB) densities. Additionally, pressing enhances the adhesion of the electrode to the electrolyte. These observations are consistent with the improvement of the electrochemical performance of the isostatically pressed anodes.

Functionally graded composite interlayer based on 50% of La 0.54 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ and 50% of La 0.54 Sr 0.4 Fe 0.2 Co 0.8 O 3-δ (CF-1) and cobalt and gadolinium doped ceria (CoCGO) is synthesized varying the mass ratio as CF-1:CoCGO = 80:20(L80-C20), 50:50(L50-C50) and 20:80(L20-C80). Detail study using impedance spectroscopy of symmetrical cell fabricated with CoCGO as electrolyte reveals the lowest electrode polarization 0.04 Ω cm 2 at 800 °C for L80-C20 composite. Electrode and ohmic polarization is also evaluated configuring the symmetric cell as CF-1/L80-C20||CoCGO||L80-C20/CF-1. Symmetric cell with varying composition of the composite interlayer (L80-C20/L50-C50/L20-C80||CoCGO||L20-C80/L50-C50/L80-C20) shows considerably low electrode polarization of 0.067 Ω cm 2 at 800 °C with activation energy 1.19 eV. Electrochemical performances evaluated using single cell configuration Ni-YSZ||YSZ||CoCGO/L20-C80/L50-C50/L80-C20/CF-1 shows power density as high as 2.03 W cm −2 at 800 °C at 0.7 V. Addition of composite interlayers increases the stability significantly and the voltage degradation is found negligible (0.9%) for first 300 h at a constant load of 0.5 A cm −2 which is further increased to 2.9% for next 300 h. The cell stability is clinically correlated with layer wise elemental ‘Sr’ mapping in the applied quad interlayers.

Gadolinium doped ceria (CGO) is a commonly used electrolytic material for Solid Oxide Fuel Cells (SOFCs) and for this reason different shaping methods for its deposition are reported in literature. Most of these processes are based on the use of organic-based CGO suspensions, but water-based processes are acquiring increasingly interest for their economical and environmental friendly properties. In this paper we reported how the components of water-based suspension and some unexpected process parameters can deeply affect the functional properties of the final powder. In particular, we observed that CGO powders are strongly affected by ionic leaching induced by furoic acid used as dispersant: the extent of this leaching was related to the dispersant concentration and suspension’s ball-milling-time; the phenomenon was confirmed by ICP-AES analyses on suspensions surnatant. Most importantly, ionic leaching affected the electrical properties of CGO: leached powder showed a higher ionic conductivity as a consequence of a partial removal of Gd ions at the grain boundaries. This work is therefore pointing out that when considering water-based suspensions, it is extremely important to carefully consider all the process parameters, including the organic components of the ceramic suspension, as these could lead to unexpected effects on the properties of the powder, affecting the performance of the final shaped material.

In the present study, multiscale microstructure evolutions of nickel and gadolinium doped ceria (Ni-GDC) composite anode operated under humidified condition (800 °C, 40%H2O:20%H2:40%N2) are investigated. Focused ion beam - scanning electron microscopy (FIB-SEM) with spatial resolutions of 2 nm and 25 nm are used to observe the changes in both local and whole microstructures. Significant multiscale reorganization of the microstructure is observed in both Ni and GDC phases. Migration of GDC nano-particles in the range of several micrometers is confirmed. In addition, thin GDC layer with nanometer thickness is formed on the Ni surface, similar to the strong metal support interaction (SMSI). Heterogeneous microstructural evolutions of the GDC phase are seen at the electrode-electrolyte interface and at the vicinity of the current collector. The GDC microstructural evolution is considered as a key factor of anode degradation.

The electrochemical impedance response of an electrolyte supported Solid Oxide Fuel Cell (SOFC) was studied for different compositions of feed in the anode compartment. The cell was composed of Yttria Stabilized Zirconia (YSZ), as electrolyte, and commercial Nickel/Gadolinium doped Ceria (Ni/GDC) cermet and Lanthanum Strontium Manganite (LSM), as anode and cathode electrodes, respectively. The impedance responses of the anode and cathode were deconvoluted using the analysis method of differences in the impedance spectra (ADIS). This allowed focusing on the electrochemical processes, which occur at the anode electrode and analyzing them adequately via equivalent electric circuit modelling. The main finding is that the Ni/GDC anode electrode exhibits a Gerischer impedance response, characteristic of chemical and electrochemical competing processes, which was associated with the formation of OH ad − on GDC oxygen vacancies as the prevailing intermediate species for the electro-oxidation of H2 on Ni/GDC anode. It is shown that H2O plays a dominant role for the formation of the OH ad − species on the GDC surface through its reaction with O2−, thus contributing autocatalytically on the promotion of H2 electro-oxidation on Ni/GDC anode.

