SmBa0.5Sr0.5Cu2O5+δ and SmBa0.5Sr0.5CuFeO5+δ layered perovskite oxides as cathodes for IT-SOFCs

Novel Cobalt-free layered perovskite oxides SmBa_0.5Sr_0.5Cu₂O_5+δ (SBSCO) and SmBa_0.5Sr_0.5CuFeO_5+δ (SBSCFO) were investigated as cathode materials for intermediate-temperature solid fuel cells (IT-SOFCs). The thermal expansion coefficients (TEC) of SBSCO and SBSCFO were 14.1 × 10⁻⁶/°C and 14.9 × 10⁻⁶/°C in 50 °C–800 °C, which were more compatible with electrolyte than cobalt-based cathodes. When A′-site is partially substituted by Sr, the conductivity of SBSCO and SBSCFO had been improved. The max electrical conductivity of SBSCO was 277.7 S cm⁻¹, about one order of magnitude higher than SmBaCu₂O_5+δ. Polarization resistance of SBSCO is 0.25 Ω cm² at 650 °C, which is twice lower than that of SmBaCu₂O_5+δ (SBCO). This implies SBSCO has higher activity for oxygen reduction than SBCO. Preliminary results indicate that SBSCO are promising as cathodes for IT-SOFCs.     

Electrochemical performance of PrBaCo2O5+δ layered perovskite as an intermediate-temperature solid oxide fuel cell cathode

PrBaCo₂O_5+δ (PBCO) powder was prepared by a combined EDTA and citrate complexing method. The electrochemical performance of PBCO as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs) was evaluated. A porous layer of PBCO was deposited on a 42 μm thick electrolyte consisting of Ce_0.8Sm_0.2O_1.9 (SDC), prepared by a dry-pressing process. A fuel cell with a structure PBCO/SDC/Ni-SDC provides a maximum power density of 866, 583, 313 and 115 mW cm⁻² at 650, 600, 550 and 500 °C, respectively, using hydrogen as the fuel and stationary air as the oxidant. The total resistance of the cell was about 0.41, 0.51, 0.57 and 0.77 Ω cm², respectively. This encouraging data identifies PBCO as a potential cathode material for IT-SOFCs.     

Synthesis, characterization and evaluation of PrBaCo2−xFexO5+δ as cathodes for intermediate-temperature solid oxide fuel cells

Iron doped layered structured perovskites, PrBaCo_2−xFe_xO_5+δ (x = 0, 0.5, 1.0, 1.5 and 2.0), are evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of dopant content are investigated on their structural and electrochemical properties including crystalline structure, oxygen nonstoichiometry, stability in presence of CO₂, compatibility with electrolytes, thermal expansion coefficient, electrical conductivity, and cathodic interfacial polarization resistance. The lattice parameter and oxygen nonstoichiometry content, δ, at room temperature increase, whereas the conductivity, thermal expansion coefficient, and cathodic performance decrease with increasing iron content, x. PrBaCo_2−xFe_xO_5+δ exhibit excellent stability at 700 °C in atmosphere consisting of 3% CO₂ and 97% air, show good chemical compatibility with doped ceria electrolytes at 1000 °C, but react readily with yttria-stabilized zirconia at 700 °C. Even with a Co-free PrBaFe₂O_5+δ as the electrode, a symmetrical cell demonstrates area specific resistance of 0.18 Ω cm² at 700 °C with samaria-doped ceria electrolyte. The resistance is lower than those for typical Co-free electrodes reported in the literatures, suggesting that PrBaCo_2−xFe_xO_5+δ are potential promising cathode materials for IT-SOFCs.     

