Cathode Materials For IT-SOFCs Research Articles

Preparation of high-performance multiphase heterostructures IT-SOFC cathode materials by Pr-induced in situ assembly

Here, in situ assembly in La0.6Sr0.4Co0.2Fe0.8O3-δ and CoFe2O4 composite (LSCFC) cathode was induced by Pr to form La0.6Sr0.4CoxFeyO3-δ/PrCoO3/Co3O4/PrO2 (LSCFC-PI) multiphase heterostructures. The surface of LSCFC-PI forms uniform nanoparticles, and the unique core-shell structure prevents Sr segregation, thereby enhancing CO2 tolerance and increasing oxygen reduction reaction (ORR) active sites. Furthermore, compared with LSCFC, LSCFC-PI increases the oxygen vacancy content of the cathode due to the existence of multiphase heterostructure, improves the ORR kinetics, and the conductivity is also greatly improved. The peak power density (PPD) of LSCFC-PI as a single-cell cathode at 700 ℃ reached 1.51 W cm−2, which was 2.65 times higher than that of LSCFC's 0.57 W cm−2, and in the long-term stability test at a constant voltage ∼0.8 V for 100 hours, showing excellent stability. In situ assembly of multiphase heterostructures is expected to become a new strategy for developing high-performance IT-SOFC cathodes.

Evaluation of highly conductive cermet cathodes synthesized with organic chelating agents and sintered at low temperatures for IT-SOFCs

A novel semi-organic combustion approach using orange and lemon juice as chelating agents is employed to synthesize the perovskite Sr0.8X0.2Co0.2Fe0.8O3-δ (x = La, Ce) cathode for IT-SOFCs. This approach has been found to exhibit lower toxicity compared to chemical routes and lower impurities compared to green routes. The structural analysis validated the successful synthesis of perovskite Sr0.8X0.2Co0.2Fe0.8O3-δ (La, Ce) cathode materials with no prominent secondary phase of impurities while surface morphology revealed a porous and well-connected network of particles. EDS confirmed the composition and thermo-gravimetric analysis showed weight losses related to the creation of vacancies. The functional groups were investigated through FTIR and the conductivity measurements revealed higher electrical conductivity for Sr0.8X0.2Co0.2Fe0.8O3-δ (x = La, Ce) synthesized with orange juice as a chelating agent with Sr0.8La0.2Co0.2Fe0.8O3-δ exhibiting slightly higher value compared to Sr0.8Ce0.2Co0.2Fe0.8O3-δ. The electrochemical performance showed the highest power density of 354 and 313 mW·cm−2 at 700 °C obtained for cells having Sr0.8X0.2Co0.2Fe0.8O3-δ (x = La, Ce) cathodes synthesized with orange juice which was attributed to better crystallinity and uniform lattice. This work shows that a novel semi-organic route is successfully employed to synthesize the perovskite cathode materials for IT-SOFCs.

Fabrication and performance investigation of high entropy perovskite (Sr0.2Ba0.2Bi0.2La0.2Pr0.2)FeO3 IT-SOFC cathode material

The high-entropy oxide (HEO) concept expands the design space of solid oxide fuel cell (SOFC) cathode materials. There is great potential for the development of HEO cathode materials that has not been fully explored, and the relationship between their chemical composition, grain size, and electrochemical performance is not yet fully understood. This experimental design involved the preparation of single-phase perovskite (Sr0.2Ba0.2Bi0.2La0.2Pr0.2)FeO3 HEO SOFC cathode materials, and we systematically studied the effects of synthesis temperature and microstructure on their electrochemical performance. The results show that as the synthesis temperature increases, structural transformations from multiphase to single-phase perovskite HEO can be observed. It exhibits excellent conductivity and electrochemical performance (the minimum polarization resistance reaches 0.033 Ω∙cm2, and the maximum power density is 664 mW∙cm−2). The single-phase perovskite HEO sample exhibits higher electrochemical performances compared to those of multiphase perovskite. Furthermore, it exhibits outstanding ability to suppress Sr segregation, chemical compatibility with Ce0.8Sm0.2O1.9(SDC), and CO2 tolerance performance. The Distribution of relaxation time(DRT) analysis shows that as the synthesis temperature (1000–1150 ℃) increase, HEO single-phase formed and the oxygen atom reduction ability of the SBBLP samples was improved; and the adsorption of gas oxygen on the electrode surface is limited with porosity decreases. The work shows it is interesting and valuable to optimize the performance of SOFC cathode materials using a high entropy design.

