Cathode For Intermediate Temperature Solid Oxide Research Articles

Porous structured BaCo0.8Nb0.1Sc0.1O3-δ perovskite synthesized by template method as high performance cathode for intermediate-temperature solid oxide fuel cells

BaCoO3-δ is a potential cathode material because of its mixed ionic and electronic conducting. Unfortunately, the low symmetry structure and oxygen reduction activity of BaCoO3-δ has limited its application on solid oxide fuel cells. Porous structured BaCo0.8Nb0.1Sc0.1O3-δ cubic perovskite is synthesized by template method. The area specific resistance (ASR) of porous BaCo0.8Nb0.1Sc0.1O3–δ is 0.0257 Ω‧cm2 at 700 °C and the activation energy was only 126.8 kJ‧mol−1. The further study shows that the charge transfer process and adsorption-desorption of oxygen process jointly determine the rate-determining-step of porous BaCo0.8Nb0.1Sc0.1O3–δ.

Cobalt-free perovskite Ln0.5Sr0.5Fe0.8Cu0.2O3-δ (Ln = Pr, Nd, Sm, and Gd) as cathode for intermediate-temperature solid oxide fuel cell

Ln0.5Sr0.5Fe0.8Cu0.2O3-δ (LnSFC, Ln = Pr, Nd, Sm, Gd) perovskite oxide as a cobalt-free cathode was systematically evaluated for intermediate-temperature solid oxide fuel cell (IT-SOFC). XRD results show that PrSFC presents the cubic structure, while NdSFC, SmSFC, and GdSFC present an orthorhombic structure. The conductivity of the four samples is in accordance with the GdSFC < SmSFC < NdSFC < PrSFC relationship. AC impedance testing was performed using a symmetrical fuel cell of the structure LnSFC/Ce0.9Sm0.1O1.95(SDC)/LnSFC. The polarization resistance values of PrSFC, NdSFC, SmSFC, and GdSFC are 0.036, 0.089, 0.097, and 0.160 Ω cm2 at 800 °C, respectively. Then, SDC electrolyte-support single cell was fabricated and the power densities of PrSFC, NdSFC, SmSFC, and GdSFC cathodes were 364, 311, 254 and 104 mW cm−2, respectively, at 800 °C. Our preliminary experiment results show that LnSFC oxide meets the requirements of the electrode, and it can be a possible cathode for IT-SOFC.

Effective promotion of oxygen reduction activity by rare earth doping in simple perovskite cathodes for intermediate-temperature solid oxide fuel cells

The development of highly efficient cathode materials at intermediate temperatures is critical to realize the large-scale commercialization of solid oxide fuel cells (SOFCs). Here, a facile way is presented to tune both the crystal structure and the electrochemical performance of simple perovskite oxides as cathode materials by doping rare earth cations (La, Pr, Nd) in A site. The obtained cubic perovskites LnxBa1−xCo0.7Fe0.3O3−δ (Ln = La, Pr, Nd, x = 0.1, 0.2) exhibit enhanced electrocatalytic activity in comparison with their parent compound BaCo0.7Fe0.3O3−δ, with Pr0.1Ba0.9Co0.7Fe0.3O3−δ reaching area specific resistance of 0.038 and 0.026 Ω cm2 and peak power densities of 905.9 and 1236.4 mW cm−2 at 650 and 700 °C, respectively. Such enhancement is a result of the stabilized cubic structure and the promoted oxygen vacancy formation and oxygen adsorption-dissociation process due to rare-earth doping (Pr is more effective for its redox-active character) by the combination of experimental characterization and first-principles calculation. Furthermore, Pr-doped materials also maintain favorable durability at 600 °C (800 mA cm−2 for ~150 h). These findings in this work may provide new insights into the design of cathode materials for other perovskite systems in SOFCs, especially those involving rare earths.

