Solid Oxide Fuel Cell Cathode Research Articles

Self-assembled cubic-hexagonal perovskite nanocomposite as intermediate-temperature solid oxide fuel cell cathode

Self-assembly is an emerging strategy for preparing composite cathodes with good oxygen electrochemical reduction activity and congenital chemical compatibility for intermediate-temperature solid oxide fuel cell (IT-SOFC). Here we report that a self-assembled BaCo0.6Zr0.4O3-δ (BZC-BC) nanocomposite is prepared through one-pot glycine-nitrate process and exhibits high cathode performance. The BZC-BC nanocomposite is composed of 62 mol% cubic perovskite BaZr0.82Co0.18O3-δ (BZC) as an ionic conductor and 38 mol% hexagonal perovskite BaCo0.96Zr0.04O2.6+δ (12H-BC) as a mixed ionic and electronic conductor. The BZC-BC nanocomposite has the pomegranate-like particles aggregated with a larger number of nanoparticles (50-100 nm) which greatly enlarge the three-phase boundary sites. The BZC-BC nanocomposite exhibits a thermal expansion coefficient of 12.89 × 10−6 K−1 well-matched with that of Ce0.8Gd0.2O3-δ (12.84 × 10−6 K−1) electrolyte. The high electro-catalytic activity of BZC-BC nanocomposite cathode for oxygen reduction is reflected by the low polarization resistances of oxygen ions incorporation at cathode/electrolyte interface (0.02823 Ω cm2), oxygen species diffusion (0.03702 Ω cm2) and oxygen adsorptive dissociation (0.07609 Ω cm2) at 700 °C. The single cell with BZC-BC nanocomposite cathode achieves the maximum power density of 1094 mW cm−2 at 650 °C and shows good stability under 25 h run.

Perovskite Conversion Coatings as Novel and Simple Approach for Improving Functional Performance of Ferritic Stainless Steel SOFC Interconnects

AbstractA novel type of iron conversion process has been recently developed to produce dense and adherent LaFeO3 perovskite coatings onto ferritic stainless steel surfaces by reaction with La2O3 dissolved in specially‐formulated alkali molten carbonate baths. The major application of LaFeO3 perovskite coatings is for use as electrically conductive and Cr barrier layers for enhancing the functional performance of solid oxide fuel cell (SOFC) stainless steel interconnects. An overview of the molten salt bath conversion process including the effect of chemical accelerants on structure and morphology of the deposited perovskite coatings is illustrated in this work. Latest results on SOFC coating functional properties obtained in recent European Union (EU) funded projects are also briefly mentioned. In particular, the tight correlation between coating thickness and electrical functional properties in terms of area specific resistance is highlighted here. Although thickness dependency may indicate a mediocre electrical conductivity of LaFeO3 coatings produced by the conversion process, nonetheless very promising ASR results could be obtained in SOFC cathode environments at 700 °C with optimized coating structures and appropriate low coating thickness, thus suggesting a high potential of the conversion process for SOFC interconnect applications.

LaxPr4−xNi3O10−δ: Mixed A-Site Cation Higher-Order Ruddlesden-Popper Phase Materials as Intermediate-Temperature Solid Oxide Fuel Cell Cathodes

Systematic studies of the air electrode and full solid oxide fuel cell performance of La3PrNi3O9.76, and La2Pr2Ni3O9.65 n = 3 Ruddlesden–Popper phases are reported. These phases were found to adopt orthorhombic symmetry with a decrease in lattice parameters on increasing Pr content, consistent with the solid solution series end members. From electrochemical impedance spectroscopy measurements of symmetrical cells, the electrodes were found to possess area specific resistances of 0.07 Ω cm2 for the La2Pr2Ni3O9.65 cathode and 0.10 Ω cm2 for the La3PrNi3O9.76 cathode at 750 °C, representing a significant improvement on previously reported compositions. This significant improvement in performance is attributed to the optimisation of the electrode microstructure, introduction of an electrolyte interlayer and the resulting improved adhesion of the electrode layer. Following this development, the new electrode materials were tested for their single-cell performance, with the maximum power densities obtained for La2Pr2Ni3O9.65 and La3PrNi3O9.76 being 390 mW cm−2 and 400 mW cm−2 at 800 °C, respectively. As these single-cell measurements were based on thick electrolytes, there is considerable scope to enhance over cell performance in future developments.

