Low temperature prepared (La0.8Sr0.2)0.9MnO3-δ-Y0.15Zr0.85O1.93 (LSM-YSZ) nano-composite cathode has high three-phase boundary (TPB) density and shows higher oxygen reduction reaction (ORR) activity than traditional LSM-YSZ cathode at reduced temperatures. But the weak connection between cathode and electrolyte due to low sintering temperature restrains the performance of LSM-YSZ nano-composite cathode. A YSZ interlayer, consisted of nanoparticles smaller than 10 nm, is introduced by spinning coating hydrolyzed YSZ sol solution on electrolyte and sintering at 800 °C. The thickness of the interlayer is about 150 nm. The YSZ interlayer intimately adheres to the electrolyte and shows obvious agglomeration with LSM-YSZ nano-composite cathode. The power densities of the cell with interlayer are 0.83, 0.46 and 0.21 W/cm2 under 0.7 V at 800, 700 and 600 °C, respectively, which are 36%, 48% and 50% improved than that of original cell. The interlayer introduction slightly increases the ohmic resistance but significantly decreases the polarization resistance. The depressed high frequency arcs of impedance spectra suggest that the oxygen incorporation kinetics are enhanced at the boundary of YSZ interlayer and LSM-YSZ nano-composite cathode, contributing to improved electrochemical performance of the cell with interlayer.Download high-res image (151KB)Download full-size imageA YSZ interlayer prepared with hydrolyzed YSZ sol solution effectively improved the performance of low temperature prepared LSM-YSZ nano-composite cathode.

•YSB-LSM composite is co-synthesized via a citric-nitrate combustion method.•Oxygen evolution is significantly enhanced on YSB-LSM composite.•SOEC with YSB-LSM composite anode achieves −1.52 A cm−2 at 800 °C and 1.28 V.•YSB-LSM composite anode shows low Ea value for oxygen evolution reaction.In this study we report a nano-composite anode comprised of Y-stabilized Bi2O3 (YSB) and Sr-substituted LaMnO3 (LSM) for solid oxide electrolysis cell (SOEC). The composite powder with primary particle size ranging from 20 to 80 nm is co-synthesized via a simple citric-nitrate combustion method. X-ray diffraction examination confirms cubic fluorite YSB and rhombohedral perovskite LSM as the main phases in the composite. Temperature programmed O2 desorption identifies remarkable low temperature desorption at 330 °C. Similarly, temperature programmed H2 reduction reveals strong reduction at 385 °C. The facile oxygen evolution on YSB-LSM may result from the increased amount of oxygen vacancies and improved oxygen ion mobility. A cell employing YSB-LSM composite anode achieves current density of −1.52 A cm−2 at 800 °C and 1.28 V, 50% higher than conventional LSM-YSZ cell. Impedance results and analysis of distribution of relaxation times indicate that the rate-determining anode processes are effectively accelerated on YSB-LSM. The activation energy for oxygen evolution reaction on YSB-LSM is reduced to 0.65 eV, notably lower than on LSM-YSZ (1.29 eV). The high performance of YSB-LSM composite anode is attributed to the fast ion decorporation on YSB, the facile O2 formation on LSM, and the abundant phase boundaries that facilitate the two processes.

•Bi-structured gadolinia doped ceria (GDC) interlayer for solid oxide fuel cell.•Bi-structured GDC interlayer deposited by sputtering.•Bi-structured GDC interlayer reduces 38.4% polarization resistance at 600 °C.•Bi-structured GDC interlayer raises 50.0% cell performance at 600 °C.A bi-structured gadolinia doped ceria (GDC) interlayer, which has a dense layer combining tightly with yttria-stabilized zirconia (YSZ) film and a porous layer with rough surface for contacting closely with the cathode, is prepared from a two-step sputtering process. Compared to the cell with a dense GDC interlayer, the single cell with the bi-structured GDC interlayer depicts greatly reduced ohmic and polarization resistances and increased electrochemical performance.