International audience; This paper is devoted to the study of composite cathodes of La2NiO4+δ infiltrated into a Gd-doped ceria backbone. Porous Gd-doped ceria backbones are screen printed onto yttria-stabilized zirconia or Gd-doped ceria dense electrolytes, and infiltrated with a La and Ni nitrate solution (2:1 stoichiometry ratio). The influence of the preparation parameters on the polarization resistance, such as the concentration of the infiltration solution, the amount of infiltrated phase, the annealing temperature, the thickness of the electrode, and the nature of the electrolyte, is characterized by impedance spectroscopy performed on symmetrical cells. The optimization of these parameters results in a decrease of the polarization resistance down to 0.15 Ω cm2 at 600 °C. Using the Adler-Lane-Steele model, the modelling of the impedance diagrams leads to the determination of the ionic conductivity as well as the surface exchange rate of the infiltrated electrode.

Infiltration of nickel nanoparticles into nickel – yttria-stabilized-zirconia (Ni-YSZ) cermet anodes improves anode performance by reducing the average nickel feature size of the electrode, thus increasing the density of triple phase boundaries (TPBs). However, the TPBs of nickel nanoparticles are not fully utilized because there is no conductive pathway between nanoparticles, and nickel nanoparticles suffer from rapid coarsening during operation. This work explores the infiltration of Gd0.1Ce0.9O2-δ (GDC) as a material for connecting and stabilizing infiltrated nickel nanoparticles. Anodes were infiltrated with Ni, GDC, and Ni-GDC to study their stability and electrochemical performance. Measurements show that the simultaneous infiltration of nickel and GDC results in a greater performance improvement than either nickel or GDC alone. From this result, it is speculated that GDC provides a conducting pathway between nickel nanoparticles, better utilizing their TPBs. Fitting of electrochemical impedance spectra with an equivalent circuit model is used to measure individual cell resistances, revealing that infiltration of GDC reduces the activation energy of the anodic charge transfer reaction from 1.29 eV to 0.74 eV. The Ni-GDC nanoparticles are also more durable than nickel nanoparticles, demonstrating microstructural stability after 120 h of constant current at 800 °C, while nickel alone shows extensive coarsening.

Nanocrystalline single phase La1-xSrxCo1-yFeyO3-delta LSCF] (0 < x

Mixed ionic electronic conducting praseodymium and gadolinium doped ceria (Pr x Ce 0.95− x Gd 0.05 O 2− δ (0.15 ≤ x ≤ 0.40)) compositions have been studied as a cathode material for low temperature solid oxide fuel cells. Four compositions of Pr x Ce 0.95− x Gd 0.05 O 2− δ (PCGO) have been prepared by varying the praseodymium content. Phase formation, thermal expansion, ionic conductivity, electronic conductivity, ionic transference number and electrochemical performance have been investigated. X-ray diffraction results indicate that PCGO samples crystallize in the fluorite structure, and the lattice volume decreases with increasing praseodymium content, x . The coefficient of thermal expansion increases with increasing x , and at x = 0.2 shows an optimum value of 12 × 10 −6 K −1 . Ionic transference number decrease while electronic conductivity increase with increasing x . It has been found that electronic contribution to the total conductivity is higher than ionic contribution for all compositions. The praseodymium doping with cerium dioxide introduces impurity bands within the ceria band gap and facilitates the electronic transition from valance band to conduction band through praseodymium impurity levels. The single cell with configuration, Pr 0.2 Ce 0.75− x Gd 0.05 O 2− δ –Ce 0.80 Gd 0.20 O 2− δ ∥Ce 0.80 Gd 0.20 O 2− δ ∥NiO–Ce 0.80 Gd 0.20 O 2− δ delivers a maximum power density of 98 mW cm −2 at 650 °C.