A discrete element model simulation of structure and bonding at interfaces between cathode and cathode contact paste in solid oxide fuel cells

For the first time, the impacts of solid oxide fuel cell (SOFC) cathode/contact paste interface roughness on mechanical strength are quantified using a particle based numerical technique in micro-scale. This work identifies a potential new direction to develop high strength SOFC stack structures to enhance SOFC long-term durability with most commonly used material. To model the effect of different interface roughness values on the integrity of the dissimilar material joint as well as the fracture behavior of the bonded interface, a discrete element model (DEM) method is adapted due to many unique advantages. The model demonstrates that interfacial toughness increases with interfacial roughness and sintering temperatures. In particular, the roughened interface can increase ultimate mechanical strength to a factor of 2–3 compared with the smooth interface. Moreover, contact paste with higher stiffness properties can be beneficial in terms of delaying the onset of the initial interfacial damage at rough interfaces. The results also show that toughness decreases with increasing strength ratio between the interface and contact paste. It is expected that this study can provide guidance to improve SOFC cathode design with better mechanical strengths, which would benefit the mechanical integrity of the SOFC stack.

Strain-induced structure and oxygen transport interactions in epitaxial La0.6Sr0.4CoO3\u2212\u03b4 thin films

The possibility to control oxygen transport in one of the most promising solid oxide fuel cell cathode materials, La0.6Sr0.4CoO3−δ, by controlling lattice strain raises questions regarding the contribution of atomic scale effects. Here, high-resolution transmission electron microscopy revealed the different atomic structures in La0.6Sr0.4CoO3−δ thin films grown under tensile and compressive strain conditions. The atomic structure of the tensile-strained film indicated significant local concentration of the oxygen vacancies, with the average value of the oxygen non-stoichiometry being much larger than for the compressive-strained film. In addition to the vacancy concentration differences that are measured by isotope exchange depth profiling, significant vacancy ordering was found in tensile-strained films. This understanding might be useful for tuning the atomic structure of La0.6Sr0.4CoO3−δ thin films to optimize cathode performance.

Development of solid oxide fuel cells using high-frequency plasma spraying technologies

The paper describes the topical issues and the latest achievements in the development of materials with high electrochemical characteristics for single cells and small assemblies of solid oxide fuel cells (SOFC). The authors propose planar SOFC technology which includes sequential deposition of all layers of a thin-film cell on a porous metallic substrate by plasma techniques. The method allows developing porous SOFC anode and cathode, which increases the active area of electrochemical reaction, reduces the spread of technological parameters (in particular, the spread in thickness and porosity of a solid electrolyte), improves SOFC performance and reduces the mass and size of SOFC assemblies. The paper also describes the physics of plasma spraying process in individual cells and SOFC structures. The proposed method is an alternative to traditional SOFC production methods; it eliminates the necessity to use agglomeration technology or other heat treatment. Moreover, it opens up the prospects for automated continuous production process. The appropriate SOFC production equipment is developed, for stationary and mobile use. Further studies will be focused on the task of reducing the weight of SOFC assemblies, which allows using them as an auxiliary power unit for on-board power supply, for example, for cars, airplanes and spaceships.