Increasing thermodynamic stability and electrochemical performance of IT-SOFC cathodes based on Ln2MO4 (Ln = La, Pr; M = Ni, Cu)

La2-xPrxNi1-yCuyO4+δ (x = 0.5, 1, 1.5, y = 0.4, 0.6, 0.8) were synthesized by a citrate-nitrate method and studied as cathode materials for IT-SOFCs by Electrochemical Impedance Spectroscopy (EIS) in symmetrical cells based on the Ce0.8Sm0.2O2-δ (SDC) and La28-zW4+zO54+1.5z (z = 0.85, LWO) electrolytes. Phase identification and crystal structure analysis by means of X-ray powder diffraction (XRPD) shows that solubility of copper y decreases with the increase in praseodymium content x due to increasing structural distortions. Thermodynamic stability of La2-xPrxNi1-yCuyO4+δ at intermediate temperatures in air tends to decrease with praseodymium doping level x and increases with copper substitution for nickel y. Oxides with x = 0.5 and 0.6≤y ≤ 0.8 are shown to be thermodynamically stable at 700 °C in air. Electrochemical performance of the La2-xPrxNi1-yCuyO4+δ electrodes improves with praseodymium and copper doping. The results of EIS measurements at different temperatures and oxygen partial pressures (P(O2)) reveal that the rate-determining step of the overall electrochemical process is charge transfer, which can be a combination of surface diffusion and bulk diffusion. EIS studies in dry and wet air indicate the presence of proton conduction in the studied electrodes. The area-specific resistances (ASRs) for La2-xPrxNi1-yCuyO4+δ with x = 0.5, y = 0.6 and y = 0.8 in contact with SDC are comparable with those reported for Pr2NiO4+δ and equal to 0.07 and 0.065 Ω cm2 at 800 °C.

Electrochemical performance of Pr0.6Sr0.4Fe0.8Co0.2O3−δ as potential cathode material for IT-SOFC

Solid oxide fuel cells (SOFCs) are renowned for being effective energy sources that have potential to influence how energy is developed in future. SOFCs operate at low temperatures provides different benefits for widespread commercialization. In the present study a perovskite material Pr0.6Sr0.4Fe0.8Co0.2O3−δ (PSFCo) was investigated as cathode for SOFC in intermediate temperature range. Glycine nitrate process was used for the preparation of the samples. PSFCo exhibited cubic structure having small particle size (100–200 nm). The electrical conductivity of the PSFCo was measured as function of temperature up to 850 ℃. The sample displayed maximum electrical conductivity of 370 Scm−1 at around 550–600 ℃. The polarization behavior of PSFCo was calculated by means of AC impedance with Sm0.8Ce0.2O2 (SDC) as electrolyte. The value of area specific resistance (ASR) was calculated as 0.146 Ωcm2 at 800 ℃ and 0.248 Ωcm2 at 700 ℃.

