PrBa0.5Sr0.5Co2O5+x as cathode material based on LSGM and GDC electrolyte for intermediate-temperature solid oxide fuel cells

PrBa_0.5Sr_0.5Co₂O_5+x (PBSC) oxides have been evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ce_0.9Gd_0.1O_1.95 (GDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolytes. XRD results show that PBSC cathode is chemically compatible with the intermediate-temperature electrolyte materials GDC and LSGM. The maximum electrical conductivity is 1522 S cm⁻¹ at 100 °C and its value is higher than 581 S cm⁻¹ over the whole temperature range investigated. Microstructures show that the contact between PBSC and LSGM is better than that between PBSC and GDC. The area-specific resistances (ASRs) of PBSC cathode on GDC and LSGM electrolytes are 0.048 and 0.027 Ωcm² at 800 °C, respectively. The electrolyte-supported (thickness of electrolyte is 300 μm) fuel cells generate good performance with the maximum power densities of 617 mW cm⁻² on GDC electrolyte and 1021 mW cm⁻² on LSGM electrolyte at 800 °C. All results demonstrate that PBSC oxide is a very promising cathode material for application in IT-SOFCs and this cathode based on LSGM electrolyte obtained better performance than on GDC electrolyte.     

Novel YBaCo3.2Ga0.8O7+δ as a cathode material and performance optimization for IT-SOFCs

The YBaCo_3.2Ga_0.8O_7+δ (YBCGO) oxide has been developed as new cathode material based on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity of YBCGO sample reaches 1.4–2.1 S cm⁻¹ in the temperature range 650–800 °C. The thermal expansion coefficient (TEC) value of YBCGO is 8.6 × 10⁻⁶ K⁻¹ in the range of 30–1000 °C. The area specific resistance (ASR) of a YBCGO cathode with LSGM electrolyte is 0.111 Ω cm² at 800 °C and it decreases to 0.047 Ω cm² when PrBaCo₂O_5+δ (PBCO) is added to form a YBCGO–PBCO composite cathode. Peak power densities of single cells using a pure YBCGO cathode and a YBCGO–PBCO composite cathode are 395 and 531 mW cm⁻² at 800 °C, respectively. The results of this study demonstrate that YBCGO can be a promising cathode material for IT-SOFCs.     

SmBaCo2O5+x double-perovskite structure cathode material for intermediate-temperature solid-oxide fuel cells

SmBaCo₂O_5+x (SBCO), an oxide with double-perovskite structure, has been developed as a novel cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The electrical conductivity of an SBCO sample reaches 815–434 S cm⁻¹ in the temperature range 500–800 °C. XRD results show that an SBCO cathode is chemically compatible with the intermediate-temperature electrolyte materials Sm_0.2Ce_0.8O_1.9 (SDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM). The polarization resistances of an SBCO cathode on SDC and LSGM electrolytes are 0.098 and 0.054 Ω cm² at 750 °C, respectively. The maximum power densities of a single cell with an SBCO cathode on SDC and LSGM electrolytes reach 641 and 777 mW cm⁻² at 800 °C, respectively. The results of this study demonstrate that the double-perovskite structure oxide SBCO is a very promising cathode material for use in IT-SOFCs.     

Cobalt-free Sr0.7Y0.3CuO2+δ as a cathode for intermediate-temperature solid oxide fuel cell

Cobalt-free oxide Sr_0.7Y_0.3CuO_2+δ (SYCu) with one-dimensional structure has been investigated as potential cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. The crystal structure, chemical compatibility, thermal expansion and electrochemical performance were examined by X-ray diffraction technique, electrochemical workstation and thermal dilatometer. One-dimensional structure Sr_1−xY_xCuO_2+δ and Sr_2−xY_xCuO_3+δ phases appeared as the main parts after calcination above 900 °C. The copper based oxide SYCu showed a thermal expansion coefficient (TEC) about 11.1 × 10⁻⁶/°C at 25–800 °C, exhibiting good physical compatibility with samarium doped cerium (SDC) electrolyte. High electro-catalytic performance was obtained for SYCu cathode in a symmetrical cell with a polarization resistance (R_p) of 0.029 Ω cm² and an overpotential of 4.9 mV at 100 mA/cm² at 800 °C, showing great promising use as cathode materials for IT-SOFCs. In addition, the polarization resistance of SYCu cathode remain constant after operation at 800 °C for 100 h, showing excellent long-term stability at operation temperature.     