BaCe0.7–xZr0.2Y0.1FexO3–δ derived from proton-conducting electrolytes: A way of designing chemically compatible cathodes for solid oxide fuel cells

The present study describes the rational engineering, preparation and characterisation of new mixed ionic-electronic conductors (MIECs) having great potential for application in solid oxide fuel cells (SOFCs) based on proton-conducting electrolytes. The developed MIECs are derived from promising Ba(Ce,Zr)O 3 -materials doped with iron as a transition element: BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ (x = 0–0.7, Δx = 0.1). The comprehensive analysis of the functional properties (crystal structure, densification, microstructure, defect structure, thermal expansion behaviour, electrical conductivity) indicate that a moderate iron content is beneficial in order to achieve a certain compromise. In detail, the gradual Fe-doping results in an enhancement of transport properties (including, ionic-electronic conductivity level) and deterioration of mechanical characteristics (an increase of average thermal expansion coefficient values). The composition with x = 0.6, identified as more optimal, was used as a cathode for an intermediate-temperature SOFC; this cathode displays a satisfactory polarisation resistance level, 0.21 Ω cm 2 at 700 °C, without the use of any additional electroactivation technique. The obtained results indicate that BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ MIECs having one of the highest chemical compatibility with state-of-the-art proton-conducting electrolytes can be considered as advanced electrodes for designing new solid oxide electrochemical devices with prolonged and stable operation mode. • BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ (BCZYFx) materials were prepared for the first time. • The BCZYFx materials are single-phase across the entire x range (0 = x ≤ 0.7). • Fe-doping leads to an increase in both ionic and electronic conductivities (at x ≥ 0.4). • At the same time, TECs values increase and chemical strain becomes more pronounced. • BCZYF0.6 with an optimal combination of properties was utilised as a SOFC cathode.

Enhanced Cr-tolerance of an SOFC cathode by an efficient electro-catalyst coating

Abstract The durability and electro-catalytic activity for oxygen reduction reaction (ORR) of solid oxide fuel cells (SOFCs) cathode often suffer from severe degradation due to poisoning effects such as Cr from interconnectors. Here we report our findings in the development of a Cr-tolerant catalyst, BaCoO3-x (BCO) nano-particles, which can dramatically enhance the ORR activity and durability of a state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) cathode exposed to Crofer 22APU. For example, the polarization resistance (Rp) of a bare LSCF cathode increases from ~0.4 to ~1.5 Ωcm2 after 100 hs exposure to Cr in air with 3% H2O at 750 °C. In contrast, Rp of a BCO-coated LSCF cathode remains to be ~0.05 Ωcm2 under the same condition, suggesting that BCO is catalytically active to ORR but inert to Cr-poisoning. At 700 °C, the single cells with the BCO-coated LSCF cathode show an excellent peak power density of ~0.514 Wcm−2 and significantly enhanced durability (degradation rate of 0.086 %h−1 at 0.8 V), much better than those of cells with a bare LSCF cathode (~0.448 Wcm−2 and degradation rate of 0.31 %h−1 at 0.8 V). Raman analysis indicated that the presence of the BCO catalyst coating greatly reduced the amount of Cr accumulated on the cathode surface, thus alleviating the formation of SrCrO4.

The tortuosity factor effect on solid oxide fuel cell performance

In this work, the three-dimensional (3-D) microstructure of Solid Oxide Fuel Cell (SOFC) composite electrode is reconstructed by a random particle packing procedure and a geometrical dilating process, based on which the different tortuosity factors (τ) are calculated by solving the steady state charge conservation equation in different percolated networks. After that, the effects of the different τ on cell performance are analyzed by a one-dimensional (1-D) SOFC performance simulation model, in which the electrochemical reactions and the gas/ion/electron transport are coupled. The results indicate that the tortuosity factor of the ion-conducting phase in SOFC cathode (τio,c) plays the most important role and up to 62% SOFC performance improvement can be expected by decreasing τio,c. In addition, by decreasing the tortuosity factor of the gas phase (τgas,a) and the ion-conducting phase in SOFC anode (τio,a), 1.7% and 17% performance improvement can be achieved, respectively. This work could help improving SOFC performance by modifying the tortuous transport paths in SOFC porous electrodes.