Promotion on electrochemical performance of Ba‐deficient Ba1 − xBi0.05Co0.8Nb0.15O3 − δcathode for intermediate temperature solid oxide fuel cells

Reducing the operating temperature is the developing trend for solid oxide fuel cells. The key is to develop the cathode with high electrocatalytic activity for oxygen reduction reaction operated at reduced temperatures. Ba-deficient Ba1 − xBi0.05Co0.8Nb0.15O3 − δ (Ba1 − xBCN, 0 ≤ x ≤ 0.10) are synthesized by solid-state reaction method and evaluated as novel cathodes for intermediate-temperature solid oxide fuel cells. Ba1 − xBCN is preserved to primitive cubic perovskite phase and meets the compatibility requirement with gadolinium doped ceria oxide (GDC) electrolyte at 950°C. Though the Ba deficiency distorts the cell symmetry, it improves the charge transfer steps rapidly, ascribing to the improvement of oxygen vacancy concentration. The polarization resistance of Ba0.95BCN is as low as 0.056 Ω cm2 in air at 700°C. The peak power density of the single cell with this cathode is as high as 1.41 W cm−2 at 750°C with wet H2 as fuel and air as oxidant, indicating the great potential for enhanced performance of Co-based cathodes with A-site deficiency.

Enhanced electrocatalytic activity and CO2 tolerant Bi0.5Sr0.5Fe1-Ta O3- as cobalt-free cathode for intermediate-temperature solid oxide fuel cells

Abstract One of the significant motivations in developing intermediate-temperature solid oxide fuel cells (IT-SOFCs) is to design cobalt-free cathodes with high electrocatalytic activity and CO 2 tolerance ability. In this work, iron-based perovskite materials Bi 0.5 Sr 0.5 Fe 1- x Ta x O 3- δ are investigated as potential cathodes for IT-SOFCs. The effects of Ta doping on crystal structure, thermal expansion coefficients and electrocatalytic activities are systematically evaluated. Among the Ta-doped oxides, Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ exhibits the highest electrochemical performance with the lowest polarization resistance ( R p ) of 0.124 Ω cm 2 at 700 °C in air. The peak power density of the single cell with Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ cathode reaches 1.36 W cm −2 at 700 °C. Compared to Bi 0.5 Sr 0.5 FeO 3- δ , the improved CO 2 tolerance of Ta-doped oxides can be attributed to the high acidity of Ta 5+ cations and the increased average metal bond energy (ABE) within the material. Further study proves that the adsorption-dissociation process of molecular oxygen is the limiting step for oxygen reduction reaction (ORR) on Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ cathode.

Improved thermal expansion and electrochemical performance of La0.4Sr0.6Co0.9Sb0.1O3-δ-Ce0.8Sm0.2O1.9 composite cathode for IT-SOFCs

La0.4Sr0.6Co0.9Sb0.1O3-δ (LSCSb)-xCe0.8Sm0.2O1.9 (LSCSb-xSDC, x = 0, 20, 30, 40 and 50 wt%) composite materials have been studied systemically as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD result shows an excellent chemical compatibility between LSCSb cathode and SDC/LSGM electrolytes. Although electrical conductivity is reduced with the introduction of SDC content, the electrical conductivities of all the composite cathodes are still above 100 S cm−1 at 300–850 °C. Thermal expansion result shows that the increase in SDC content greatly reduces thermal expansion coefficients (TECs) and the TEC for the LSCSb-50SDC cathode attains as low as 13.1 × 10−6 K−1 at 30–900 °C. Polarization resistance (Rp) decreases monotonously with increasing SDC content, and the LSCSb-50SDC cathode shows the lowest polarization with the Rp of 0.086 Ω cm2 at 700 °C. For a 300 μm thick La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte-supported single cell, the maximum power density (Pmax) of the cell with LSCSb-50SDC cathode achieves 432 mW cm−2 at 700 °C. Moreover, the single cell with the LSCSb-50SDC cathode also shows a good cell stability at operating temperature. Above results indicate that LSCSb-50SDC composite material is a potential cathode for IT-SOFCs.