Doped ceria is commonly used to promote the performance of solid oxide fuel cells (SOFCs) with a lanthanum strontium manganite (LSM) cathode, but the oxygen reduction reaction (ORR) activity on the interface between LSM and doped ceria is not conclusive due to the complexity of the cathode and problematic analysis of the impedance spectra. Here, to elucidate the role of the LSM|GDC interface in the ORR, we constructed a simple LSM|GDC interface and analyzed the impedance data using a method based on the calculation of the distribution function of relaxation times (DRT). DRT analysis demonstrates that the ORR on the LSM|GDC interface possesses similar activation energies for oxygen dissociation and the subsequent oxygen atom reduction but involves an easier oxygen incorporation process in comparison with the LSM|YSZ interface. Addition of the GDC interlayer causes a decrease in cell performance because poor LSM|GDC interfaces lead to depressed dominant electrode processes of oxygen dissociation and the subsequent oxygen atom reduction. These results provide useful insight into the ORR on the LSM|GDC interface, favoring the design of a high-performance doped ceria-enhanced LSM cathode.

We for the first time have synthesized Ag/ZrO2 nanocomposites from silver mirror reaction in toluene, which refers to the reduction of silver–dodecylamine complexes by acetaldehyde (CH3CHO) in the presence of ZrO2 nanocrystals. The obtained nanocomposites show excellent catalytic activity in the successive reduction of p-nitrophenol (4-NP) by NaBH4.

•LSM–YSZ composite is co-synthesized by citrate-nitrate combustion method.•Co-synthesized LSM–YSZ cathode exhibits well distributed and intimately connected nanoparticles of LSM and YSZ.•Cell with co-synthesized LSM–YSZ cathode outputs high current density at 600 °C.•Co-synthesized LSM–YSZ cathode shows good stability at 800 °C.(La0.8Sr0.2)0.9MnO3Y0.15Zr0.85O2 (LSM–YSZ) composite co-synthesized by citrate-nitrate combustion method are investigated for solid oxide fuel cell cathode. The co-synthesized LSM–YSZ composite powders are characterized by XRD, HR-SEM, TEM, HR-TEM and EDX analysis. The phase separation of the precursor into LSM perovskite and YSZ fluorite occurs at temperatures above 900 °C, about 200 °C higher than the formation temperature of pure LSM or pure YSZ. In the nano-sheets of LSM–YSZ composite, nano-particles of LSM and YSZ are well distributed and intimately contacted with each other. The nanostructures remain in the co-synthesized LSM–YSZ cathode. The co-synthesized LSM–YSZ cathode improves oxygen reduction reaction (ORR) activity, especially at reduced operation temperature. The cell with co-synthesized LSM–YSZ cathode delivers current density 150% times of the cell with traditional LSM–YSZ cathode at 600 °C. Electrochemical impedance spectra (EIS) analysis shows that oxygen reduction reaction is accelerated due to high three phase boundary (TPB) density. The co-synthesized LSM–YSZ cathode shows good stability under cell operation at 800 °C.

Reluctant oxygen-reduction-reaction (ORR) activity has been a long-standing challenge limiting cell performance for solid oxide fuel cells (SOFCs) in both centralized and distributed power applications. We report here that this challenge has been tackled with coloading of (La,Sr)MnO3 (LSM) and Y2O3 stabilized zirconia (YSZ) nanoparticles within a porous YSZ framework. This design dramatically improves ORR activity, enhances fuel cell output (200–300% power improvement), and enables superior stability (no observed degradation within 500 h of operation) from 600 to 800 °C. The improved performance is attributed to the intimate contacts between nanoparticulate YSZ and LSM particles in the three-phase boundaries in the cathode.

•Interlayer-free LSCF-CZ electrode is developed on YSZ.•CZ impedes the reaction between cathode and YSZ electrolyte.•Incorporation of oxygen ions from LSCF-CZ cathode into electrolyte is accelerated.•LSCF-CZ cathode shows high electrochemical stability.Interlayer-free La0.6Sr0.4Co0.2Fe0.8O3−δ-Ce0.8Zr0.2O2−δ (LSCF-CZ) composite cathode on YSZ electrolyte has been studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectra (EIS). The addition of CZ suppresses the formation of non-conductive SrZrO3 at the cathode and YSZ electrolyte interface. As a result, the LSCF-CZ cell performance is greatly elevated. The LSCF-CZ cell exhibits 8.7 times higher current density than the LSCF cell at 0.8 V and 600 °C. The incorporation of oxygen anion from LSCF-CZ cathode into YSZ electrolyte is significantly accelerated. The stability of the LSCF-CZ cathode is remarkably improved as compared with the LSCF cathode at 600 °C.Ce0.8Zr0.2O2−δ-La0.6Sr0.4Co0.2Fe0.8O3−δ (CZ-LSCF) composite cathode on YSZ electrolyte displays excellent electrochemical performance and high stability.