A novel Nb and Cu co-doped SrCoO3-δ cathode for intermediate temperature solid oxide fuel cells

The extensive explorations of potential cathode materials are prominently critical for the rapid development of high performance solid oxide fuel cells (SOFCs). Herein, we develop a novel Nb and Cu co-doped SrCoO3-δ (SCNC) cathode base on solid state reaction, which exhibits decent compatibility with gadolinium doped cerium oxide (GDC) electrolyte. The SCNC is successfully stabilized with cubic structure at room temperature when incorporating of small amount of high valence Nb5+. Meanwhile, the oxygen vacancy concentration of SCNC is efficiently improved with the addition of Cu. The Nb and Cu co-doping also substantially promotes the electronic conductivity, achieving 550 S cm−1 for the optical doped SrCo0.85Nb0.05Cu0.10O3-δ (SCNC10) at 400 °C. In addition, the polarization of SCNC is remarkably reduced, reaching as low as 0.021 Ω cm2 for SCNC10 at 700 °C. The activation energy for reaction is also significantly lowered to 0.78 eV. The reaction order m is deduced to be about 0.30, implying that the rate determination step for SCNC10 is the charge transfer reaction. The peak power density of the single cell reaches 780 mW cm−2 at 800 °C. All these outstanding performances demonstrate that SCNC is a promising cathode for SOFCs when operating at intermediate temperature (IT).

A Zn-Doped Ba0.5Sr0.5Co0.8Fe0.2O3-δ Perovskite Cathode with Enhanced ORR Catalytic Activity for SOFCs

The insufficient oxygen reduction reaction activity of cathode materials is one of the main obstacles to decreasing the operating temperature of solid oxide fuel cells (SOFCs). Here, we report a Zn-doped perovskite oxide Ba0.5Sr0.5(Co0.8Fe0.2)0.96Zn0.04O3-δ (BSCFZ) as the SOFC cathode, which exhibits much higher electrocatalytical activity than Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) for the oxygen reduction reaction (ORR). The BSCFZ cathode exhibited a polarization resistance of only 0.23 and 0.03 Ω·cm2 on a symmetrical cell at 600 and 750 °C, respectively. The corresponding maximum power density of 0.58 W·cm−2 was obtained in the yittria-stabilized zirconia (YSZ)-based anode-supported single cell at 750 °C, an increase by 35% in comparison to the BSCF cathode. The enhanced performance can be attributed to a better balance of oxygen vacancies, surface electron transfer and ionic mobility as promoted by the low valence Zn2+ doping. This work proves that Zn-doping is a highly effective strategy to further enhance the ORR electrocatalytic activity of state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode material for intermediate temperature SOFCs.

Investigation of structural, electrical and electrochemical properties of La0.6Sr0.4Fe0.8Mn0.2O3-δ as an intermediate temperature solid oxide fuel cell cathode

La0.6Sr0.4Fe0.8Mn0.2O3 (LSFM) compound is synthesized by sol-gel method and evaluated as a cathode material for the intermediate temperature solid oxide fuel cell (IT-SOFC). X-ray diffraction (XRD) indicates that the LSFM has a rhombohedral structure with R-3c space group symmetry. The XRD patterns reveal very small amount of impurity phase in the LSFM and Y2O3-stabilized ZrO2 (YSZ) mixture powders sintered at 600, 700, 800 and 850 °C for a week. The maximum electrical conductivity of LSFM is about 35.35 S cm−1 at 783 °C in the air. The oxygen chemical diffusion coefficients, DChem, are increased from 1.39 × 10−6 up to 1.44 × 10−5 cm2 s−1. Besides, the oxygen surface exchange coefficients, kChem, are obtained to lie between 2.9 × 10−3 and 1.86 × 10−2 cm s−1 in a temperature range of 600–800 °C. The area-specific resistances (ASRs) of the LSFM symmetrical cell are 7.53, 1.53, 1.13, 0.46 and 0.31 Ω cm2 at 600, 650, 700, 750 and 800 °C respectively, and related activation energy, Ea, is about 1.23 eV.