Performance and optimization of perovskite-type La1·4Ca0·6CoMnO5+δ cathode for intermediate-temperature solid oxide fuel cells

There has been a considerable interest in improving electrocatalytical activity of doped lanthanum manganite and thermal stability of cobaltite cathodes. In the current work, a perovskite-type oxide La1·4Ca0·6CoMnO5+δ (LCCM), as a combination of manganite and cobaltite perovskites, is developed as a potential cathode for intermediate-temperature solid oxide fuel cells. The LCCM has a monoclinic structure and highly structural stability at RT-900 °C. The LCCM exhibits good chemical compatibility and relatively matched thermal expansion coefficient with the La0·9Sr0.1Ga0.8Mg0·2O3–δ (LSGM) and Sm0.2Ce0·8O1.9 (SDC) electrolytes up to 1000 °C. The mixed valence states of Co2+/3+ and Mn3+/4+ coexist in the LCCM. The LCCM exhibits a typical p-type semiconducting behavior, and the sample sintered at 1300 °C possesses the highest conductivity of 223 S cm−1 at 800 °C. The maximum power density of NiO-SDC/SDC/LSGM/LCCM single cell is 445 mW cm−2 at 800 °C. The electrochemical performance, thermal expansion behavior and stability of LCCM are further improved by adding appropriate amounts of SDC. The LCCM-30 wt% SDC composite cathode shows the best electrochemical performance: the area specific resistance is decreased by 68% at 800 °C, and the maximum power density is increased by 22%.

Highly accelerated oxygen reduction reaction kinetics in colloidal-processing-derived nanostructured lanthanum strontium cobalt ferrite/gadolinium-doped ceria composite cathode for intermediate-temperature solid oxide fuel cells

Fully nanostructured La0.6Sr0.4Co0.2Fe0.8O3-δ/Gd0.2Ce0.8O1.9 [lanthanum strontium cobalt ferrite (LSCF)/gadolinium-doped ceria (GDC)] composite cathode is successfully demonstrated with conventional powder processing using nanocomposite particles, grown via a colloidal-processing-based bottom-up approach, as starting material. The cathode/electrolyte interface adheres well at a relatively low temperature of 900 °C because of the promoted surface diffusion of constituent elements by the higher surface energy of the nano-sized particles. By contrast, successful fabrication of a nanostructured porous cathode composed of uniformly distributing LSCF and GDC grains with a diameter of 50–70 nm strongly supports the prevented grain growth and pore closure by the co-existing hetero-phases in the composite particles acting as bulk diffusion barrier of each other's constituents during sintering. The nanocomposite cathode exhibits quite low area-specific polarization resistances for oxygen reduction reaction (ORR) of 0.127, 0.054, 0.032, 0.015 and 0.009 Ω cm2 at 600, 650, 700, 750 and 800 °C, respectively. These are significantly lower than those reported in the literature. The highly accelerated ORR kinetics contribute directly to the very high power densities of the anode-supported cells of 0.40, 0.77, 1.40, 2.32, and 3.29 W cm−2 at 600, 650, 700, 750, and 800 °C, respectively, with a cell voltage at 0.7 V.

YBaCo2O5+δ-based double-perovskite cathodes for intermediate-temperature solid oxide fuel cells with simultaneously improved structural stability and thermal expansion properties