Preparation of Pr, Co co-doped BaFeO3–δ-based nanofiber cathode materials by electrospinning

The solid oxide fuel cell (SOFC) is considered promising technology that directly converts the chemical energy stored in the fuel into electrical energy. However, the undesired oxygen reduction reaction (ORR) activity and stability of the cathode have hindered its commercialization. In this work, a series of Pr-doped PrxBa1-xFe0.8Co0.2O3-δ (x = 0∼0.3) nanofibers and powder cathode materials with excellent performance are synthesized by electrospinning and sol-gel methods, respectively. The influence of different Pr doping amounts on the nanofiber morphology, phase structure, thermal stability and electrochemical properties of BaFe0.8Co0.2O3-δ (BFCO) nanofibers cathode materials were investigated. Compared the microstructures and electrochemical performance of Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber and powders prepared by different methods. The partial substitution of Pr for Ba (doping of a few of Pr) can effectively eliminate the BFCO hexagonal phase and induce the transformation to the cubic phase. The content of oxygen vacancies was significantly increased as well as the cathode ORR activity was well enhanced. In addition, we demonstrated by DRT that oxygen adsorption is the rate-limiting step at the cathode. Among them, Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber has the best electrochemical performance and the highest oxygen surface exchange kinetics performance. The area-specific resistance (ASR) of Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber is 0.1416 Ω cm2 at 700 °C. When the peak power density (PPD) of the YSZ-NiO/YSZ/GDC/PBCF1–F single cell shows 0.787 W cm−2, an anode-supported fuel cell with Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber demonstrates excellent stability after 100 h of long-term stability test. Electrospinning technology is an effective method to prepare high-performance cathodes, and Pr0.1Ba0.9Fe0.8Co0.2O3-δ nanofiber cathodes are expected to be high-performance cathode materials for IT-SOFCs.

Sc-doped Co-based perovskites as IT-SOFC cathode with high oxygen reduction reaction and CO2 tolerance

The development of cathode materials with high oxygen reduction reaction (ORR) activity and stability in intermediate temperature (IT) environments is a key factor in the commercialization of solid oxide fuel cells (SOFC). In this paper, the ORR activity of the cathode is improved by doping high-valent Sc3+ ions at the B-site of the Sr0.5La0.5Co0.8Cu0.2-xScxO3–δ (x = 0, 0.02, 0.04), in which Sr0.5La0.5Co0.8Cu0.18Sc0.02O3–δ (SLCCS2) shows the best electrochemical performance, and the area-specific resistance of SLCCS2 at 700 °C is only 0.047 Ω cm2, much lower than the 0.087 Ω cm2 of Sr0.5La0.5Co0.8Cu0.2O3–δ (SLCC), and the peak power density of SLCCS2 reached 1.098 W cm−2, which is 1.84 times that of SLCC (0.598 W cm−2). In addition, SLCCS2 effectively reduces the thermal expansion coefficient, improves thermal matching with traditional electrolytes, and overcomes the problem of insufficient long-term SOFC stability caused by the high thermal expansion coefficient of Co-based perovskite to a certain extent. SLCCS2 also exhibits excellent CO2 tolerance. Considering comprehensively, SLCCS2 is expected to become an IT-SOFC cathode material with development potential.

Enhanced Compatibility and Activity of High-entropy Double Perovskite Cathode Material for IT-SOFC

Enhanced Compatibility and Activity of High-entropy Double Perovskite Cathode Material for IT-SOFC

SIFAT TERMAL, ELEKTROKIMIA DAN STRUKTUR MIKRO OKSIDA PEROVSKIT GANDA SEBAGAI MATERIAL KATODA SOFC BEROPERASI PADA SUHU MENENGAH

The oxides SmBa0.8Sr0.2Co2O5+δ (SBSC) have been explored as cathode materials for IT-SOFCs using SDC as the electrolyte. XRD was used to determine the structure of SBSC powder, and SEM was used to observe the morphology of the microstructure. Thermogravimetric Analysis (TGA) is used to measure the change in amount and rate in weight of SBSC cathode powder as a function of temperature in a controlled atmosphere. Symmetrical cells were tested using a potentiostat Voltalab PGZ 301. The weight loss of SBSC oxide during the heating temperature range between room temperature and 800 oC was 0.003%. Electrochemical impedance spectroscopy (EIS), low field (LF), and high field (HF) approaches are used to obtain activation energy (Ea) values of 99.77 kJ mol-1, 70.26 kJ mol-1, and 73.10 kJ mol-1. The Ea of polarization resistance (Rp) for the SBSC cathode reaches 104.59 kJ mol-1. The well-connected cathode-electrolyte contact determines the low resistance, and the SBSC cathode particle size is consistently dispersed in the interval of 1-1.5 µm.