•Co1.5Mn1.5O4 nano-particles are infiltrated into the LSM-YSZ cathodes.•The DRT method is used to analyze the EIS results.•The ORR is greatly accelerated by the CMO particles at TPBs.Solid oxide fuel cells with nano-sized Co1.5Mn1.5O4 (CMO) crystals infiltrated LSM-YSZ cathodes have been investigated using XRD, SEM, EIS and cell performance measurements. 20∼30 nm nanocrystals of Co1.5Mn1.5O4 are present on the surfaces of LSM and YSZ particles. The infiltrated cells display more than 2 times higher power density than the non-infiltrated cell under 0.7 V at the same temperature in 600–700 °C. The Co1.5Mn1.5O4 infiltration reduces both ohmic resistance and polarization resistance in the cells. The distribution of relaxation times (DRT) analysis of the EIS data depicts that oxygen reduction process is greatly accelerated on the infiltrated cathode, which is attributed to high catalytic activity of nano-sized CMO crystals.

•Cell area specific resistance was current-dependent during high temperature CO2 reduction.•Ni–YSZ electrode showed higher resistance in SOEC mode than SOFC mode.•The temperature drop at thermal minimum voltage created the condition for coking on Ni–YSZ.•Higher temperature and higher CO2 partial pressure could help minimize coking on Ni–YSZ.Electrochemical reduction of carbon dioxide in the intermediate temperature region was investigated by utilizing a reversible solid oxide electrolysis cell (SOEC). The current–potential (i–V) curve exhibited a nonlinear characteristic at low current density. Differentiation of i–V curves revealed that the cell area specific resistance (ASR) was current-dependent and had its maximum in electrolysis mode and minimum in fuel cell mode. Impedance measurements were performed under different current densities and gas compositions, and the results were analyzed by calculating the distribution of relaxation times. The ASR variation resulted from the difference in electrochemical reactions occurring on the Ni–YSZ electrode, i.e., Ni–YSZ is a better electrode for CO oxidation than for CO2 reduction. Coke formation on Ni–YSZ played a crucial role in affecting its electrolysis performance in the intermediate temperature region. The ASR apex was associated with a decrease in cell temperature during electrolysis due to the endothermic nature of CO2 reduction reaction. It was postulated that such a decrease in temperature and rise in CO concentration led to coke formation. As a consequence, higher temperature (>700 °C), higher CO2 concentration (>50%), and the presence of hydrogen or steam are recommended for efficient CO2 reduction in solid oxide electrochemical cells.

The YSZ electrolyte fuel cell with a ternary cathode composed of LSM–YSZ–Ce0.9Mn0.1O2−δ exhibits ca. 2.6 times higher current density than that with a binary cathode composed of LSM–YSZ at 600 °C.

The effects and affecting mechanisms of carbon dioxide on oxygen reduction reactions on the La0.6Sr0.4CoO3−δ (LSC) and La0.8Sr0.2MnO3+δ (LSM) cathodes have been investigated. The presence of CO2 in O2 flow reduces the LSC and LSM cell performance and increases polarization resistance. CO2 impedes oxygen dissociative adsorption on the LSC cathode, whereas CO2 inhibits dissociation of adsorbed oxygen molecule or diffusion of O-species on the LSM cathode. CO2 adsorption on the LSC cathode obeys Temkin model in 550–650 °C and Freundlich model in 700–800 °C. Different CO2 adsorption behaviors are ascribed to the change in LSC structure and the change in oxygen reduction mechanism. CO2 adsorption on the LSM cathode obeys Freundlich model in 650–800 °C. The differences in the effects and affecting mechanisms of CO2 on LSM and LSC are related to their differences in composition and structure.Graphical abstractCO2 adsorption on LSC cathode obeys Temkin models in the temperature range of 550–650 °C, whereas CO2 adsorption on LSM cathode obeys Freundlich model in the temperature range of 650–800 °C.Highlights► Effects of carbon dioxide on performances and EIS of La0.6Sr0.4CoO3−δ (LSC) cathode. ► Effects of carbon dioxide on performances and EIS of La0.8Sr0.2MnO3−δ (LSM) cathode. ► CO2 adsorption model on LSC from 550 °C to 800 °C. ► CO2 adsorption model on LSM from 650 °C to 800 °C.