The poor structural stability and high thermal expansion coefficient of YBaCo2O5+δ (YBCO) cathode seriously impede its practical application in intermediate-temperature solid oxide fuel cells (IT-SOFCs). Herein, single- and double-doped YBaCoCuO5+δ (YBCC), YBaCoFeO5+δ (YBCF) and YBaCo2/3Fe2/3Cu2/3O5+δ (YBCFC) are comparatively studied to assess the influences of doping strategy on stability, thermal and chemical compatibilities. The improvement of structural stability and thermal expansion properties of YBCO is achieved simultaneously by the Fe or/and Cu doping in Co-site. First-principles calculations further confirm that the substitution of Fe or/and Cu for Co improve the structural stability compared to undoped YBCO. The YBCC and YBCFC exhibit good thermal and chemical compatibility with La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte below 950 °C. Moreover, the YBCC cathode displays better electrocatalytic activity in the studied cathodes, in which the area specific resistance is 0.138 Ω cm2 at 700 °C. The YBCC cathode shows good electrochemical stability over a 20-h test period. The Cu-doped YBCC double perovskite has stable structure and excellent thermal and chemical compatibility, making it a good cathode candidate for IT-SOFCs. Our findings provide a promising strategy to simultaneously improve structural stability and thermal expansion properties in Co-based perovskites, thus greatly extending their applications.

Nanoporous silver cathode surface-treated by aerosol-assisted chemical vapor deposition of gadolinia-doped ceria for intermediate-temperature solid oxide fuel cells

Herein, a nanoporous silver surface treated with gadolinia-doped ceria (GDC) is evaluated as a cathode for intermediate-temperature solid oxide fuel cells operating below 500 °C. For uniform surface treatment on the porous silver, aerosol-assisted chemical vapor deposition (AACVD) is used; it is a non-vacuum process and is considered as an economical alternative to the expensive vacuum-environment thin-film fabrication methods. Consequently, a uniform coating of AACVD GDC on the Ag surface is successfully achieved, which is confirmed by high-resolution transmission electron microscopy. The optimized amount of AACVD GDC enhances fuel cell performance compared to cells with bare Ag, in terms of the power and long-term stability measured by current–voltage characteristics, electrochemical impedance spectroscopy, and potentiostatic amperometry. This performance is even more significant than that from the cell with a platinum cathode, which, to our best knowledge, is known as the best-performing catalyst for solid oxide fuel cells in the intermediate- and low-temperature regimes. The power enhancement is attributed to the improved kinetics with the GDC surface coating; moreover, this oxide decoration is proven effective in preventing the thermal agglomeration of Ag, as confirmed by the morphology comparison before and after the long-term test.

Synergistic effect study of EuBa0.98Co2O5+δ-Ce0.8Sm0.2O1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

A novel Ba-deficient layered perovskite EuBa0.98Co2O5+δ (EBCO) has been proposed as a high-performance cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Herein we report a systematic study on electrochemical properties of composite materials composed of EBCO and Ce0.8Sm0.2O1.9 (EBCO-xSDC) with x ranging from 0 to 40 wt%. The results indicate that the EBCO-xSDC composite cathodes have excellent electro-catalytic oxygen reduction reaction (ORR) activity thanks to synergistic effects of high electronic conducting EBCO phase and ionic conducting SDC electrolyte. Among all these composite cathodes, EBCO-20SDC exhibits the best cathode performance, as evidenced by a low polarization resistance value of 0.028 Ω cm2 at 700 °C in air. When tested in a complete fuel cell (Ni-YSZ|YSZ|CGO|EBCO-20SDC), a much higher maximum power density of 980 mW cm−2 is achieved, compared with that of EBCO cathode-based fuel cell (505 mW cm−2). Furthermore, the rate-limiting steps toward oxygen reduction reaction at the EBCO-20SDC cathode interface are determined to explore the reaction kinetics and explain the enhanced electrochemical performance.