Layered perovskite LnBa0.5Sr0.5Cu2O5+δ (Ln = Pr and Nd) as cobalt-free cathode materials for solid oxide fuel cells

Cobalt-free layered perovskite LnBa_0.5Sr_0.5Cu₂O_5+δ (Ln = Pr and Nd, PBSC and NBSC) powders are prepared using combined citrate and EDTA complexing method. The performance of PBSC and NBSC cathode materials are evaluated for solid oxide fuel cells (SOFCs). Two oxidation states (Cu²⁺/Cu⁺) for Cu ions exist in LnBa_0.5Sr_0.5Cu₂O_5+δ oxides. The main valence of Pr ions in PBSC is 3+. The average thermal expansion coefficients (TECs) of PBSC and NBSC are 14.2 and 14.6 × 10^?6 K^?1 between 30 and 950 °C, which are similar to the TECs of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3?δ (LSGM) intermediate-temperature electrolyte. The electrical conductivity of PBSC is slightly higher than that of NBSC. At 800 °C, the polarization resistance (R_p) values of the PBSC and NBSC cathodes on the LSGM electrolyte are 0.043 and 0.057 Ω cm², respectively. The electrolyte-supported single cells were prepared by using PBSC and NBSC as cathode, LSGM as electrolyte (300 μm thickness), Ce_0.9Sm_0.1O_1.95 (SDC) as interlayer and Ni/SDC as anode. At 850 °C, the maximal power densities are obtained as 681 and 651 mW cm^?2 for PBSC and NBSC cathodes.     

Effect of chromium poisoning on the electrochemical properties of NdBaCo2O5+δ cathode for IT-SOFCs

The effect of the Cr poisoning on the electrochemical properties of NdBaCo₂O_5+δ cathode for IT-SOFCs was investigated by the electrochemical impedance spectroscopy (EIS) and the cathodic polarization analysis. With the Cr poisoning, the area-specific resistances (ASRs) increased at 500–600 °C and did not increase with the increasing temperature. The Cr poisoning made a negative effect on the oxygen reduction reaction (ORR) below 600 °C. Besides, the Cr poisoning decreased the exchange current density i₀. The activation energies of i₀ were higher than those of the ASRs, indicating that the charge transfer process was the rate-determining step for the ORR. With or without the Cr poisoning, the polarization curves were independent of the on the sweep rate, indicating that there were no mass transport limitations on the ORR rate. Hence, the Cr poisoning deteriorated the charge transfer process of the ORR for NdBaCo₂O_5+δ and decreased the ORR activity.     

High-performance PrBaCo2O5+δ-Ce0.8Sm0.2O1.9 composite cathodes for intermediate temperature solid oxide fuel cell

PrBaCo₂O_5+δ-Ce_0.8Sm_0.2O_1.9 (PBCO-SDC) composite material are prepared and characterized as cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction result proves that there are no obvious reaction between the PBCO and SDC after calcination at 1100 °C for 3 h. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures shows that the addition of SDC to PBCO improved remarkably the electrochemical performance of a PBCO cathode, and that a PBCO-30SDC cathode exhibits the best electrochemical performance in the PBCO-xSDC system. The total interfacial resistances R_p is the smallest when the content of SDC is 30 wt%, where the value is 0.035 Ω cm² at 750 °C, 0.072 Ω cm² at 700 °C, and 0.148 Ω cm² at 650 °C, much lower than the corresponding interfacial resistance for pure PBCO. The maximum power density of an anode-supported single cell with PBCO-30SDC cathode, Ni-SDC anode, and dense thin SDC/LSGM (La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ)/SDC tri-layer electrolyte are 364, 521 and 741 mW cm⁻² at 700, 750 and 800 °C, respectively.     

Electrochemical performance of nanostructured La0.6Sr0.4CoO3−δ and Sm0.5Sr0.5CoO3−δ cathodes for IT-SOFCs

The electrochemical performance of nanostructured cathodes for IT-SOFCs based on perovskite-type mixed ionic/electronic conductors (MIECs) is investigated. Different compounds (La_0.6Sr_0.4CoO_3−δ and Sm_0.5Sr_0.5CoO_3−δ) and synthesis methods (freeze-drying and citrate complexation) were evaluated. These materials exhibited excellent performance (area-specific resistance values in the range of 0.05-0.20 Ω cm² for an operating temperature of 700 °C), which improved with decreasing grain size. This performance can be attributed to the high specific surface area of these nanostructured cathodes, thus dramatically increasing the number of active sites for the oxygen reduction reaction. Under these conditions, the electrochemical properties are mainly controlled by oxide ion diffusion through the MIEC cathode, which becomes faster with decreasing grain size.     