Stable, efficient and cost-competitive Ni-substituted Sr(Ti,Fe)O3 cathode for solid oxide fuel cell: Effect of A-site deficiency

In this work, a cost-competitive oxide system of Ni-substituted Sr1-xTi0.3Fe0.6Ni0.1O3-δ (STFN, x = 0, 0.02, 0.05), is evaluated as Solid Oxide Fuel Cell cathode. All STFN oxides present cubic perovskite structure with maximum conductivities over 22 S/cm in air. The introduction of Sr deficiency yields higher oxygen vacancy and lower thermal expansion coefficient. As a result, the cathode polarization resistance of 0.107 Ω cm2 is obtained for Sr0.95Ti0.3Fe0.6Ni0.1O3-δ (STFN-95) at 750 °C and pO2=0.21atm, with weak oxygen partial pressure dependence. Specially, STFN-95 presents higher stability with slower Rp increasing rate in lower oxygen partial pressure of 0.14 atm than in 0.21 atm, which greatly facilitates the cathode practical application in SOFC stack under high air utilization condition. Finally, a stable operation of 400 h is achieved using STFN-95 cathode on anode supported single cell at 750 °C, without showing Sr and other elements diffusions.

Enhancing the oxygen reduction activity of PrBaCo2O5+δ double perovskite cathode by tailoring the calcination temperatures

In this study, the oxygen reduction activity of PrBaCo2O5+δ (PBC) double perovskite is remarkably enhanced by rationally tuning the calcination temperatures of the cathode precursor for solid oxide fuel cells (SOFCs). Effects of the calcination temperatures on the phase structure, microstructure, surface area and oxygen reduction reaction (ORR) activity of PBC cathode is systematically investigated. The cathode with optimized calcination temperature (900 °C, PBC-900) shows excellent activity and stability for ORR at 600 °C in terms of area specific resistances (ASRs). A distinctive low ASR of 0.068 Ω cm2 is obtained at 600 °C for PBC-900, which is 92.6%, 34.6% and 15.0% lower than PBC-800, PBC-1000 and PBC-1100, respectively. After operating for 250 h in air at 600 °C, the ASR value of PBC-900 is not significantly reduced. Furthermore, a single cell with PBC-900 cathode delivers attractive peak power density of 1.60 W cm−2 at 600 °C. The present study suggests that the ORR activity of PBC cathode can be greatly boosted by rationally tailoring the calcination temperatures, which may bring new avenue for the design of highly active cathodes for SOFCs.

High-performance solid oxide fuel cells with fiber-based cathodes for low-temperature operation

Low-temperature operation of solid oxide fuel cells (SOFCs) results in deterioration in electrochemical performance due to sluggish oxygen reduction reaction (ORR) at the cathode. To enhance the reaction pathway for ORR, La0.8Sr0.2MnO3 (LSM) nanofibers were fabricated by electrospinning and used for low-temperature solid oxide fuel cells operated at 600–700 °C. The morphological and structural characteristics show that the electrospun LSM nanofiber has a highly crystallized perovskite structure with a uniform elemental distribution. The average diameter of the LSM nanofiber after sintering is 380 nm. A symmetric cell of nanofiber-based LSM cathode on scandia-stabilized zirconia (SSZ) electrolyte pellet exhibits much lower area specific resistances compared to commercial LSM powder-based cathode. A single cell based on the nanofiber LSM cathode on yttrium-doped barium cerate-zirconia (BCZY) electrolyte exhibits a power density of 0.35 Wcm−2 at 600 °C, which increases to 0.85 Wcm−2 at 700 °C. The cell has an area specific resistance (ASR) of 0.46 Ωcm2 at 600 °C, which decreases to 0.07 Ωcm2 at 700 °C. The results indicate that the LSM electrode fabricated by the electrospinning process produces a nanostructured porous electrode which optimizes the microstructure and significantly enhances the ORR at the cathode of SOFCs.