Tuning Cu-Content La1-xSrxNi1-yCuyO3-δ with Strontium Doping as Cobalt-Free Cathode Materials for High-Performance Anode-Supported IT-SOFCs.

Cu-content La1-xSrxNi1-yCuyO3-δ perovskites with A-site strontium doping have been tuned as cobalt-free cathode materials for high-performance anode-supported SOFCs, working at an intermediate-temperature range. All obtained oxides belong to the R-3c trigonal system, and phase transitions from the R-3c space group to a Pm-3m simple perovskite have been observed by HT-XRD studies. The substitution of lanthanum with strontium lowers the phase transition temperature, while increasing the thermal expansion coefficient (TEC) and oxygen non-stoichiometry δ of the studied materials. The thermal expansion is anisotropic, and TEC values are similar to commonly used solid electrolytes (e.g., 14.1 × 10-6 K-1 for La0.95Sr0.05Ni0.5Cu0.5O3-δ). The oxygen content of investigated compounds has been determined as a function of temperature. All studied materials are chemically compatible with GDC-10 but react with LSGM and 8YSZ electrolytes. The anode-supported SOFC with a La0.95Sr0.05Ni0.5Cu0.5O3-δ cathode presents an excellent power density of 445 mW·cm-2 at 650 °C in humidified H2. The results indicate that La1-xSrxNi1-yCuyO3-δ perovskites with strontium doping at the A-site can be qualified as promising cathode candidates for anode-supported SOFCs, yielding promising electrochemical performance in the intermediate-temperature range.

Basic properties of low thermal expansion coefficient (Y0.5Ca0.5)1−xInxBaCo3ZnO7+δ (x=0, 0.1, 0.2, 0.3) solid solutions for solid oxide fuel cell cathode materials

• A series of YCI x BCZ cathodes have been studied systematically. • Thermal expansion coefficients of YCI x BCZ are lower than some cobalt-containing cathodes. • The YCI x BCZ cathodes show active catalysis on oxygen reduction reaction. • The YCI 0.2 BCZ cathode displays excellent phase stability and CO 2 tolerance. In this investigation, In-doped (Y 0.5 Ca 0.5 ) 1−x In x BaCo 3 ZnO 7+δ (x=0, 0.1, 0.2, and 0.3, abbreviated as YCI x BCZ) swedenborgite oxides are successfully prepared, and the effects of In-doping on phase structure, electrical conductivity, TEC, thermal stability and electrochemical properties are investigated thoroughly. The partial substitution of In for Y and Ca has a slight effect on the phase structure, electrical conductivity, TEC and area-specific resistance (ASR) of YCI x BCZ. All the YCI x BCZ samples investigated show an excellent tolerance to CO 2 at 800 °C. Additionally, the YCI 0.2 BCZ phase are stable after 72 h exposure to air at 600, 700, and 800 °C, separately, while YCI x BCZ (x=0, 0.1 and 0.3) show instability at 700 °C in air. The optimal composition, YCI 0.2 BCZ, exhibits a relatively low ASR value (0.048 Ω cm 2 at 800°C) and a high power density (345 mW cm −2 at 800°C). The current results demonstrate that YCI 0.2 BCZ is promising cathode material for IT-SOFCs.

Enhanced Performance of La0.8Sr0.2FeO3-δ-Gd0.2Ce0.8O2-δ Cathode for Solid Oxide Fuel Cells by Surface Modification with BaCO3 Nanoparticles.