Characterization of cation-ordered perovskite oxide LaBaCo2O5+δ as cathode of intermediate-temperature solid oxide fuel cells

A-site cation-ordered perovskite oxide LaBaCo₂O_5+δ (LBCO) was synthesized and evaluated as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs). LBCO was structurally stable when calcined at 850 °C in air but transformed into cation-disordered structure at 1050 °C. LBCO showed chemical compatibility with Gd_0.1Ce_0.9O_1.95 (GDC) electrolyte at 850 °C and 1000 °C in air. Conductivity of LBCO firstly increased slightly with higher temperature to a maximum of 470 S cm⁻¹ at ∼250 °C and then decreased gradually with further increase in temperature. Electrochemical impedance spectra of the LBCO/GDC/LBCO symmetric cell were measured, and electrode reaction mechanism for the LBCO cathode was analyzed. The electrode polarization resistance of LBCO was mainly contributed by oxygen ionic transfer across the cathode/electrolyte interface and oxygen atom diffusion-electronic charge transfer process. Low area-specific resistances with values ranging from 0.15 Ω cm² at 650 °C to 0.0086 Ω cm² at 800 °C were obtained. These results have demonstrated that the A-site cation-ordered perovskite oxide LBCO is a promising cathode material for IT-SOFCs.     

Layered perovskite PrBa0.5Sr0.5Co2O5+δ as high performance cathode for solid oxide fuel cells using oxide proton-conducting electrolyte

The layered perovskite PrBa_0.5Sr_0.5Co₂O_5+δ (PBSC) was investigated as a cathode material for a solid oxide fuel cell using an oxide proton conductor based on BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY). The sintering conditions for the PBSC-BZCY composite cathode were optimized, resulting in the lowest area-specific resistance and apparent activation energy obtained with the cathode sintered at 1200 °C for 2 h. The maximum power densities of the PBSC-BZCY/BZCY/NiO-BZCY cell were 0.179, 0.274, 0.395, and 0.522 W cm⁻² at 550, 600, 650, and 700 °C, respectively with a 15 μm thick electrolyte. A relatively low cell interfacial polarization resistance of 0.132 Ω cm² at 700 °C indicated that the PBSC-BZCY could be a good cathode candidate for intermediate temperature SOFCs with BZCY electrolyte.     

Electrical conductivity and oxygen permeability of Ce0.8Sm0.2O2−δ–PrBaCo2O5+δ dual-phase composites

A novel dual-phase oxygen permeation membrane based on ion-conducting Ce_0.8Sm_0.2O_2−δ (SDC) and mixed conducting PrBaCo₂O_5+δ (PBCO) is presented. There is no obvious reaction between the two phases under preparation and oxygen permeation conditions. The percolative network of mixed conducting phase PBCO can be formed in SDC-PBCO composite when the ratio of PBCO is not less than 40 vol.%. Above this threshold, the oxygen permeability of SDC-PBCO membrane increases with increasing SDC content. Compared with pure PBCO membrane, the oxygen permeability of percolative SDC-PBCO composites is improved due to the 3D diffusion ability of SDC, which can shorten the tortuosity of the oxygen diffusion path in layered PBCO. The maximum oxygen flux based on 0.6-mm-thick SDC-PBCO (6/4) is 2.38 × 10⁻⁷ mol cm⁻² s⁻¹ at 925 °C. The dependence of the oxygen permeation flux on the membrane thickness demonstrates that the bulk diffusion is the limiting step at thickness higher than 0.8 mm and the surface exchange may play an important role when the thickness is below that. Incorporation of SDC into PBCO can not only improve the oxygen permeability but also enhance the structural stability. The SDC-PBCO (6/4) dual-phase membrane is a promising candidate for oxygen separation application.     