•Electrochemical stability of LSCF against CO2 and H2O at high and low temperature.•Chemical stability of LSCF against CO2 and H2O at high and low temperature.•Formation of surface carbonates and SrCO3 phases on LSCF.•Degradation mechanism of LSCF cathode.•Role of H2O in the poisoning effect of CO2.High- and low- temperature behaviors of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode for solid oxide fuel cells operating under CO2/H2O-containing atmosphere are investigated. LSCF shows different stability against CO2 and H2O at high and low temperature. LSCF has excellent electrochemical performance and high stability against the corrosion of CO2 and H2O at 750 °C due to weak reactivity of LSCF with CO2. LSCF shows a serious degradation at 600 °C under operation with O2–CO2(2.83%)–H2O(2.64%), which is ascribed to the impeded oxygen activation and oxygen surface diffusion by surface carbonates and SrCO3 phases on LSCF surface. Under CO2(5%)–H2O(2.81%)–He, LSCF reacts with CO2 to yield SrCO3 phases in 400–680 °C, and H2O aggravates the chemical reaction between CO2 and LSCF. Taking into account of SrCO3 phase formation on LSCF, LSCF cathode is stable under operation with O2–CO2(2.83%)–H2O(2.64%) in 680–800 °C, whereas it is unstable below 680 °C. LSCF can be subject to degradation caused by CO2 and H2O in air during long-term operation below 680 °C.LSCF shows high stability against CO2 and H2O at 750 °C but a serious degradation at 600 °C.

Series of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) samples have been prepared by modified citrate-nitrate combustion method from the precursor solutions with different pH values and citrate/metal ion ratios. The XRD results reveal that BSCF oxide free of impurity phases can be obtained from a precursor solution with a suitable pH value and a suitable C/M value, whereas CO2-TPD profiles show that there are minor carbonates species present in all BSCF samples, but the amount of these carbonates varies with the pH and C/M values of precursor solutions. The current density–voltage characteristics indicate that carbonates in the BSCF samples reduce the cell performance. The electrochemical impedance spectra (EIS) show that carbonates in BSCF lead to increases in ohmic and polarization resistances. High performance is achieved on the cell with a cathode using a pure BSCF calcined under O2 flow at 900 °C.Graphical abstractCarbonates on Ba0.5Sr0.5Co0.8Fe0.2O3−δ from preparation reduce electrochemical performance of cathode.Highlights► Ba0.5Sr0.5Co0.8Fe0.2O3−δ samples were prepared from different precursor solutions. ► Carbonates in BSCF were studied by XRD technique. ► Carbonates in BSCF were studied by CO2-TPD technique. ► Effect of carbonates on BSCF from preparation on cathode of SOFC.

The segmented-in-series solid oxide fuel cell comprising fuel channel, anode, cathode and electrolyte layers has been evaluated by developing a two-dimensional model, in which the equations have been solved numerically through finite element methods. The results indicate that the voltage of each membrane electrode assembly (MEA) exhibits a parabola-like curve and is higher than the appointed voltage of unit cell (0.7 V). From fuel inlet to outlet, the voltage of each MEA deceases due to the decreasing local H2 concentration. When both the interconnector and electrolyte gap lengths are fixed, the cell module with 5 mm long anode gives the maximal power density for the SS-SOFC. Higher power densities can be achieved through increasing the cathode thickness.