A Cobalt-Free Multi-Phase Nanocomposite as Near-Ideal Cathode of Intermediate-Temperature Solid Oxide Fuel Cells Developed by Smart Self-Assembly.

An ideal solid oxide fuel cell (SOFC) cathode should meet multiple requirements, i.e., high activity for oxygen reduction reaction (ORR), good conductivity, favorable stability, and sound thermo-mechanical/chemical compatibility with electrolyte, while it is very challenging to achieve all these requirements based on a single-phase material. Herein, a cost-effective multi-phase nanocomposite, facilely synthesized through smart self-assembly at high temperature, is developed as a near-ideal cathode of intermediate-temperature SOFCs, showing high ORR activity (an area-specific resistance of ≈0.028 Ω cm2 and a power output of 1208 mW cm-2 at 650 °C), affordable conductivity (21.5 S cm-1 at 650 °C), favorable stability (560 h operation in single cell), excellent chemical compatibility with Sm0.2 Ce0.8 O1.9 electrolyte, and reduced thermal expansion coefficient (≈16.8 × 10-6 K-1 ). Such a nanocomposite (Sr0.9 Ce0.1 Fe0.8 Ni0.2 O3- δ ) is composed of a single perovskite main phase (77.2 wt%), a Ruddlesden-Popper (RP) second phase (13.3 wt%), and surface-decorated NiO (5.8 wt%) and CeO2 (3.7 wt%) minor phases. The RP phase promotes the oxygen bulk diffusion while NiO and CeO2 nanoparticles facilitate the oxygen surface process and O2- migration from the surface to the main phase, respectively. The strong interaction between four phases in nanodomain creates a synergistic effect, leading to the superior ORR activity.

Hybrid Electrochemical Deposition Route for the Facile Nanofabrication of a Cr-Poisoning-Tolerant La(Ni,Fe)O3-δ Cathode for Solid Oxide Fuel Cells.

Cr poisoning of cathode materials is one of the main degradation issues hampering the operation of solid oxide fuel cells (SOFCs). To overcome this shortcoming, LaNi0.6Fe0.4O3-δ (LNF) has been developed as an alternative cathode material owing to its superior chemical stability in Cr environments. In this study, we develop a hybrid electrochemical deposition technique to fabricate a nanostructured LNF-gadolinium-doped ceria (GDC) (n-LNF-GDC) cathode with enhanced active reaction sites for the oxygen reduction reaction. For this purpose, Fe and Ni cations are co-deposited onto an electrically conductive carbon nanotube-modified GDC backbone by electroplating, whereas La cations are successively deposited through a chemically assisted electrodeposition method. The proposed method involves a low-temperature (900 °C) calcination step of electrodeposited cations, which avoids the need of fabricating a GDC diffusion barrier layer which is otherwise needed to avoid the formation of insulating phases (e.g., La2Zr2O7) when fabricating by conventional high-temperature (≥1000 °C) sintering. Scanning electron microscopy images reveal a unique nanofibrous structure of n-LNF-GDC, which is believed to play an instrumental role in enhancing the electrochemical characteristics by increasing the active triple-phase boundaries. An anode-supported SOFC with the n-LNF-GDC cathode showed the superior performance of 0.984 W cm-2 at an intermediate temperature of 750 °C as compared to the power densities of 0.495 and 0.874 W cm-2 produced by LNF-GDC and state-of-the-art La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-GDC composite cathodes fabricated by conventional sintering. A short-term accelerated Cr-poisoning durability test indicated good electrochemical stability of n-LNF-GDC, whereas LSCF exhibited severe degradation. The electrochemically engineered nanostructured n-LNF-GDC can serve as an effective cathode for SOFCs to achieve high performance and long-term durability.