Novel layered perovskite SmBaCu2O5+δ as a potential cathode for intermediate temperature solid oxide fuel cells

A novel layered perovskite SmBaCu₂O_5+δ (SBCO) as a potential cathode for intermediate temperature solid oxide fuel cells (IT-SOFC) has been investigated in this paper. The SmBaCu₂O_5+δ oxide was synthesized by EDTA- Citrate complexing sol-gel process. The crystal structure, the thermal expansion, the electrical conductivity and electrochemical properties have been characterized by X-ray diffraction (XRD), dilatometer, four-probe dc method, electrochemical impedance spectroscopy (EIS) and cathodic polarization examinations. The average thermal expansion coefficient (TEC) of SBCO was 14.6 × 10⁻⁶/ °C in the temperature range of 50-800 °C, which matched Sm-doped ceria (SDC) electrolytes. The electrode polarization resistance was 0.469 Ωcm². Considering low thermal expansions and good electrochemical properties, layered perovskite SBCO shows promising performance as cathode material for IT-SOFCs.     

Preparation and properties of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ as novel oxygen electrode for reversible solid oxide electrochemical cell

In this work, double perovskite-type oxide PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ (PBSCF) is synthesized by the conventional wet chemical method and firstly characterized as the oxygen electrode for reversible solid oxide electrochemical cells (RSOCs). The microstructure and electrochemical performance of RSOCs based on this oxygen electrode are investigated. The maximum power density of the cell reaches 986 mW/cm² at 800 °C and the cell has good stability in short-term test in fuel cell (SOFC) mode. In electrolysis cell (SOEC) mode, it displays an electrolysis current density as high as 1.3 A/cm² when the temperature, absolute humidity (AH) and applied voltage are 800 °C, 50 vol % and 1.3 V, respectively. The cells also exhibit excellent durability of 120 h in SOEC mode and present good reversibility. The results suggest that the RSOCs based on this oxygen electrode has a very promising prospect.     

Structure-property relationship in layered perovskite cathode LnBa0.5Sr0.5Co2O5+δ (Ln = Pr, Nd) for solid oxide fuel cells

The layered cobaltites LnBa_0.5Sr_0.5Co₂O_5+δ (Ln = Pr, Nd) have been prepared by solid state reaction technique and structure-property relationships were investigated by means of neutron diffraction, ac impedance and dc conductivity measurements. Room temperature neutron diffraction shows the ordered distribution of oxygen vacancies in [PrO_δ] planes which doubles the lattice parameters from the perovskite cell parameter as a = b ≈ 2a_p, and c ≈ 2a_p (a_p is the cell parameter of the simple perovskite) yielding tetragonal symmetry in the P4/mmm space group. On heating, the oxygen vacancy ordering disappears and the structure can be defined as a = b ≈ a_p and c ≈ 2a_p in the same space group. Oxygen occupancies have been determined as a function of temperature from neutron diffraction. It was found that from 573 K to 973 K the total oxygen loss is about 0.265 O/formula unit and 0.366 O/formula unit for Pr and Nd containing materials, respectively. The oxygen occupancy decreases and cell volume increases with increasing temperature. Electrical conductivity measurements in air show that conductivity decreases with temperature, and at 873 K the conductivity is 493 S cm⁻¹ and 255 S cm⁻¹ for Pr and Nd containing samples, respectively. AC impedance measurements in symmetrical cell arrangement with CGO electrolyte shows that area specific resistance decreases with increasing temperature. At 873 K the ASR is 0.286 Ω cm² and 1.15 Ω cm² for Pr and Nd containing samples, respectively.     

Effect of firing temperature on the microstructure and performance of PrBaCo2O5+δ cathodes on Sm0.2Ce0.8O1.9 electrolytes fabricated by spray deposition-firing processes

The effect of firing temperature on the microstructure and performance of PrBaCo₂O_5+δ cathodes on Sm_0.2Ce_0.8O_1.9 electrolytes fabricated by spray deposition-firing processes is systematically studied by various characterization techniques. The grain size, porosity and particle connection of the electrode as well as the physical contact between the PrBaCo₂O_5+δ and Sm_0.2Ce_0.8O_1.9 layers are influenced differently by the firing temperature. The area specific resistances (ASRs) of the various PrBaCo₂O_5+δ cathodes are measured by electrochemical impedance spectroscopy in both symmetrical two-electrode and three-electrode configurations. The lowest ASR and cathode overpotential are achieved at a firing temperature of 1000 °C. Two main oxygen reduction reaction processes are proposed according to the oxygen partial pressure dependence of the electrode ASR. The rate-determining step is transmitted from a charge-transfer process at low firing temperatures to a non-charge-transfer process at high firing temperatures. A fuel cell with the PrBaCo₂O_5+δ cathode fired at an optimal temperature of 1000 °C delivers the attractive peak power density of 835 mW cm⁻² at 650 °C, while this density is much lower for other firing temperatures. This result suggests the firing temperature of PrBaCo₂O_5+δ electrodes should be carefully optimized for practical applications.     