Characterization of SmBaCoFeO5+δ−Ce0.9Gd0.1O1.95 composite cathodes for intermediate-temperature solid oxide fuel cells

The performance of SmBaCoFeO_5+δ (SBCF)–xCe_0.9Gd_0.1O_1.95 (GDC) (x = 0, 10, 30, 50, 60, wt%) composite cathodes has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion coefficient (TEC) and electrochemical property measurements are employed to study the materials. The XRD results prove that there is no serious reaction between SBCF and GDC oxides even at 1000 °C. The thermal expansion behavior shows that the TEC value of SBCF cathode decreases greatly with GDC addition. The addition of GDC to SBCF cathode further reduces the polarization resistance. The lowest polarization resistance of 0.036 Ω cm² is achieved at 800 °C for SBCF–50GDC composite cathode. An electrolyte-supported fuel cell is prepared using SBCF–50GDC as cathode and NiO–GDC (65:35 by weight) as anode. The cell generates good performance with the maximum power density of 691 mW cm⁻², 503 mW cm⁻² and 337 mW cm⁻² at 800 °C, 750 °C and 700 °C, respectively. Preliminary results indicate that SBCF–50GDC is especially promising as a cathode for IT-SOFCs.     

Performances of SmBaCoCuO5+δ–Ce0.9Gd0.1O1.95 composite cathodes for intermediate-temperature solid oxide fuel cells

SmBaCoCuO_5+δ–xCe_0.9Gd_0.1O_1.95 (SBCCO–xGDC, x = 10, 30, 50, 60, wt%) composite cathodes have been investigated for their potential utilization in intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion behavior shows that the thermal expansion coefficient (TEC) values of SBCCO cathode decrease with GDC addition. The TEC of SBCCO–50GDC cathode is 13.1 × 10⁻⁶ K⁻¹ from 30 to 850 °C in air. By means of DC polarization and AC impedance spectroscopy, the electrochemical performance of SBCCO–xGDC composite cathodes on GDC electrolyte is examined. Results indicate that the proper addition of GDC could improve the performance of SBCCO cathode. The optimum content of GDC in the composite cathodes is 50 wt% with the polarization resistance (R_p) of 0.040 Ω cm² at 800 °C. An electrolyte-supported single-cell configuration of SBCCO–50GDC/GDC/Ni–GDC attains a maximum power density of 628 mW cm⁻² at 800 °C. Preliminary results indicate that SBCCO–50GDC is especially promising as a cathode for IT-SOFCs.     

SrCo0.7Fe0.2Ta0.1O3−δ perovskite as a cathode material for intermediate-temperature solid oxide fuel cells

Perovskite oxide SrCo_0.7Fe_0.2Ta_0.1O_3−δ (SCFT) was synthesized by a solid–state reaction and investigated as a potential cathode material for intermediate-temperature solid oxide fuel cell (IT-SOFC). The single phase SCFT having a cubic perovskite structure was obtained by sintering the sample at 1200 °C for 10 h in air. Introduction of Ta improved the phase stability of SCFT. The SCFT exhibited a good chemical compatibility with the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte at 950 °C for 10 h. The average thermal expansion coefficient was 23.8 × 10⁻⁶ K⁻¹ between 30 and 1000 °C in air. The electrical conductivities of the SCFT sample were 71–119 S cm⁻¹ in the 600−800 °C temperature range in air, and the maximum conductivity reached 247 S cm⁻¹ at 325 °C. The polarization resistance of the SCFT cathode on the LSGM electrolyte was 0.159 Ω cm² at 700 °C. The maximum power density of a single-cell with the SCFT cathode on a 300 μm-thick LSGM electrolyte reached 652.9 mW cm⁻² at 800 °C. The SCFT cathode had shown a good electrochemical stability over a period of 20 h short-term testing. These findings indicated that the SCFT could be a suitable alternative cathode material for IT-SOFCs.     