Sr-substituted SmBa0.75Ca0.25CoFeO5+δ as a cathode for intermediate-temperature solid oxide fuel cells

Layered perovskite oxides have received enormous attention as promising cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this work, the SmBa0.75-xSrxCa0.25CoFeO5+δ (x = 0 and 0.25) samples are synthesized by solid-state reaction method. The effect of Sr doping on the crystal structure, chemical compatibility with the electrolyte, thermal expansion behavior, electrical conductivity, and electrochemical performance have been investigated. The substitution of Sr for Ba improves the electrical conductivity in comparison with the undoped sample. At 800 °C, the area specific resistance (ASR) value is decreased by 24% and the maximum powder density of the anode-supported single cell is increased by 30%. In contrast, at 600 °C, the ASR value is decreased by 41% and the maximum powder density is increased by 102%. The results indicate that the Sr-doping for this system has greater impact on electrochemical performance at lower temperature.

Alkaline metal doped strontium cobalt ferrite perovskites as cathodes for intermediate-temperature solid oxide fuel cells

Perovskite oxides Sr0.9K0.1FexCo1-xO3-δ (SKFCx, x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) are investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) on Sm0.2Ce0.8O1.9 (SDC) electrolyte. The cubic phase of the SKFCx oxides is demonstrated by x-ray diffraction. The SKFCx cathode shows good compatibility with the SDC electrolyte up to 900 °C. Among the investigated compositions, SKFC0.1 displays the highest electrical conductivity of 443–146 S·cm−1 from 350 °C to 800 °C in flow air. The area specific resistances (ASRs) of the SKFCx (x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) cathodes are 0.047, 0.058, 0.066, 0.101, 0.155 and 0.175 Ω cm2 at 650 °C in air on an SDC electrolyte. Among the five tested cathodes, SKFC0.1 exhibits the lowest area specific resistances between 550 °C and 750 °C, when tested on its symmetric cell configuration of cathode|SDC|cathode. The thermally stabilized cubic perovskite structure of the SKFC0.1 powder is demonstrated by high-temperature XRD. The average linear thermal expansion coefficient αL of SKFC0.1 is 18.9×10−6 K−1. A peak power density of 1643 mW·cm−2 is achieved on SKFC0.1|SDC|Ni-SDC anode supported fuel cell at 650 °C. These features, and excellent electrocatalytic activity and good stability, indicate the potential of alkaline metal doped strontium cobalt ferrite perovskites are promising cathode materials for IT-SOFCs.

Structure and electrochemical properties of cobalt-free perovskite cathode materials for intermediate-temperature solid oxide fuel cells

Cobalt-free perovskite oxides, BaFeO3-δ and BaM0.05Fe0.95O3-δ (M = Ti, Zr and Ce), were prepared as the cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). High temperature X-ray diffraction (HT-XRD) results show that BaFeO3-δ and BaTi0.05Fe0.95O3-δ (BTF) have a complex phase composition, and the phase composition changes with temperature. BaZr0.05Fe0.95O3-δ (BZF) has a cubic perovskite structure above 400 °C, while BaCe0.05Fe0.95O3-δ (BCF) has a cubic perovskite structure from room temperature (25 °C) to 1000 °C. Thermogravimetric analysis (TG) and oxygen temperature-programmed desorption (O2-TPD) analysis reveal that the phase transition affects the oxygen-release properties of these materials. In contrast to BaFeO3-δ and BTF showing phase-transition-dependent electrical conductivity, BZF and BCF show typical curves similar to other mixed ionic-electronic perovskite oxides. On an electrolyte of Sm0.2Ce0.8O1.9 (SDC), a single cell with a BCF cathode exhibits polarization resistances of 0.027, 0.046, 0.087 and 0.186 Ω cm2 at 750, 700, 650 and 600 °C, respectively. The peak power densities of the single cell are 482, 415 and 315 mW cm-2 at 750, 700 and 650 °C, respectively. This indicates that the Co-free BCF has a good electrocatalytic activity toward the oxygen reduction reaction and is a promising cathode for IT-SOFCs.