An anode-supported micro-tubular solid oxide fuel cell (SOFC) is analyzed by a two-dimensional axisymmetric numerical model, which is validated with the experimental I–V data. The temperature distribution generated by the thermo-electrochemical model is used to calculate the thermal stress field in the tubular SOFC. The results indicate that the current transport in the anode is the same at every investigated position. The stress of the micro-tubular cell occurs mainly because of the residual stress due to the mismatch between the coefficients of thermal expansion of the materials of the membrane electrode assembly. The micro-tubular cell can operate safely, but if there is an interfacial defect or a high enough tensile stress applied at the electrolyte, a failure can arise.

The oxidation of Ni–YSZ cermet as well the reduction of re-oxidized Ni–YSZ cermet was investigated by using temperature-programmed oxidation (TPO), temperature-programmed reduction (TPR) and scanning electron microscope (SEM). The scanning electron microscope (SEM) photographs and temperature-programmed reduction (TPR) profiles indicated that the sintering of smaller nickel oxide crystallites to larger aggregates occurred concurrently with the formation of smaller nickel oxide crystallites from the oxidation of nickel at 800 °C, and the sintering of smaller nickel oxide crystallites at 600 °C was slower than that at 800 °C. The SEM results showed that each Ni particle was separated into a lot of smaller NiO particles during oxidation. The TPO profiles showed that two kinds of nickel particles exist in the anode reduced at 800 and 600 °C, one with high activity towards oxidation for the nickel crystallites directly from reduction, and another one with low activity towards oxidation for the sintered nickel particles. The Ni–YSZ anodes reduced at higher temperature showed higher re-oxidation temperature than the one reduced at lower temperature because of the accelerated passivating and sintering of the smaller nickel particles at higher temperature. The re-oxidation profiles were almost unchanged during redox cycling at 600 °C, whereas the re-oxidation peak temperature decreased during redox cycling at 800 °C, indicating that the primary nickel grains split to smaller ones upon cyclic reduction at higher temperature.

Ba1−xSrxCo0.8Fe0.2O3−δ (BSCF)(0 ≤ x ≤ 1) composite oxides were prepared and tested as cathodes for low-temperature solid oxide fuel cells (SOFCs) both in the absence and presence of CO2. It is found that the BSCF cathodes in the whole range of strontium doping levels show promising performance at 500–600 °C in the absence of CO2, among which the SrCo0.8Fe0.2O3−δ (SCF) cathode gives the highest power density while BaCo0.8Fe0.2O3−δ (BCF) cathode shows the lowest performance. The impedance analysis reveals that both the ohmic resistance and polarization resistance of the fuel cell increases when the strontium content decreases. It is believed that the microstructure and electrical conductivity simultaneously affect the process of oxygen reduction. The presence of CO2 deteriorates the BSCF performance by adsorbing on the cathode surface and thus obstructing the oxygen surface exchange reaction. The CO2 exerts a more intense influence on BSCF with higher barium content.

Low-temperature solid oxide fuel cells with a La0.8Sr0.2MnO3 (LSM) interlayer between the Ce0.9Gd0.1O1.95 (GDC) electrolyte membrane (20 μm) and the Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF)–GDC composite cathode are fabricated by sintering the BSCF–GDC composite cathodes at 900, 950 and 1000 °C. The results of scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) for a model LSM/BSCF bi-layer pellet suggest that Ba, Co and Fe in BSCF as well as La and Mn in LSM have diffused into their counter sides. The X-ray diffraction (XRD) results on the simulated cells also indicate the incorporation of La into the GDC electrolyte membrane and the mutual diffusion of elements between the LSM layer and the BSCF layer. Analysis of the impedance spectra and interfacial reaction activation energies shows that LSM interlayer accelerates the oxygen reduction. Considering a good cell performance and the highest open-circuit voltages (OCVs) at 600–500 °C, the optimum sintering temperature of BSCF–GDC composite cathode onto LSM interlayer is 900 °C.

Scandium-doped lanthanum strontium manganate La0.8Sr0.2Mn1−xScxO3−δ (LSMS) combined with YSZ as composite cathode for anode-supported solid oxide fuel cell is investigated. The LSMS powders are prepared using the modified Pechini method. The XRD and H2-TPR results reveal that non-stoichiometric defects are introduced into the perovskite lattice of LSMS samples as a result of Sc substitution, which leads to increased oxygen ion mobility in the Sc containing samples. But high level doping of Sc may results in the segregation of the Sc2O3 secondary phase at elevated temperature. The cells with the LSMS-containing cathodes exhibit higher performances, especially at lower temperatures, which can be ascribed to the increased oxygen anionic vacancies in the LSMS.