Recently, Fe-based perovskite oxides, such as Ln1-xSrxFeO3-δ (Ln = La, Pr, Nd, Sm, Eu) have been proposed as potential alternative electrode materials for solid oxide fuel cells (SOFCs), due to their good phase stability, electrocatalytic activity, and low cost. This work presents the catalytic effect of BaCO3 nanoparticles modified on a cobalt-free La0.8Sr0.2FeO3-δ-Gd0.2Ce0.8O2-δ (LSF-GDC) composite cathode at an intermediate-temperature (IT)-SOFC. An electrochemical conductivity relaxation investigation (ECR) shows that the Kchem value of the modified LSF-GDC improves up to a factor of 17.47, demonstrating that the oxygen reduction process is effectively enhanced after surface impregnation by BaCO3. The area-specific resistance (ASR) of the LSF-GDC cathode, modified with 9.12 wt.% BaCO3, is 0.1 Ω.cm2 at 750 °C, which is about 2.2 times lower than that of the bare cathode (0.22 Ω.cm2). As a result, the anode-supported single cells, with the modified LSF-GDC cathode, deliver a high peak power density of 993 mW/cm2 at 750 °C, about 39.5% higher than that of the bare cell (712 mW/cm2). The single cells based on the modified cathode also displayed good performance stability for about 100 h at 700 °C. This study demonstrates the effectiveness of BaCO3 nanoparticles for improving the performance of IT-SOFC cathode materials.

“Influence of co-doping on structural, morphological, and electrical properties of Ruddlesden-Popper-type [formula omitted] as a cathode material for IT-SOFC”

For electric power generation Solid Oxide Fuel Cells (SOFCs) is the promising technology. Ruddlesden Popper type rare earth Nickelates have shown better performance as cathode with various electrolytes such as SDC and YSZ and possess high catalytic activity for ORR at intermediate temperature range of SOFCs. In the present work, samarium strontium nickelate SmSrNiO4-δ and co-doped (Sm0.95La0.05Sr0.95Ca0.05NiO4-δ) were synthesized by solid state route reaction method. The phase purity of samples is determined by X-ray Powder diffraction method and further confirmed by Rietveld refinement which was performed by using FULLPROF suite with I4/mmm symmetry and space group (139) and χ2 lies appreciably within the experimental errors. Further XRD confirms the single tetragonal phase which does not change with the co-substitution. The porous microstructure has been observed for all the studied samples. The micrograph shows that the average grain size increases with the co-substitution. The conductivity is observed to increase nearly-two folds with the co-substitution as compared to the parent sample. However, the oxygen reduction reaction is nearly same for both the samples.

Design of solid oxide structure on the composite cathode for IT-SOFC

Solid oxide structure of the cobalt-free composite has been exploited as a new cathode material for IT-SOFCs. The composite model system was synthesized using the metallic oxide material, which was formed by a solid-state reaction technique. The generation of the Sm0.5Sr0.25Ba0.25FeO3-δ (SSBF) model system was carried out during the sintering process. The weight loss and oxygen content were investigated by thermal gravimetric analysis (TG). Meanwhile, X-ray diffraction characterized the structure of the composite and thermal conductivity tested the conductivity properties. The results showed that the structure of the SSBF composite demonstrated the perovskite single phase leading to the structural design. The decomposition and evaporation of the constituent elements of the composite corresponded to weight losses during the constructing process. The oxygen content of the model system was 2.98 after the calcination process. The electrical conductivity value reached 2 S cm-1 at 400 °C and increases to a maximum of 7.5 S cm-1 at 710 °C. The metallic element played to generating the conductive behavior at the low temperature, while the ionic structure acted as elevated temperature. So, mixed ionic and electric conductors (MIEC) were employed comprehensively for creating the conductive properties. Based on the structure and conductivity results, the SSBF composite has a good chance as an alternative cathode material with a perovskite single phase for future TI-SOFCs applications

Copper doped SrFe0.9-Cu W0.1O3- (x = 0–0.3) perovskites as cathode materials for IT-SOFCs