Synthesis and characterization of Ba0.5Sr0.5Co0.8Fe0.1Ni0.1O3-δ cathode for intermediate-temperature solid oxide fuel cells

Perovskite Ba0.5Sr0.5Co0.8Fe0.1Ni0.1O3-δ (BSCFNi) oxide is synthesized and characterized as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The X-ray diffraction (XRD) spectra show that BSCFNi is chemical compatible with La0.9Sr0.1Ga0.83Mg0.17O2.865(LSGM) electrolyte below 950 °C, but weak reaction is observed between BSCFNi cathode and Sm0.2Ce0.8O1.9 (SDC) electrolyte after calcined at 950 °C for 10 h. The XPS results indicate that transition metal cations in BSCFNi sample exist two different valence states, i.e., Co4+/3+, Fe4+/3+ and Ni3+/2+. The average thermal expansion coefficient (TEC) of BSCFNi is 18.7 × 10−6 K−1 between 200 °C and 850 °C in air. The maximum electrical conductivity reaches 35.3 Scm−1 at 425 °C in air. The polarization resistance of BSCFNi cathode on LSGM and SDC electrolytes are 0.033 and 0.066 Ωcm2 at 800 °C, respectively. The maximum power density of LSGM electrolyte-supported single cell with BSCFNi cathode reaches 690 mWcm−2 at 800 °C. These primarily results indicate that BSCFNi is a candidate cathode material for IT-SOFCs.

Preparation and evaluation of novel Bi1.91Sr2Co1.96O7.08 cathode for intermediate temperature-solid oxide fuel cells

Novel cathode material Bi1.91Sr2Co1.96O7.08 (BSCO) was synthesized by ethylene glycol assisted sol-gel method for intermediate temperature solid oxide fuel cells (IT-SOFCs). In addition to its good thermal stability, it shows chemical and thermal compatibility with Ce0.9Gd0.1O2−γ electrolyte. Thermal expansion coefficient of BSCO is found to be approximately 11.2 × 10−6 K−1 from 100 °C to 800 °C, which is the main merit of this material compared with other cobaltite based perovskite cathodes. Electrical conductivity of BSCO is about 8–9 S cm−1 between 600 and 700 °C, and polarization resistance of BSCO cathode on Ce0.9Gd0.1O2−γ electrolyte are 0.1, 0.3 and 1.3 Ω·cm2 at 800, 748 and 695 °C, respectively. Maximum power density based on BSCO/GDC/NiO-GDC cell is 495 mW·cm−2 at 700 oC. Given that the thermal compatibility with the electrolyte and the encouraging electrochemical performance, BSCO could be considered as an alternative cathode material for IT-SOFCs.

La0.6Sr0.4Co0.2Fe0.8O3-δ nanofiber cathode for intermediate-temperature solid oxide fuel cells by water-based sol-gel electrospinning: Synthesis and electrochemical behaviour

Water-based sol-gel electrospinning is employed to manufacture perovskite oxide La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) nanofiber cathodes for intermediate-temperature solid oxide fuel cells. LSCF fibrous scaffolds are synthesized through electrospinning of a sol-gel solution employing water as the only solvent. Morphological characterizations demonstrate that the LSCF fibers have highly crystalline structure with uniform elemental distribution. After heat treatment, the average fiber diameter is 250 nm and the porosity of the nanofiber tissue is 37.5 %. The heat treated LSCF nanofibers are applied directly onto a Ce0.9Gd0.1O1.95 (CGO) electrolyte disk to form a symmetrical cell. Electrochemical characterization is carried out through electrochemical impedance spectroscopy (EIS) in the temperature range 550 °C–950 °C, and reproducibility of the electrochemical performance for a series of cells is demonstrated. At 650 °C, the average measured polarization resistance Rp is 1.0 Ω cm2. Measured performance decay is 1 % during the first 33 h of operation at 750 °C, followed by an additional 0.7 % over the subsequent 70 h.