Electrochemical performances of NdBa0.5Sr0.5Co2O5+x as potential cathode material for intermediate-temperature solid oxide fuel cells

Layered perovskite oxide NdBa_0.5Sr_0.5Co₂O_5+x is investigated as a cathode material for intermediate-temperature solid oxide fuel cells. The NBSC cathode is chemically compatible with the electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) at temperatures below 1000 °C. It is metallic in nature and the maximum and minimum conductivities are 1368 S cm⁻¹ at 100 °C and 389 S cm⁻¹ at 850 °C. The area specific resistance (ASR) value for the NBSC cathode is as low as 0.023 Ω cm² at 850 °C. The electrolyte-supported fuel cell generates good performance with the maximum power density of 904, 774 and 556 mW cm⁻² at 850, 800 and 750 °C, respectively. Preliminary results indicate that NBSC is promising as a cathode for IT-SOFCs.     

Preparation and characterization of new cobalt-free cathode Pr0.5Sr0.5Fe0.8Cu0.2O3−δ for IT-SOFC

A new cobalt-free perovskite oxide Pr_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ (PSFC) has been synthesized and evaluated as cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The chemical compatibility of PSFC with Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte has be proven by XRD, and its electrical conductivity reaches the maximum value of 264.1 S cm⁻¹ at 475 °C. Symmetrical cells with the configuration of PSFC/SDC/PSFC are used for the impedance study and the polarization resistance (Rp) of PSFC cathode is as low as 0.050 Ω cm² at 700 °C. Single cells, consisting of Ni–YSZ/YSZ/SDC/PSFC structure, are assembled and tested from 550 °C to 800 °C with wet hydrogen (∼3% H₂O) as fuel and static air as oxidant. A maximum power density of 1077 mW cm⁻² is obtained at 800 °C. All the results suggest that the cobalt-free perovskite oxide PSFC is a very promising cathode material for application in IT-SOFC.     

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.     

Synthesis and properties of Sm-deficient Sm1−xBaCo2O5+δ perovskite oxides as cathode materials

Double-layered perovskite oxides of Sm_1−xBaCo₂O_5+δ (S_1−xBCO) with various A-site Sm³⁺-deficiencies (x = 0.00–0.08) were synthesized and evaluated as cathode materials of intermediate-temperature solid oxide fuel cells (IT-SOFCs). The Sm³⁺-deficiency content in S_1−xBCO was limited up to x = 0.05, and higher content x = 0.08 caused impurity phase. S_1−xBCO oxides were chemically stable with GDC electrolyte at 1050 °C and below. Introduction of Sm³⁺-deficiency caused decreased oxygen content and increased concentration of oxygen vacancy in S_1−xBCO. Electrical conductivities of S_1−xBCO decreased with increasing temperature in air, and also changed with the Sm³⁺-deficiency content. Electrochemical performance of S_1−xBCO cathodes were characterized by impedance spectra measurement based on symmetric cells. Higher Sm³⁺ deficiency content has resulted in decreased area specific resistances (ASRs) and activation energy (Ea), i.e. enhanced electrochemical reaction reactivity for the S_1−xBCO cathodes. Among the studied samples, the S_0.95BCO (x = 0.05) oxide showed the best electrochemical performance with ASR values of 0.316 Ω cm² at 600 °C, 0.137 Ω cm² at 650 °C, 0.068 Ω cm² at 700 °C and 0.038 Ω cm² at 750 °C respectively, thus it's a promising cathode material of IT-SOFCs.     