Cermet compositions based on Nickel–Copper alloys with gadolinium doped ceria as the ceramic matrix, Ni1-xCuxO (x = 0, 0.4 and 0.8 mol%) with 50 wt% CGO (Ce0.9Gd0.1O1.95), are assessed as possible anodes for SOFCs operating in H2 and biogas fuels. Equivalent circuit modelling is employed to evaluate the total polarisation resistance of cermet anodes with correction of data for electronic short-circuiting that may arise when using Ce0.9Gd0.1O1.95 (CGO) electrolytes under reducing conditions. Data analysis highlights that presence of electronic leakage in CGO electrolyte can lead to severe underestimation of total polarisation resistance in the case of H2 fuel, with this deviation becoming more serious with increasing temperature. In contrast, less significant effects are noted under biogas in similar conditions, due to a less reducing nature of this fuel. The results underscore that anode characteristics are highly dependent on the effective oxygen partial pressure of working gas atmosphere and that suitable correction of data is imperative before discussion. Corrected values for polarisation resistance in each fuel reveal the Nickel–Copper alloy cermet with copper content of x = 0.4 to be beneficial under the biogas atmosphere, while, conversely, the pure Ni-cermet is shown to be the peak performing composition in H2 fuel.

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is a promising cathode material for solid oxide fuel cells due to its high oxygen reduction reaction (ORR) activity. A gadolinium-doped ceria (GDC) barrier layer is essential to preventing side reactions between LSCF and an yttrium-stabilized zirconia (YSZ) electrolyte. However, several challenges are associated with the coating of GDC barrier layer on the YSZ electrolyte, including delamination of the GDC layer due to sinterability differences and formation of an insulating layer at a high annealing temperature. In this study, we describe a structure for a newly designed interfacial layer consisting of a GDC barrier layer and a nano-web–structured LSCF thin-film layer (NW-LSCF) through a facile spin-coating method. A dense GDC barrier layer with a thickness of approximately 400 nm was successfully applied to the surface of a YSZ electrolyte without delamination at a low annealing temperature. The high surface area of the NW-LSCF enhanced ORR due to an increased triple-phase boundary length. Cells employing a GDC barrier layer and NW-LSCF interlayer exhibited improved electrochemical performance. Peak power density reached 1.29 W/cm2 at an operating temperature of 550 °C and 2.14 W/cm2 at 650 °C.

The allowable tar content in gasification syngas is one of the key questions for the exploitation of the full potential of fuel cell concepts with integrated gasification systems. A better understanding of the interaction between tars and the SOFC anodes which leads to carbon formation and deposition is needed in order to design systems where the extent of gas cleaning operations is minimized. Model tar compounds (toluene, benzene, naphthalene) have been used in experimental studies to represent those arising from biomass/coal gasification. However, the use of toluene as a model tar overestimates the negative impact of a real gasification tar on SOFC anode degradation associated with carbon formation. In the present work, the effect of a gasification tar and its distillation fractions on two commercially available fuel cell anodes, Ni/YSZ (yttria stabilized zirconia) and Ni/CGO (gadolinium doped ceria), is reported. A higher impact of the lighter tar fractions was observed, in terms of more carbon formation on the anodes, in comparison with the whole tar sample. The characterization of the recovered tars after contact with the anode materials revealed a shift towards a heavier molecular weight distribution, reinforcing the view that these fractions have reacted on the anode.

A novel bulk acoustic wave (BAW) microgravimetric sensor based on gallium orthophosphate is demonstrated that it is capable of operation at high temperature (up to 900 °C). The sensor is applied to the detection of carbon deposition onto electrodeposited nickel from dry methane at 600 °C and used as an analogue for studying the coking of solid oxide fuel cell (SOFC) anodes. The degradation of electrochemical performance due to deposition of carbon onto symmetrical SOFCs with nickel/gadolinium doped ceria electrodes is measured using electrochemical impedance spectroscopy (EIS). Direct correlation is observed between the frequency shift of the sensor and the change in resistance to charge transfer of the SOFC anode. An induction period (∼2 h) following exposure to methane is observed where no significant carbon deposition occurs.