Crystal structure, thermal expansion and long-term behaviors of SmBaCoO5+δ as cathode for intermediate-temperature solid oxide fuel cells

SmBaCo2O5+δ (SBC) was studied as cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The crystal structure, thermal expansion behavior, and electrochemical performance with long-term operation of SBC were characterized. An orthorhombic layered perovskite structure was observed in SBC cathode by a GSAS program for refinement. The average thermal expansion coefficient (TEC) is 21.6 x 10-6K-1 in the temperature range of 100oC-800oC. For long-term testing, the polarization resistance of SBC cathode increases gradually from 25.77 Ω cm2 for 2 h to 38.77 Ω cm2 for 96 h at 600°C, and an increasing-rate for polarization resistance is around 13,8% h-1. Based on the electrochemical properties, SBC cathode with mixed ionic and electronic conductor (MIEC) behavior is a potential cathode for intermediate temperature solid oxide fuel cells based on a SDC electrolyte.

Highly enhanced electrochemical property by Mg-doping La2Ni1-xMgxO4+δ (x = 0.0, 0.02, 0.05 and 0.10) cathodes for intermediate-temperature solid oxide fuel cells

From the view point of compatibility of both crystalline and element with the prototypical perovskite-type electrolyte of La0.9Sr0.1Ga0.8Mg0.2O3-δ, a series of micro-Mg-doped La2NiO4+δ compounds with compositions of La2Ni1-xMgxO4+δ (x = 0.0, 0.02, 0.05 and 0.10) were successfully synthesized via a traditional sol-gel process and evaluated as cathode for intermediate-temperature solid oxide fuel cells (IT-SOFC). The effects of Mg-doping on crystal structures, bond properties and covalent states were analyzed by X-Ray Diffraction (XRD), Infrared spectra (IR) and X-ray photoelectron spectroscopy (XPS) techniques, respectively. It is found that Mg-doping is benefit for the migration of the interstitial oxygen by weakening the Ni(Mg)O bond. More importantly, we found that Mg doped at the subsurface under the Ni of (001) surface will promote both the O2 adsorption and decomposition process from the analysis of the oxygen migration dynamics. Considering the balance of electronic conductivity, it was indicated that La2Ni0.98Mg0.02O4+δ (LNM0.02) manifested the optimal electrochemical property with the lowest area specific resistance of 0.05 Ω cm2 at 800 °C, and along with a maximum power density of 528 mW cm−2 for an electrolyte supported single cell LNM0.02|LSGM|NiO-SDC at 800 °C with approximately 20% higher than that of the La2NiO4+δ (LN) (∼429 mW cm−2) cathode. The results indicate that introducing micro-dose of Mg into Ni-site in La2NiO4+δ compound is an efficient way to obtain an excellent cathode material for IT-SOFCs.

Structural and electrical properties of Bi3Y0.9W0.1O6.15-La0.8Sr0.2MnO3 (BiYWO-LSM) composites

Electrical conductivity and structural behavior in Bi3Y0.9W0.1O6.15-La0.8Sr0.2MnO3 (BiYWO-LSM) composite cathodes for intermediate temperature solid-oxide fuel cells (IT-SOFCs) have been investigated. The ionically conducting component (BiYWO) was selected as it not only exhibits high oxide ion conductivity at intermediate temperatures, but also shows good long-term stability. The LSM component is a well-known electronic conductor, commonly used for SOFC cathodes and also shows high interfacial polarization effects. Both composite components exhibit similar thermal expansion coefficients. Composites of different molar ratios of components were prepared by sintering the components together at 850°C. Electrical behavior was studied by a.c. impedance spectroscopy and transference number measurements were used to determine the ionic and electronic contributions to total conductivity. Percolation type behavior was observed for total conductivity and the percolation threshold value was determined to be in the bismuth rich region of the compositional range, due to the significant difference in the grain sizes of the two components. Ionic and electronic components of the total conductivity at, above and below the percolation threshold are discussed. Stability measurements on a composition close to the percolation threshold show some degree of conductivity decay on prolonged annealing at 650°C, which is partly recoverable on heating to higher temperatures.