Cu doped SrFe0.9-xCuxW0.1O3-δ (x = 0, 0.1, 0.2 and 0.3) perovskites were investigated as SOFC cathode materials. The effects of Cu doping on properties of SFCW samples were studied systematically. The oxygen content (3-δ) decreased by Cu doping, which leading to the decrement of electrical conductivity and the increment of TECs of SFCW samples. The ASR first decreases with x from 0 to 0.2 and then it increases when x up to 0.3. The ASR values are 0.161, 0.134, 0.102 and 0.117 Ω cm2 at 800 °C for SFCW samples with x = 0, 0.1, 0.2 and 0.3, respectively. The corresponding activation energy are 0.90, 0.88, 0.78 and 0.86 eV. The lowest ASR and activation energy for ORR of SFCW2 is a result from the joint effects of electrical conductivity, oxygen vacancy concentration and thermal expansion caused by Cu doping. The research results obtained in this study suggesting SFCW2 is a good cathode candidate for SOFC.

Combinatorial Development of LSF Based Cathode Material for IT-SOFC

The primary challenges for the commercialization of the technology are considered to be costs and durability. To accommodate this, research is pushing towards lower cell operation temperature (intermediate temperature SOFC, IT-SOFC) in the range of 500–700 0C [1,2]. The lower temperatures involve advantages such as wider and cheaper choice of materials (e.g. metals), increased material durability, and increased system stability.The progress in this field is, inevitably associated with a continuous search for novel cathode and anode materials having superior electrocatalytic activity in the intermediate-temperature range. These developments have also a key importance for other solid-state electrochemical devices, such as electrolyzer of carbon dioxide and water vapor [3].The fact that oxygen reduction rate is faster at the interface ,necessitates cathodes to be considered as composite. In this context, the traditional method is to mix cathode with electrolyte. This approach allows oxygen to be reduced at the interface and transported at the same time. Mixing cathode with electrolyte allows us to adjust the thermal expansion coefficient of the cathode. Another benefit of this approach is better bonding between the cathode and the electrolyte. Experimental The aim is to find the best cathode composition as a mixture of (La0.5Sr0.5)MnO3-δ (LSM), (La0.8Sr0.2)FeO3-δ (LSF) and (Zr10.92Sc0.08)O2- δ (8ScSZ) for IT-SOFC. In this study LSM, LSF and ScSZ targets were sputtered on both sides of Zr10.92Sc0.08 O2- δ electrolyte to form symmetric cells. We obtained 21 cells at the same time each with a different cathode composition. Geometry of targets and substrate is given in figure 1.Figure 1.Target and substrate geometriesThe produced cells were structurally characterized with XRD and SEM. Electrochemical performance of cells were determined using electrochemical impedance spectroscopy. The target working temperature is 600 0C and area specific resistance is maximum 0.15 ohm.cm2.

An analysis of SmBa0.5Sr0.5Co2O5+δ double perovskite oxide for intermediate–temperature solid oxide fuel cells

