Ba1−xPrxCo1−yFeyO3−δ as cathode materials for low temperature solid oxide fuel cells

Ba_1−xPr_xCo_1−yFe_yO_3−δ (BPCF) perovskite oxides have been synthesized and investigated as cathode materials for low temperature solid oxide fuel cells (LT-SOFCs). Compared with those of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) and Sm_0.5Sr_0.5CoO₃ (SSCo) cathode materials, BPCF has a lower polarization resistance at decreased temperatures. In particular, Ba_0.5Pr_0.5Co_0.8Fe_0.2O_3−δ showed the lowest polarization loss among the different compositions as a cathode material for LT-SOFCs. The area specific resistance (ASR) of Ba_0.5Pr_0.5Co_0.8Fe_0.2O_3−δ as a cathode material is 0.70 and 0.185 Ω cm² at 500 °C and 550 °C, respectively. The maximum power density of the cell BPCF/SDC/Ni-SDC with humidified hydrogen as fuel and air as oxidant reaches 860 mW cm⁻² at 650 °C.     

Electrical conductivity of La1−xCaxFeO3−δ solid solutions

La_1−xCa_xFeO_3−δ solid solutions (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) were investigated. The samples were prepared by the polymerizable complex route and characterized by X-ray diffraction and complex impedance spectroscopy techniques. Results reveal the formation of a single perovskite phase for the La_1−xCa_xFeO_3−δ (0≤x≤0.5) compositions. However, the La_0.4Ca_0.6FeO_3−δ sample is a mixture of many phases: perovskite, calcium ferrite and iron oxide. The unsubstituted lanthanum ferrite oxide, as well as the substituted samples, exhibits an orthorhombic symmetry. The direct current conductivity analyses reveal a typical negative temperature coefficient of the resistance behaviour for all the samples. The incorporation of calcium into the lanthanum ferrite lattice results in a significant improvement of the direct current conductivity. In fact, La_0.8Ca_0.2FeO_3−δ oxide shows the optimal conduction value. For all the studied compositions, a change in the activation energy is highlighted around 440 °C. This behaviour is attributed to the antiferromagnetic to paramagnetic transition of lanthanum ferrite. As for the alternating current conductivity, it obeys the Jonsher's power law. The correlated barrier hopping model is proposed to describe the transport mechanism in the studied matrix.     

Chemical stability and electrochemical properties of CaMoO3−δ for SOFC anode

In an effort to develop alternative anode materials based on mixed conducting ceramics capable of offering high mixed ionic-electronic conductivity, stability to redox cycles, and limited activity for carbon formation to Ni/YSZ cermets, CaMoO₃ ceramics for application as a solid oxide fuel cell (SOFC) anode material were synthesized as a function of temperature and oxygen partial pressure (pO₂). CaMoO₃ perovskite-dominant powders were obtained by reducing the CaMoO₄ showing a structure of orthorhombic unit cells with the following lattice parameters: a = 5.45 Å, b = 5.58 Å, and c = 7.78 Å. The equilibrium total conductivity of CaMoO₃, measured by DC 4-probe method in 5% H₂/balance N₂ condition (pO₂ ≈ 10⁻²² atm) at various temperatures, decreased with increasing temperature below 400 °C, indicating metallic properties with an activation energy of 0.028 eV. Between 400 °C and 600 °C, the equilibrium total conductivity slightly increased, and finally sharply decreased at 800 °C. The Mo metal precipitation during measurement was thermodynamically proved by the predominance diagram for CaMoO₃. Finally, a fuel cell with CaMoO₃ anode exhibited poor performance with a maximum power density of only 14 mW/cm² at 900 °C, suggesting that further research is needed to enhance the ionic conductivity and thus improve the catalytic properties.     

Microstructure of Ba1−xLaxTiO3−δ ceramics sintered by Spark Plasma Sintering

Nano-sized Ba_1−xLa_xTiO₃ (0.00 ≤ x ≤ 0.14) powders were prepared by a coprecipitation method and calcined at 850 °C in air. The corresponding ceramics were obtained by Spark Plasma Sintering (SPS) at 1050 °C. These ceramics are oxygen deficient and are marked as Ba_1−xLa_xTiO_3−δ. Both powders and ceramics were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The effect of lanthanum concentration on the densification behavior, on the structure and the microstructure of the oxides was investigated. Average grain sizes are comprised between 54 (3) nm and 27 (2) nm for powders, and 330 (11) nm and 36 (1) nm for ceramics according to the La-doping level. Powders crystallize in the cubic (or pseudo-cubic) perovskite phase. The structure of ceramics consists in a mixture of cubic (or pseudo-cubic) and tetragonal perovskite type phases. As the lanthanum content increases, the tetragonality of the samples decreases, as well as the grain size.     