Electrochemical behavior of Ba0.5Sr0.5Co0.2−xZnxFe0.8O3−δ (x = 0-0.2) perovskite oxides for the cathode of solid oxide fuel cells

Zinc-doped barium strontium cobalt ferrite (Ba_0.5Sr_0.5Co_0.2−xZn_xFe_0.8O_3−δ (BSCZF), x = 0, 0.05, 0.1, 0.15, 0.2) powders with various proportions of zinc were prepared using the ethylenediamine tetraacetic acid (EDTA)-citrate method with repeated ball-milling and calcining. They were then evaluated as cathode materials for solid oxide fuel cells at intermediate temperatures (IT-SOFCs) using XRD, H₂-TPR, SEM, and electrochemical tests. By varying the zinc doping (x) from zero to 0.2 (as a substitution for cobalt which ranged from zero to 100%), it was found that the lowest doping of 0.05 (BSCZF05) resulted in the highest electrical conductivity of 30.7 S cm⁻¹ at 500 °C. The polarization resistances of BSCZF05 sintered at 950 °C were 0.15 Ω cm², 0.28 Ω cm² and 0.59 Ω cm² at 700 °C, 650 °C and 600 °C, respectively. The resistance decreased further by about 30% when Sm_0.2Ce_0.8O_2−δ (SDC) electrolyte particles were incorporated and the sintering temperature was increased to 1000 °C. Compared to BSCF without zinc, BSCZF experienced the lowest decrease in electrochemical properties when the sintering temperature was increased from 950 °C to 1000 °C. This decrease was due to an increase in thermal stability and a minimization in the loss of some cobalt cations without a decrease in the electrical conductivity. Using a composite cathode of BSCZF05 and 30 wt.% of SDC, button cells composed of an Ni-SDC support with a 30 μm dense SDC membrane exhibited a maximum power density of 605 mW cm⁻² at 700 °C.     

Synthesis of nanostructured BSCF by oxalate co-precipitation – As potential cathode material for solid oxide fuels cells

Ba_xSr_1−xCo_yFe_1−yO₃ (BSCF) cathode material for solid oxide fuel cells (SOFC) was synthesized in nanocrystalline form by a novel chemical alloying approach. Thermodynamic modeling has been performed using Medusa software for obtaining the optimum conditions for the fabrication of a precursor with the desired composition. Precursor powder was then calcined and annealed to produce the final mixed oxide BSCF composition. The thermal properties, phase constituents, microstructure and elemental analysis of the samples were characterized by TGA, XRD, SEM and EDS techniques respectively. Spark Plasma Sintering (SPS) has been used at 1080 °C and under 50 MPa pressure to obtain the pellets of BSCF with preserved nanostructure and rather high compaction density for electrical conductivity measurements. The results show that the powders have cubic perovskite-type structure with a high homogeneity. Finer resultant powder, compared to earlier reports, and SPS sintered BSCF with nanosized grains exhibited a significantly higher electrical conductivity up to 900 °C. Specific conductivity values have been measured in air and N₂ and the maximum of 63 S cm⁻¹ at 430 °C in air and 25 S cm⁻¹ at 375 °C in N₂ correspondingly show twice as much as conventional BSCF implying a high pledge for nano-BSCF as cathode material in intermediate-temperature SOFC. This is due to the lower interfacial resistance of preserved nanograins by the use of SPS sintering. Presented co-precipitation method is easy to handle and has a high promise to synthesize BSCF at large-scale for IT-SOFCs.     

Co-doped Sr2FeNbO6 as cathode materials for intermediate-temperature solid oxide fuel cells

Sr₂Fe_1−xCo_xNbO₆ (0.1 ≤ x ≤ 0.9) (SFCN) oxides with perovskite structure have been developed as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). These materials are synthesized via solid-state reaction and characterized by XRD, SEM, electrical conductivity, AC impedance spectroscopy and DC polarization measurements. The reactivity tests show that the Sr₂Fe_1−xCo_xNbO₆ electrodes are chemically compatible with the Zr_0.85Y_0.15O_1.925 (YSZ) and Ce_1.9Gd_0.1O_1.95 (CGO) electrolytes at 1200 °C, and the electrode forms a good contact with the electrolyte after sintering at 1200 °C for 12 h. The total electrical conductivity that has a considerable effect on the electrode properties is determined in a temperature range from 200 °C to 800 °C. The highest conductivity of 5.7 S cm⁻¹ is found for Sr₂Fe_0.1Co_0.9NbO₆ at 800 °C in air. The electrochemical performances of these cathode materials are studied using impedance spectroscopy at various temperatures and oxygen partial pressures. Two different kinds of reaction rate-limiting steps exist on the Sr₂Fe_0.1Co_0.9NbO₆ electrode, depending on the temperature. The Sr₂Fe_0.1Co_0.9NbO₆ electrode on CGO electrolyte exhibits a polarization resistance of 0.74 Ω cm² at 750 °C in air, which indicates that the Sr₂Fe_0.1Co_0.9NbO₆ electrode is a promising cathode material for IT-SOFCs.     