Nanocrystalline La0.6Sr0.4CoO3−δ (LSC) powder with an ultrafine microstructure is synthesized via salt-assisted spray pyrolysis and subsequently stabilized in water-based dispersions. Nanoparticulate cathode thin films of LSC and LSC–GDC (gadolinium doped ceria) nanocomposites (with 10–40 wt% of GDC) are prepared via single step spin coating on yttria stabilized zirconia (YSZ) substrates. In order to prevent the chemical reaction between the cathode and the electrolyte, a thin buffer layer of GDC is deposited using spin coating on the YSZ substrates. The electrochemical performance of the thin film cathodes is measured by impedance spectroscopy on symmetrical cells in the temperature range of 450–650 °C. LSC cathode thin films (250 nm thick) with 30 wt% GDC content exhibit the lowest area specific resistance (ASR) values of 0.32, 0.78 and 2.04 Ω cm2 in ambient air at 650, 600 and 550 °C, respectively.

The oxidation resistance of the Fe-Cr alloy backbone structure of metal supported solid oxide fuel cells is significantly improved when infiltrated with gadolinium doped ceria (CGO) particles. The mechanism for the improved oxidation behaviour is elucidated using various analytical transmission electron microscopy (TEM) techniques including energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy of focus ion beamed TEM samples. The infiltrated CGO is predominately converted into CeFeO3 after high temperature processing, protecting the alloy. A thin layer of Cr-oxide is observed to be sandwiched between the CeFeO3/CGO layers and the Fe-Cr alloy particles. Despite the improved oxidation resistance at open circuit voltage, during fuel cell testing accelerated oxidation is observed at the triple phase boundaries. (C) 2012 Elsevier B.V. All rights reserved.

Major operating challenges remain to safely operate methane fuelled solid oxide fuel cells due to undesirable temperature gradients across the porous anode and carbon deposition. This article presents an experimental study on methane steam reforming (MSR) global kinetics for single operating SOFCs with Ni-GDC (gadolinium doped ceria) anodes for low steam to carbon (S/C) ratios and moderate current densities. The study points out the hitherto insufficient research on MSR global and intrinsic kinetics for operating SOFCs with complete Ni-ceria anodes. Further, it emphasizes the need to develop readily applicable global kinetic models as a subsequent step from previously reported state-of-art and complex intrinsic models. Two rate expressions of the Power law (PL) and Langmuir-Hinshelwood (LH) type have been compared and based on the analysis, limitations of using previously proposed rate expressions for Ni catalytic beds to study MSR kinetics for complete cermet anodes have been identified. Firstly, it has been shown that methane reforming on metallic (Ni) current collectors may not be always negligible, contrary to literature reports. Both PL and LH kinetic models predict significantly different local MSR reaction rate and species partial pressure distributions along the normalized reactor length, indicating a strong need for further experimental verifications.

We have performed cation diffusion experiments within the framework of the evaluation of long-term stability of gadolinium doped ceria acting as a reaction barrier between cathode and electrolyte materials. Diffusion couples were prepared depositing La0.8Sr0.2Co0.2Fe0.8OX (LSCF) thick films onto sintered Ce0.9Gd0.1O1.95 (GDC) substrates by Pulse Laser Deposition (PLD). Interdiffusion across the LSCF/GDC interface was investigated by means of SIMS, at temperatures of 1000–1200 °C and times from 30 h up to 672 h. A significant diffusion of lanthanum into GDC and diffusion of cerium and gadolinium into LSCF were observed. In contrast, only shallow depth profiles for strontium, iron and cobalt into GDC were observed. X-ray diffraction (XRD) reveals the probable formation of lanthanum doped ceria (LDC) in the vicinity of the interface. Finally, the temperature dependence of lanthanum and strontium diffusion coefficients in bulk GDC is described by the following equations in the temperature range indicated: La in GDC : D b u l k / m 2 s − 1 = 4.2 × 10 − 5 exp − 390 kJ mol − 1 R T ( 1273 − 1473 K ) ; Sr in GDC : D b u l k / m 2 s − 1 = 1.1 × 10 − 7 exp − 320 kJ mol − 1 R T ( 1373 − 1473 K ) . The grain boundary diffusion of lanthanum is, at least, five orders of magnitude faster than the bulk diffusion.