Constructing a pathway for mixed ion and electron transfer reactions for O2 incorporation in Pr0.1Ce0.9O2−x

In interfacial charge-transfer reactions, the complexity of the reaction pathway increases with the number of charges transferred, and becomes even greater when the reaction involves both electrons (charge) and ions (mass). These so-called mixed ion and electron transfer (MIET) reactions are crucial in intercalation/insertion electrochemistry, such as that occurring in oxygen reduction/evolution electrocatalysts and lithium-ion battery electrodes. Understanding MIET reaction pathways, particularly identifying the rate-determining step (RDS), is crucial for engineering interfaces at the molecular, electronic and point defect levels. Here we develop a generalizable experimental and analysis framework for constructing the reaction pathway for the incorporation of O2(g) in Pr0.1Ce0.9O2−x. We converge on four candidates for the RDS (dissociation of neutral oxygen adsorbate) out of more than 100 possibilities by measuring the current density–overpotential curves while controlling both oxygen activity in the solid and oxygen gas partial pressure, and by quantifying the chemical and electrostatic driving forces using operando ambient pressure X-ray photoelectron spectroscopy. Identifying rate-determining steps (RDSs) is one of the most challenging aspects of catalysis. This work presents a general framework to identify the RDS of mixed ion and electron transfer reactions, and applies it to the four-electron/two-ion O2 reduction in solid-oxide fuel cell cathodes, converging on four RDS out of more than 100 possible candidates.

Novel materials for solid oxide fuel cells cathodes and oxygen separation membranes: Fundamentals of oxygen transport and performance

In the field of modern hydrogen energy, obtaining pure hydrogen and syngas and then being able to use them for green energy production are significant problems. Developing solid oxide fuel cells (SOFC) and catalytic membranes for oxygen separation as well as materials for these devices is one of the most likely ways to solve these problems. In this work, the authors’ recent studies in this field are reviewed; the fundamentals of developing materials for SOFC cathodes and oxygen separation membranes’ permselective layers based on research of their oxygen mobility and surface reactivity are presented. Ruddlesden – Popper phases Ln2–xCaxNiO4+δ (LnCNO) and perovskite-fluorite nanocomposites PrNi0.5Co0.5O3–δ–Ce0.9Y0.1O2–δ (PNC–YDC) were studied by isotope exchange of oxygen with C18O2 and 18O2 in flow and closed reactors. For LnCNO a high oxygen mobility was shown (D* ~ 10–7 cm2/s at 700 °C), being provided by the cooperative mechanism of oxygen migration involving both regular and highly-mobile interstitial oxygen. For PNC–YDC dominated a wide fast diffusion channel via fluorite phase and interphases due to features of the redistribution of cations resulting in superior oxygen mobility (D* ~ 10–8 cm2/s at 700 °C). After optimization of composition and nanodomain structure of these materials, as cathodes of SOFC they provided a high power density, while for asymmetric supported oxygen separation membranes – a high oxygen permeability.

A hierarchical hybrid electrode for rapid oxygen reduction reaction below 800°C

The 3-D backbones with ionic conductivity are first built by sintering Ce0.8Sm0.2O1.9 silks, then Ca3Co2O6 nanoparticles as electrocatalyst are filled in by infiltrating ionic solution, as a result, a hybrid electrode with hierarchical structure is constructed as the cathode of solid oxide fuel cells. Compared with the single-phase Ca3Co2O6 bulk cathode and common Ca3Co2O6-Ce0.8Sm0.2O1.9 composite one, this hybrid electrode is very active for oxygen reduction reaction. At 800?C, area specific resistance with this cathode is reduced to 0.062 ?cm2, and power density peak with the electrolyte-supported single-cell is promoted to 760 mW/cm2. The superior catalytical activity is attributed to the enlarged area for surface oxygen exchange kinetics and enhanced ionic transport behaviour.