To bridge the sintering temperature gap between the electrolyte and the cathode, low-temperature anode supported solid oxide fuel cells (SOFCs) with various thickness of electrolyte interlayer were fabricated and investigated. The porous thin interlayer was dip-coated and fired onto the dense Ce0.9Gd0.1O1.95 (GDC) electrolyte surface. With humidified hydrogen as the fuel and air as the oxidant, the single cell with a 0.15 μm interlayer achieved the maximum power density (MPD) of 0.9 W cm−2 at 600 °C. The higher open circuit voltages (OCVs) (>0.9 V at 600 °C) were obtained in this study. The impedance results showed that the porous interlayer not only improved the interfacial contact between electrolyte and cathode, but also increased electrochemically active surface area. The cathode/electrolyte polarization resistance exhibited minimum when a 0.15 μm interlayer was added. The apparent activation energies derived from the Arrhenius plots of interfacial polarization resistances were about the same when the added interlayer was thinner, which indicated that the reaction mechanism did not change. However, the corresponding values were higher as the thick interlayer was introduced, which could be ascribed to the retarded oxygen ion transfer in the added porous layer. The cell area specific resistance (ASR) obtained by linear fitting I–V plot in the region of 0.6–0.7 V was higher than the ohmic resistance tested at OCV condition, and it was potentially attributed to the increased oxygen partial pressure at the anode as well as the contribution from polarization resistance, i.e. polarization of mass transport.

The composite cathodes of La0.4Ce0.6O1.8 (LDC)–La0.8Sr0.2MnO3 (LSM)–8 mol% yttria-stabilized zirconia (YSZ) with different LDC contents were investigated for anode-supported solid oxide fuel cells with thin film YSZ electrolyte. The oxygen temperature-programmed desorption profiles of the LDC–LSM–YSZ composites indicate that the addition of LDC increases surface oxygen vacancies. The cell performance was improved largely after the addition of LDC, and the best cell performance was achieved on the cells with the composite cathodes containing 10 wt% or 15 wt% LDC. The electrode polarization resistance was reduced significantly after the addition of LDC. At 800 °C and 650 °C, the polarization resistances of the cell with a 10 wt% LDC composite cathode are 70% and 40% of those of the cell with a LSM–YSZ composite cathode, respectively. The impedance spectra show that the processes associated with the dissociative adsorption of oxygen and diffusion of oxygen intermediates and/or oxygen ions on LSM surface and transfer of oxygen species at triple phase boundaries are accelerated after the addition of LDC.

A bi-layered composite cathode of La0.8Sr0.2MnO3 (LSM)-YSZ and LSM-La0.4Ce0.6O1.8 (LDC) was fabricated for anode-supported solid oxide fuel cells with a thin YSZ electrolyte film. The cell with the bi-layered composite cathode displayed better performance than the cell with the corresponding single-layered composite cathode of LSM-LDC or LSM-YSZ. At 650 °C, the cell with the bi-layered composite cathode gave a higher maximum power density than the cells with the single-layered LSM-LDC and LSM-YSZ composite cathodes, by 52% and 175%, respectively. The impedance spectra results show that the thin LSM-YSZ interlayer not only improves the cathode/electrolyte interface but also reduces the polarization resistance of the cathode. The activation energy for oxygen reduction on the bi-layered composite cathode is much smaller than that on LSM-YSZ composite cathode, and it is suggested that the special redox property of Ce4+/Ce3+ in LDC facilitates the oxygen reduction process on the bi-layered composite cathode. The cell with the bi-layered composite cathode operated quite stably during a 100 h run.

Lanthanum doped nickel and YSZ composite anode (LaNi–YSZ) exhibited a greatly reduced polarization resistance and high performance for electrochemical oxidation of hydrogen and methane, which resulted from a fine anode structure with a high dispersion of nickel catalyst and a high catalytic activity towards methane.