The combination of biomass gasification with solid oxide fuel cells (SOFCs) is gaining increasing interest as an efficient and environmentally benign method of producing electricity and heat. However, tars in the gas stream arising from the gasification of biomass material can deposit carbon on the SOFC anode, having detrimental effects to the life cycle and operational characteristics of the fuel cell. This work examines the impact of biomass gasification syngas components combined with benzene as a model tar, on carbon formation on Ni/CGO (gadolinium-doped ceria) SOFC anodes. Thermodynamic calculations suggest that SOFCs operating at temperatures > 750 °C are not susceptible to carbon deposition from a typical biomass gasification syngas containing 15 g m −3 benzene. However, intermediate temperature SOFCs operating at temperatures −3 benzene at 765 °C for 3 h at a current density of 300 mA cm −2 , with negligible impact on the electrochemical performance of the anode. Furthermore, no carbon could be detected on the anode at this current density when benzene levels were −3 .

Single-chamber fuel cells with electrodes supported on an electrolyte of gadolinium doped ceria Ce1−xGdxO2−y with x = 0.2 (CGO) 200 μm thickness has been successfully prepared and characterized. The cells were fed directly with a mixture of methane and air. Doped ceria electrolyte supports were prepared from powders obtained by the acetyl-acetonate sol–gel related method. Inks prepared from mixtures of precursor powders of NiO and CGO with different particle sizes and compositions were prepared, analysed and used to obtain optimal porous anodes thick films. Cathodes based on La0.5Sr0.5CoO3 perovskites (LSCO) were also prepared and deposited on the other side of the electrolyte by inks prepared with a mixture of powders of LSCO, CGO and AgO obtained also by sol–gel related techniques. Both electrodes were deposited by dip coating at different thicknesses (20–30 μm) using a commercial resin where the electrode powders were dispersed. Finally, electrical properties were determined in a single-chamber reactor where methane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Temperature, composition and flux rate values of the carrier gas were determinants for the optimization of the electrical properties of the fuel cells.

Nanocrystalline powders of CGO materials with different contents of Gd were prepared by a freeze-drying method and used to prepare dense ceramic samples. This method allowed one to obtain good quality samples to re-examine the reducibility of CGO materials. These materials were characterized by a combination of coulometric titration, impedance spectroscopy and ion blocking measurements to evaluate changes in point defect chemistry and mixed conducting properties. We have examined the onset of n-type conductivity as a function of temperature and oxygen partial pressure, and this information was used to re-examine the mixed transport properties in reducing conditions imposed by fuels, and also the OCV obtained with CGO solid electrolyte cells under air/CGO/fuel gradients. The polaron mobility was also evaluated and was found to depend slightly on temperature and to decrease with increasing oxygen deficiency. This confirmed that the electronic conductivity is mainly dependent on reducibility.

The utilization of anode-supported electrolytes is a useful strategy to increase the electrical properties of the solid oxide fuel cells, because it is possible to decrease considerably the thickness of the electrolytes. We have successfully prepared single-chamber fuel cells of gadolinium doped ceria electrolytes Ce 1− x Gd x O 2− y (CGO) supported on an anode formed by a cermet of NiO/CGO. Mixtures of precursor powders of NiO and gadolinium doped ceria with different particle sizes and compositions were analysed to obtain optimal bulk porous anodes to be used as anode-supported fuel cells. Doped ceria electrolytes were prepared by sol–gel related techniques. Then, ceria-based electrolytes were deposited by dip coating at different thicknesses (15–30 μm) using an ink prepared with nanometric powders of electrolytes dispersed in a liquid polymer. Cathodes of La 1− x Sr x CoO 3 (LSCO) were also prepared by sol–gel related techniques and were deposited on the electrolyte thick films. Finally, electrical properties were determined in a single-chamber reactor where propane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Flux rate values of the carrier gas and propane partial pressure were determinants for the optimization of the electrical properties of the fuel cells.

The application of infrared thermal imaging to the study of solid oxide fuel cells is demonstrated. The temperature increase accompanying polarisation of gadolinium doped ceria pellet cells is measured and the effect of temperature increase on polarisation characteristics is modelled. Temperature increases of the order of 2.5 °C were measured for heavily loaded pellet cells. Measurement accuracy of 0.1 °C and spatial resolution of 0.5 mm allow temperature distribution heterogeneity to be clearly discerned. A total heat transfer coefficient is derived from experimental results that allow the development of a model that predicts the extent of self-heating. For pellet fuel cells, self-heating is not expected to have a large effect on the polarisation characteristics; however, for thin electrolytes and high current density the effect becomes appreciable.

This paper considers fuel cell research from a new point of view, describing so called non-conventional systems including intermediate temperature and new concept fuel cells based on recent developments of materials and systems.