Preparation and electrochemical performance of Pr2Ni0.6Cu0.4O4 cathode materials for intermediate-temperature solid oxide fuel cells

Cathode material Pr₂Ni_0.6Cu_0.4O₄ (PNCO) for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is synthesized by a glycine-nitrate process using Pr₆O₁₁, NiO, and CuO powders as raw materials. X-ray diffraction analysis reveals that nanosized Pr₂Ni_0.6Cu_0.4O₄ powders with K₂NiF₄-type structure can be obtained from calcining the precursors at 1000 °C for 3 h. Scanning electron microscopy shows that the sintered PNCO samples have porous microstructure with a porosity of more than 30% and grain size smaller than 2 μm. A maximum conductivity of 130 S cm⁻¹ is obtained from the PNCO samples sintered at 1050 °C. A single fuel cell based on the PNCO cathode with 30 μm Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte film and a 1 mm NiO-SCO anode support is constructed. The ohmic resistance of the single Ni-SCO/SCO/PNCO cell is 0.08 Ω cm² and the area specific resistance (ASR) value is 0.19 Ω cm² at 800 °C. Cell performance was also tested using humidified hydrogen (3% H₂O) as fuel and air as oxidant. The single cell shows an open circuit voltage of 0.82 V and 0.75 V at 700 °C and 800 °C, respectively. Maximum power density is 238 mW cm⁻² and 308 mW cm⁻² at 700 °C and 800 °C, respectively. The preliminary tests have shown that Pr₂Ni_1−xCu_xO₄materials can be a good candidate for cathode materials of IT-SOFCs.     

Pr1.8La0.2Ni0.74Cu0.21Ga0.05O4+δ as a potential cathode material with CO2 resistance for intermediate temperature solid oxide fuel cell

Pr_1.8La_0.2Ni_0.74Cu_0.21Ga_0.05O_4+δ (PLNCG), a mixed ionic electron conductor (MIEC) with a K₂NiF₄-type structure, has been studied as a potential cathode material based on YSZ (ZrO₂ with 8 mol% Y₂O₃) electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). The X-ray diffraction (XRD) analysis reveals that the good chemical compatibility between the PLNCG and YSZ. The maximum electric conductivity of the PLNCG appeared at about 460 °C and the value was 32 S cm⁻¹ in air and 34 S cm⁻¹ in O₂, respectively. A hollow fiber SOFC was fabricated with the PLNCG as the cathode, NiO–YSZ (1:1; w/w) as the anode and YSZ as the electrolyte. The maximum power density of the cell is 876 mW cm⁻² and the corresponding polarization resistance of the cell is 0.41 Ω cm² at 750 °C. Furthermore, the PLNCG cathode shows an excellent CO₂ resistance in the operation temperature range. The maximum power density of the cell is similar to that when the cathode is exposed to air. Furthermore, the cell performance is stable when the CO₂ concentrations in the air vary from 0 to 10 vol.% at both 700 and 750 °C. These results indicate that the PLNCG can be a good candidate for CO₂ resistance cathode materials of IT-SOFCs based on YSZ electrolyte.     