Nanosized Ce0.8Sm0.2O1.9 infiltrated GdBaCo2O5+δ cathodes for intermediate-temperature solid oxide fuel cells

In this paper, Ce_0.8Sm_0.2O_1.9 (SDC) nanoparticles modified GdBaCo₂O_5+δ (GBCO) cathodes were fabricated by an infiltration technique and evaluated for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Good chemical compatibility between GBCO and infiltrated SDC was confirmed by X-ray diffraction (XRD) characterization. SDC nanoparticles (∼40 nm) formed continuous ionic-conducting phase on porous GBCO backbone, which contributed to significantly improved electro-catalytic property. At 600 °C, the composite cathode with 3.3 mg cm⁻² SDC loading exhibited encouragingly low R_p value of 0.1 Ω cm², which was much lower than 0.43 Ω cm² of pure-GBCO cathode. As revealed by PO₂ dependence of impedance spectra, the oxygen reduction reaction was mainly limited by charge-transfer processes. Furthermore, a stable operation of 80 h was obtained at 600 °C. Our study implies that infiltrated GBCO cathode is very attractive for application in IT-SOFC cathode.     

Electrochemical performance of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte based proton-conducting SOFC solid oxide fuel cell with layered perovskite PrBaCo2O5+δ cathode

BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb) exhibits adequate protonic conductivity as well as sufficient chemical and thermal stability over a wide range of SOFC operating conditions, while layered perovskite PrBaCo₂O_5+δ (PBCO) has advanced electrochemical properties. This research fully takes advantage of these advanced properties and develops a novel protonic ceramic membrane fuel cell (PCMFC) of Ni-BZCYYb|BZCYYb|PBCO. The performance of the button cell was tested under intermediate-temperature range from 600 to 700 °C with humified H₂ (∼3% H₂O) as fuel and ambient air as oxidant. The results show that the open circuit potential of 0.983 V and the maximal power density of 490 mW cm⁻² were achieved at 700 °C. By co-doping barium zirconate-cerate with Y and Yb, the conductivity of electrolyte was significantly improved. The polarization processes of the button cell were characterized using the complicated electrochemical impedance spectroscopy technique. The results indicate that the polarization resistances contributed from both charge migration processes and mass transfer processes increase with decreasing cell voltage loads. However the polarization resistance induced by mass transfer processes is negligible in the studied button cell.     

Assessment of PrBaCo2O5+δ + Sm0.2Ce0.8O1.9 composites prepared by physical mixing as electrodes of solid oxide fuel cells

The performance of PrBaCo₂O_5+δ + Sm_0.2Ce_0.8O_1.9 (PrBC + SDC) composites as electrodes of intermediate-temperature solid oxide fuel cells is investigated. The effects of SDC content on the performance and properties of the electrodes, including thermal expansion, DC conductivity, oxygen desorption, area specific resistance (ASR) and cathodic overpotential are evaluated. The thermal expansion coefficient and electrical conductivity of the electrode decreases with an increase in SDC content. However, the electrical conductivity of a composite electrode containing 50 wt% SDC reaches 150 S cm⁻¹ at 600 °C. Among the various electrodes under investigation, an electrode containing 30 wt% SDC exhibits superior electrochemical performance. A peak power density of approximately 1150 and 573 mW cm⁻² is reached at 650 and 550 °C, respectively, for an anode-supported thin-film SDC electrolyte cell with the optimal composite electrode. The improved performance of a composite electrode containing 70 wt% PrBC and 30 wt% SDC is attributed to a reduction in the diffusion path of oxygen-ions within the electrode, which is a result of a three-dimensional oxygen-ion diffusion path in SDC and a one-dimensional diffusion path in PrBC.     