Preparation and electrochemical properties of SiO2–non-graphitizable carbon composites as negative electrode materials for Li-ion batteries

SiO₂–non-graphitizable carbon composites were prepared by pyrolysis of a mixture of ethyl cellulose and nano-sized SiO₂. The composite electrode showed high reversibility in insertion and/or extraction reactions of Li ions at potentials below 1 V with little hysteresis after the 2nd cycle, whereas a large irreversible capacity was observed in the 1st cycle. This reversible capacity increased with increasing SiO₂ content above 5 wt%. Li ion transfer at the interface between a composite electrode and an electrolyte was studied by ac impedance spectroscopy. In the Nyquist plots, a semi-circle that was assigned to charge-transfer resistance (R _ct) because of Li ion transfer across the interface between the composite electrode and electrolyte appeared at potentials below 1 V. The values of R _ct decreased with increasing SiO₂ content. These results indicate that both a decrease in R _ct and an increase in reversible capacity can be achieved by use of SiO₂–non-graphitizable carbon composite electrodes; this would lead to Li-ion batteries with higher power and energy density.     

Submicron-sized cube-like α-Fe2O3 agglomerates as an anode material for Li-ion batteries

Submicron-sized cube-like α-Fe₂O₃ agglomerates were successfully fabricated via hydrothermal technique. The material showed a high reversible capacity of 900.2 mAh g⁻¹ and excellent capacity retention of 88.9% after 35 cycles at a current density of 40 mA g⁻¹. The initial columbic efficiencies of the as-prepared powder were 82.65 and 80.57% at current densities of 40 and 80 mA g⁻¹, respectively, which is higher than that of other α-Fe₂O₃ electrodes reported so far. We believe that the small crystal size and the high structure stability are responsible for the drastic improvement in initial coulombic efficiency and reversibility.     

Characterization of NdSrCo1−xFexO4+δ (0 ≤ x ≤ 1.0) intergrowth oxide cathode materials for intermediate temperature solid oxide fuel cells

NdSrCo_1−xFe_xO_4+δ (0 ≤ x ≤ 1.0) intergrowth oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). All the cathodes prepared by a glycine nitrate process (GNP) indicated single phase intergrowth oxides. The introduction of Fe for Co leads to decrease TEC values and electrical conductivity, and increase polarization resistance and oxygen content. The polarization resistance of NdSrCoO_4+δ composition is 0.16 Ω cm² at 800 °C in air atmosphere, which is the best electrochemical performance compared with other compositions.     

Phase equilibria and dielectric properties of Bi3+(5/2)xMg2−xNb3–(3/2)xO14−x cubic pyrochlores

Subsolidus pyrochlores with the proposed formula, Bi_3+(5/2)xMg_2−xNb_3−(3/2)xO_14−x (0.14≤x≤0.22) were successfully synthesised at the firing temperature of 1025 °C using conventional solid-state reaction. The excess Bi³⁺ charge was offset by removal of relative proportion of Mg²⁺ and Nb⁵⁺ together with creation of oxygen non-stoichiometry in order to preserve electroneutrality of the system. These samples were crystallised in cubic structure with space group of Fd3m, No. 227 and their refined lattice parameters were in the range of 10.5706 (3)–10.5797 (7) Å. The surface morphologies of the samples as confirmed by scanning electron microscopy analysis were of irregular shaped grains while their crystallite sizes of ~30–85 nm were calculated using the Scherrer equation and the Williamson–Hall method. No thermal event was discernable indicating these pyrochlores were thermally stable within a studied temperature range of ~30–1000 °C. The recorded dielectric constants of Bi_3+(5/2)xMg_2−xNb_3−(3/2)xO_14−x (0.14≤x≤0.22) subsolidus pyrochlores were generally above ~160 and their dielectric losses were in the order of 10⁻⁴–10⁻³ at the frequency of 1 MHz and temperature of ~30 °C. Meanwhile, these ceramic samples also exhibited negative temperature coefficient of relative permittivity between −528 and −742 ppm/°C in the temperature range of ~30–300 °C.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ cathode prepared by the citrate-EDTA complexing method

This study reports the successful preparation of single-phase perovskite (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ (x = 0-0.2) by the citrate-EDTA complexing method. The crystal structure, thermal gravity analysis, coefficient of thermal expansion, electrical conductivity, and electrochemical performance of (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The lattice parameter a of (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ decreases as the amount of Mn doping increases. The coefficients of thermal expansion of the samples are in the range of 21.6-25.9 × 10⁻⁶ K⁻¹ and show an abnormal expansion at around 400 °C associated with the loss of lattice oxygen. The electrical conductivity of the (Ba_0.5Sr_0.5)_0.8La_0.2Fe_1−xMn_xO_3−δ samples decreases as the amount of Mn-doping increases. The electrical conductivity of the samples reaches a maximum value at around 400 °C and then decreases as the temperature increases. The charge transfer resistance, diffusion resistance and total resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2Fe_0.8Mn_0.15O_3-δ-Ce_0.8Sm_0.2O_1.9 composite cathode electrode at 800 °C are 0.11 Ω cm², 0.24 Ω cm² and 0.35 Ω cm², respectively.     