The reoxidation and reduction of a Ni–YSZ anode were investigated by monitoring the variation of ohmic resistance and the open circuit voltage of anode supported cells using electrochemical impedance spectroscopy. The ohmic resistance curves showed that anode reoxidation could be largely divided into three stages: an initial stage with a slow increase of ohmic resistance, a quick oxidation stage with a sharp increase in ohmic resistance and a final stage with a slight decrease of ohmic resistance. Reoxidation at 800 °C was a rapid process with a short initial stage, whereas reoxidation at 500 °C did not proceed in the last two stages. The OCV curves showed that reoxidation above 600 °C caused cracking of the YSZ electrolyte film.

Anode-supported solid oxide fuel cells (SOFCs) with lanthanum-doped ceria (LDC)/Sr-, Mg-doped LaGaO3 (LSGM) bilayered or LDC/LSGM/LDC trilayered electrolyte films were fabricated with a pure La0.6Sr0.4CoO3 (LSC) cathode. The behaviors of the two electrolytes in cells were investigated by using scanning electron microscopy, impedance spectroscopy and cell performance measurements. The reactions between LSGM and anode material can be suppressed by applying a ca. 15 μm LDC film. Due to the Co diffusion from the LSC cathode to the LSGM electrolyte during high temperature sintering, the electronic conductivity of the LDC electrolyte cannot be completely blocked with an LSGM layer below 50 μm, which leads to open-circuit potentials of these cells of ca. 0.988 V at 800 °C. The electrical conductivities of LDC and LSGM electrolytes in the cells under operation conditions are obtained from the dependence of the cell ohmic resistance on the electrolyte thickness. The electrical conductivity of LDC electrolyte is ca. 0.117 S cm−1 at 800 °C on the bilayered electrolyte cells with a 50 μm LSGM layer. The bilayer electrolyte cells with a 25 μm LDC layer at 800 °C, had a cell ohmic resistance two-stage linear dependence on the LSGM layer thickness, which showed the electrical conductivity of ca. 1.9 S cm−1 for the LSGM layer below 50 μm and 0.22 S cm−1 for the LSGM layer above 100 μm. With a LDC/LSGM/LDC trilayered electrolyte film for the anode-supported cell, an open-circuit potential of 1.043 V was achieved.

La0.8Sr0.2Mn1.1O3 (LSM1.1)–10 mol% Sc2O3-stabilized ZrO2 co-doped with CeO2 (ScSZ) composite cathodes were investigated for anode-supported solid oxide fuel cells (SOFCs) with thin 8 mol% Y2O3-stabilized ZrO2 (YSZ) electrolyte. X-ray diffraction (XRD) results indicated that the ScSZ electrolytes displayed good chemical compatibility with the nonstoichiometric LSM1.1 against co-firing at 1300 °C. Increasing the CeO2 content in the ScSZ electrolytes dramatically suppressed the electrode polarization resistance, which may be related to the improved surface oxygen exchange or the enlarged active area of cathode. The 5Ce10ScZr was the best electrolyte for the composite cathodes, which caused a small ohmic resistance decrease and the reduced polarization resistance and brought about the highest cell performance. The cell performances at lower temperatures seemed to rely on the electrode polarization resistance more seriously than the ohmic resistance. Compared with the cell impedance at higher temperatures, the higher the 5Ce10ScZr proportion in the composite cathodes, the smaller the increment of the charge transfer resistance at lower temperatures. The anode-supported SOFC with the LSM1.1–5Ce10ScZr (60 : 40) composite cathode achieved the maximum power densities of 0.82 W/cm2 at 650 °C and 2.24 W/cm2 at 800 °C, respectively.

Effect of redox cycling on a Ni–YSZ anode prepared from 50 wt.% NiO and 50 wt.% YSZ was investigated by using temperature-programmed reduction (TPR), XRD and SEM techniques. XRD results showed that NiO was formed during re-oxidation. Both the XRD and TPR results depicted that the conversion of nickel to NiO depended on the re-oxidation temperature. The oxidation of Ni to NiO occurred quickly in the initial several minutes and then reached a quasi equilibrium. The TPR profiles tracing the redox cycling showed that it brought continuous changes in the NiO micro-structure at 800 °C, whereas at 600 °C it had only little effects on the reduction of NiO. Re-oxidation resulted in the formation of spongy aggregates of NiO crystallites. Redox cycling at 800 °C led to a continuous decrease in the primary crystallite size of NiO and a high dispersion of the Ni particles. A continuous expansion of the slice sample was observed in both of the oxidized and reduced states during the redox cycling at 800 °C, whereas this process did not occur during the redox cycling at 600 °C.