Cobalt-free composite cathode for SOFCs: Brownmillerite-type calcium ferrite and gadolinium-doped ceria

A cobalt-free composite Ca₂Fe₂O₅ (CFO) – Ce_0.9Gd_0.1O_1.95 (GDC) is investigated as a new cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Gd_0.1Ce_0.9O_1.95 (GDC) electrolyte. The cathodes had brownmillerite structure with x wt.% Gd_0.1Ce_0.9O_1.95 (GDC) – (100−x) wt.% Ca₂Fe₂O₅ (CFO), where x = 0, 10, 20, 30 and 40. The effect of GDC incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the CFO–GDC composites is investigated. The composite cathode of 30 wt.% GDC – 70 wt.% CFO (CG30) coated on Gd_0.1Ce_0.9O_1.95 electrolyte showed the lowest area specific resistance (ASR), 0.294 Ω cm² at 700 °C and 0.122 Ω cm² at 750 °C. The TEC of the CG30 cathode was 13.1 × 10⁻⁶ °C⁻¹ up to 900 °C, which is a lower value than for CFO alone (13.8 × 10⁻⁶ °C⁻¹). Long-term thermal stability and thermal cycle testing of CG30 cathodes were performed. Stable ARS values were observed during both tests without delamination at the cathode–electrolyte interface. An electrolyte-supported single cell with a 300-μm-thick GDC electrolyte and an anode-supported single cell with ∼10-μm-thick yttria-stabilized zirconia (YSZ) with a GDC buffer layer attained maximum power densities of 395 mW cm⁻² at 750 °C and 842 mW cm⁻² at 800 °C, respectively. The unique composite composition of CG30 demonstrates enhanced electrochemical performance and good thermal stability for IT-SOFCs.     

Electrochemical performance of La2Cu1−xCoxO4 cathode materials for intermediate-temperature SOFCs

K₂NiF₄-type structure oxides La₂Cu_1−xCo_xO₄ (x = 0.1, 0.2, 0.3) are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The materials are characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. The results show that no reaction occurs between La₂Cu_1−xCo_xO₄ electrode and Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte at 1000 °C. The electrode forms good contact with the electrolyte after sintering at 800 °C for 4 h in air. The electrode properties of La₂Cu_1−xCo_xO₄ are studied under various temperatures and oxygen partial pressures. The optimum composition of La₂Cu_0.8Co_0.2O₄ results in 0.51 Ω cm² polarization resistance (R_p) at 700 °C in air. The rate limiting step for oxygen reduction reaction (ORR) is the charge transfer process. La₂Cu_0.8Co_0.2O₄ cathode exhibits the lowest overpotential of about 50 mV at a current density of 48 mA cm⁻² at 700 °C in air.     

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.     

Electrode redox properties of Ba1−xLaxFeO3−δ as cobalt free cathode materials for intermediate-temperature SOFCs

Cobalt-free perovskite oxides Ba_1−xLa_xFeO_3−δ (x = 0.1–0.4) were synthesized by glycine-nitrate combustion method and investigated as a candidate cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). Cubic perovskite structure was obtained when 10–20 mol% La was substituted at Ba-site in Ba_1−xLa_xFeO_3−δ, and the crystal structure was transformed from cubic structure into orthorhombic one at x ≥ 0.2 with an addition of lanthanum doping. The thermal expansion coefficients of Ba_1−xLa_xFeO_3−δ oxides decreased gradually with La content due to increasing electrostatic attraction forces. A gradual increase existed in electrical conductivity tendency with La content due to disproportionation of Fe³⁺ and the larger extent of electron clouds. The electrode redox performance was investigated by electrochemical impedance spectroscopy. Among Ba_1−xLa_xFeO_3−δ series oxides, Ba_0.9La_0.1FeO_3−δ exhibited the best electrochemical performance. The area specific resistance (ASR) of Ba_0.9La_0.1FeO_3−δ was 0.079 Ω cm², 0.37 Ω cm², and 2.15 Ω cm² at 800, 700 and 600 °C under open circuit potential. To investigate electrochemical performances after cathodic polarization, bias potentials were employed on Ba_1−xLa_xFeO_3−δ cathode at 650–800 °C. The results demonstrated the potential applications for Ba_0.9La_0.1FeO_3−δ as cathode materials for IT-SOFCs as a tradeoff between electrochemical and thermal expansion performance.