Silver-modified Ba0.5Sr0.5Co0.8Fe0.2O3−δ as cathodes for a proton conducting solid-oxide fuel cell

Electrochemical performance of silver-modified Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF-Ag) as oxygen reduction electrodes for a protonic intermediate-temperature solid-oxide fuel cell (SOFC-H⁺) with BaZr_0.1Ce_0.8Y_0.1O₃ (BZCY) electrolyte was investigated. The BSCF-Ag electrodes were prepared by impregnating the porous BSCF electrode with AgNO₃ solution followed by reducing with hydrazine and then firing at 850 °C for 1 h. The 3 wt.% silver-modified BSCF (BSCF-3Ag) electrode showed an area specific resistance of 0.25 Ω cm² at 650 °C in dry air, compared to around 0.55 Ω cm² for a pure BSCF electrode. The activation energy was also reduced from 119 kJ mol⁻¹ for BSCF to only 84 kJ mol⁻¹ for BSCF-3Ag. Anode-supported SOFC-H⁺ with a BZCY electrolyte and a BSCF-3Ag cathode was fabricated. Peak power density up to 595 mW cm⁻² was achieved at 750 °C for a cell with 35 μm thick electrolyte operating on hydrogen fuel, higher than around 485 mW cm⁻² for a similar cell with BSCF cathode. However, at reduced temperatures, water had a negative effect on the oxygen reduction over BSCF-Ag electrode, as a result, a worse cell performance was observed for the cell with BSCF-3Ag electrode than that with pure BSCF electrode at 600 °C.     

Proton conducting solid oxide fuel cells with layered PrBa0.5Sr0.5Co2O5+δ perovskite cathode

BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) exhibits adequate protonic conductivity as well as sufficient chemical and thermal stability over a wide range of SOFC operating conditions, while layered perovskite PrBa_0.5Sr_0.5Co₂O_5+δ (PBSC) has advanced electrochemical properties. This research fully takes advantage of these advanced properties and develops a novel protonic ceramic membrane fuel cell (PCMFC) of Ni–BZCY7|BZCY7|PBSC. Experimental results show that the cell may achieve the open-circuit potential of 1.005 V, the maximal power density of 520 mW cm⁻², and a low electrode polarization resistance of 0.12 Ωcm² at 700 °C. Increasing operating temperature leads to the decrease of total cell resistance, among which electrolyte resistance becomes increasingly dominant over polarization resistance. The results also indicate that PBSC perovskite cathode is a good candidate for intermediate temperature PCMFC development, while the developed Ni–BZCY7|BZCY7|PBSC cell is a promising functional material system for SOFCs.     

Electrical conductivity,thermal expansion and electrochemical performances of Ba-doped SrCo0.9Nb0.1O3−δ cathodes for IT-SOFCs

Perovskite-type oxides Ba_xSr_1−xCo_0.9Nb_0.1O_3−δ (BSCNx, x = 0.0–0.8) were synthesized and investigated as cathodes for IT-SOFCs. Ba doping improves chemical compatibility between BSCNx oxides and Ce_0.9Gd_0.1O_1.95 (GDC) electrolyte. Effects of Ba doping on electrical conductivity, thermal expansion and electrochemical performances were systematically elucidated and discussed. Both thermal expansion coefficient (TEC) and polarization resistance (R_p) decrease with increasing Ba doping level up to x = 0.6, attain a minimum at x = 0.6 and then increase with further increasing x > 0.6. The decrease of TEC with the incorporation of Ba can be attributed to the weakened chemical expansion and the decrease of R_p with Ba is due to the increase of oxygen vacancy concentration and oxygen vacancy diffusion coefficient. With a 300 μm-thick GDC as electrolyte and BSCN0.6 as the cathode, the maximum power density of a single-cell achieves 778 mW cm⁻² at 800 °C. All these results indicate that the BSCN0.6 oxide is a promising cathode material for IT-SOFC.