The electrochemical properties of porous composite cathodes of La0.6Sr0.4CoO3 (LSC) and La0.45Ce0.55O2 (LDC) in anode supported lanthanum-doped ceria (LDC)/lanthanum gallate (LSGM) bilayer electrolyte single cells have been investigated. The composite cathodes with different LDC and LSC contents were in contact with the LSGM layer in the single cells. Comparing with the pure LSC cathode, the interfacial resistance decreased upon the addition of LDC and the optimum content of LDC was 50 wt.%. The variation in ohmic resistance suggests that the composite cathode can suppress Co diffusion from the cathode into the LSGM electrolyte during the firing of the composite cathode onto the electrolyte. The composite cathode with 50 wt.% LDC showed an ohmic resistance near to the calculated resistance of an electrolyte film. For the pure LSC cathode, the optimum firing temperature was about 1150 °C, at which both the electrolyte resistance and interface resistance were the smallest. The cathodic interfacial resistance was effectively reduced for the composite cathodes, especially for the cathode with 50 wt.% LDC, which might be due to the suppressing of sintering and the growth of LSC particles from LDC particles during the firing onto the electrolyte. The complicated effects of the composite cathode on the interfacial resistance and ohmic resistance resulted in the best single cell performance at 650 °C with a 50 wt.% LDC composite cathode, and the best cell performance above 700 °C on the single cell with pure LSC cathode.

•LSM–YSZ nanocomposite layer is infiltrated on LSM–YSZ, Al2O3 and YSZ scaffolds.•LSM–YSZ nanocomposite layer alone shows good ORR activity.•YSZ scaffold is best for raising ORR activity.(La0.8Sr0.2)0.9MnO3−δ-Y0.15Zr0.85O1.93 (LSM–YSZ) nanocomposite layer is infiltrated into three different scaffolds of ion-conductive YSZ, ionic and electronic conductive LSM–YSZ composite and insulating Al2O3 and used as cathode for anode supported cells. The cell performance and impedance spectra analysis reveal that the LSM–YSZ nanocomposite layer shows considerable high ORR activity using its own electronic and ionic conducting network, however, the electrochemical performance seems to be constrained by its limited ionic and electronic conductivity. The construction of ionic conducting path using YSZ scaffold is more effective for raising electrochemical performance than the construction of both electronic and ionic conducting paths using LSM–YSZ composite scaffold.

Doped ceria is commonly used to promote the performance of solid oxide fuel cells (SOFCs) with a lanthanum strontium manganite (LSM) cathode, but the oxygen reduction reaction (ORR) activity on the interface between LSM and doped ceria is not conclusive due to the complexity of the cathode and problematic analysis of the impedance spectra. Here, to elucidate the role of the LSM|GDC interface in the ORR, we constructed a simple LSM|GDC interface and analyzed the impedance data using a method based on the calculation of the distribution function of relaxation times (DRT). DRT analysis demonstrates that the ORR on the LSM|GDC interface possesses similar activation energies for oxygen dissociation and the subsequent oxygen atom reduction but involves an easier oxygen incorporation process in comparison with the LSM|YSZ interface. Addition of the GDC interlayer causes a decrease in cell performance because poor LSM|GDC interfaces lead to depressed dominant electrode processes of oxygen dissociation and the subsequent oxygen atom reduction. These results provide useful insight into the ORR on the LSM|GDC interface, favoring the design of a high-performance doped ceria-enhanced LSM cathode.

The YSZ electrolyte fuel cell with a ternary cathode composed of LSM–YSZ–Ce0.9Mn0.1O2−δ exhibits ca. 2.6 times higher current density than that with a binary cathode composed of LSM–YSZ at 600 °C.