The main obstacle to solid oxide fuel cells (SOFCs) implementation is the high operating temperature in the range of 800–1,000 °C so that it has an impact on high costs. SOFCs work at high temperatures causing rapid breakdown between layers (anode, electrolyte, and cathode) because they have different thermal expansion. The study focused on reducing the operating temperature in the medium temperature range. SmBa0.5Sr0.5Co2O5+δ (SBSC) oxide was studied as a cathode material for IT-SOFCs based on Ce0.8Sm0.2O1.9 (SDC) electrolyte. The SBSC powder was prepared using the solid-state reaction method with repeated ball-milling and calcining. Alumina grinding balls are used because they have a high hardness to crush and smooth the powder of SOFC material. The specimens were then tested as cathode material for SOFC at intermediate temperature (600–800 °C) using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), electrochemical, and scanning electron microscopy (SEM) tests. The X-ray powder diffraction (XRD) pattern of SBSC powder can be indexed to a tetragonal space group (P4/mmm). The overall change in mass of the SBSC powder is 8 % at a temperature range of 125–800 °C. A sample of SBSC powder showed a high oxygen content (5+δ) that reached 5.92 and 5.41 at temperatures of 200 °C and 800 °C, respectively. High diffusion levels and increased surface activity of oxygen reduction reactions (ORRs) can be affected by high oxygen content (5+δ). The polarization resistance (Rp) of samples sintered at 1000 °C is 4.02 Ωcm2 at 600 °C, 1.04 Ωcm2 at 700 °C, and 0.42 Ωcm2 at 800 °C. The power density of the SBSC cathode is 336.1, 387.3, and 357.4 mW/cm2 at temperatures of 625 °C, 650 °C, and 675 °C, respectively. The SBSC demonstrates as a prospective cathode material for IT-SOFC

Evaluation of perovskite oxides LnBaCo2O5+δ (Ln = La, Pr, Nd and Sm) as cathode materials for IT-SOFC

The structural characterization, surface state and electrochemical performances of LnBaCo2O5+δ (LnBC) (Ln = La, Pr, Nd and Sm) perovskite cathode are systematically investigated for intermediate-temperature solid oxide fuel cells. The structural symmetry gradually distorts with the reduced ionic radius. The electrical conductivity decreases due to the increasing oxygen vacancy concentration from La to Sm. X-ray photoelectron spectroscopy analysis indicates that the concentration of oxygen active sites on the surface of LnBC samples decreases with shrinking Ln3+ radius. The increasing Ln–O bond energy leads to the reduction of the thermal expansion coefficients. The electrochemical performance of LnBC electrode decreases with the decreasing Ln3+ ionic radius. This result may be related to the decreasing.

Novel cobalt-free Pr2Ni1-xNbxO4 (x = 0, 0.05, 0.10, and 0.15) perovskite as the cathode material for IT-SOFC

The cobalt-free cathode materials with high activity is critical to the commercial application of medium temperature solid oxide fuel cells (IT-SOFC). Herein, a series of cobalt-free Nb-doped Pr2Ni1-xNbxO4 (x = 0, 0.05, 0.10, and 0.15) perovskite oxides were successfully prepared, and the effects of Nb-doping on the structure, thermal stability and electrochemical properties of the cathode material are studied in detail. The Pr2Ni1-xNbxO4 exhibits a K2NiF4 type structure with Fmmm space group. The Nb5+ cations that doped into Pr2NiO4 replaces the Ni site, which increases the surface oxygen content, then effectively eliminates the phase transition of Pr2NiO4 and significantly improves the ORR catalytic activity. The Pr2Ni0.9Nb0.1O4 was found to occupy the lowest polarization resistance of 0.057 Ω cm2, and the peak power density of single cells supported by the electrolyte is 0.576 W cm−2 at 700 °C, which has good long-term stability.

Characterization and functional application of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ cathode material for IT-SOFC

The physicochemical properties for layered perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) oxide are systematically investigated to gain insight into the correlation between structure, surface state and oxygen reduction reaction properties. The PBSCF sample possesses orthorhombic structure and keeps better structural stability under operating conditions. X-ray photoelectron spectra analysis indicates that the mixed oxidation state of (Co, Fe) and Pr promotes the oxygen reduction reaction kinetics by creating oxygen vacancies at the surface. Mössbauer Spectroscopy affirms that the proportion of Fe3+ and Fe4+ in iron species is 79.1 % and 20.9 %, respectively. The electrode polarization resistance is 0.067 Ω cm2 at 800 °C in air. The oxygen-ion bulk diffusion plays the rate-limiting step during the electrode process. The cell with PBSCF cathode delivers the power density of 590 mW cm−2 at 800 °C. These results show the PBSCF exhibits a promising application prospect in intermediate temperature solid oxide fuel cell.