Synthesis and electrochemical properties of α-LiVOPO4 as cathode material for lithium-ion batteries

Triclinic α-LiVOPO₄ with excellent electrochemical properties is prepared, using δ-VOPO₄, LiNO_3, and a highly conductive carbon material (acetylene black) as raw materials, by a two-step method, for the first time. Transmission electron microscopy reveals that the synthesized nanoscale α-LiVOPO₄ is approximately 50–100?nm in size, and its surface is covered by 1.68?nm thick acetylene black, which not only improves the ionic conductivity of the material, but prevents material-size growth at high temperature, and particle agglomeration. In addition, the initial discharge capacity of α-LiVOPO₄ sintered at 600?°C over 10?h is the highest, reaching 111.7?mAh?g^?1 at 0.05?°C. The capacity retention rate is 95.1%, which is 106.3?mAh?g^?1 after 50 cycles.     

LaBaCuFeO5+δ-Ce0.8Sm0.2O1.9 as composite cathode for solid oxide fuel cells

The performance of the LaBaCuFeO_5+δ-Ce_0.8Sm_0.2O_1.9 (LBCF-SDC) composite cathodes was studied in this paper. Electrical conductivity, thermal expansion and electrochemical properties were investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. The thermal expansion coefficients of the LBCF-SDC were between (16.3 and 13.4) × 10⁻⁶ K⁻¹ from 30 to 850 °C, which was lower value than LBCF (17.0 × 10⁻⁶ K⁻¹). AC Impedance spectroscopy measurements of LBCF-SDC/SDC/LBCF-SDC test cell were carried out. Polarization resistance values for the LBCF-SDC10 cathode was as low as 0.097 Ω cm² at 750 °C.     

Suppression of 3D mobility of carrier and superconductivity by Y substitution in Cu0.5Tl0.5Ba2(Ca2−xYx)Cu3O10−δ samples

Bulk Cu_0.5Tl_0.5Ba₂(Ca_2−xY_x)Cu₃O_10−δ superconductor ceramic samples were synthesized by the conventional solid-state method and characterized by X-ray diffraction, dc-resistivity, ac-susceptibility and Fourier Transform Infrared spectroscopy. The main purpose of this study was to investigate the role of charge carriers and the effect of Y substitution at Ca sites in between the CuO₂ planes on superconductivity. The superconducting properties are suppressed by Y substitution at Ca sites in between the CuO₂ planes of Cu_0.5Tl_0.5Ba₂(Ca_2−xY_x)Cu₃O_10−δ samples. It is most likely that Y³⁺ may create correlated domains in between the CuO₂ planes and localizes the carriers, which lowers the diamagnetic screening and suppresses the superconductivity. Therefore, cationic substitution reduces the three dimensional (3D) mobility of carriers, resulting in the reduction of the Fermi vector and velocity of the carriers, which in turn suppresses the superconducting properties of the material.     

Ionic transport properties and their variations with grain size in nanostructured double doped cerias such as Ce0.8Gd0.1Pr0.1O2−δ and Ce0.8Gd0.15Pr0.05O2−δ

This work presents the ionic transport properties in some nanocrystalline double doped cerias, i.e., Ce_0.8Gd_0.1Pr_0.1O_2−δ and Ce_0.8Gd_0.15Pr_0.05O_2−δ with various average grain sizes, in the intermediate temperature region. The correlations between electrical and dielectric properties of these materials have been established and variation of conductivity with respect to temperature has been thoroughly discussed. All the materials are found to be ionic in nature and show high value of ionic conductivity at intermediate temperatures. The nanocrystalline Ce_0.8Gd_0.1Pr_0.1O_2−δ material (irrespective of grain size), shows lowest association energy, i.e., 0.03 eV, which is close to the theoretically predicted lowest value (0.02 eV) in double doped ceria. A repulsive force is expected between the free oxygen vacancies at the grain boundary regions at higher temperatures, which restricts the rise in grain boundary conductivity and results in decrease in total conductivity.     

微波水热法合成Li4Ti5O12及其性能

采用微波水热法和水热法制备锂离子电池负极材料Li4Ti5O12,比较了合成方法对Li4Ti5O12电化学性能的影响,考察了其结构和形貌及电化学性能.结果表明,两种方法均合成了尖晶石结构的Li4Ti5O12,微波水热法合成的样品电化学性能较好,颗粒尺寸为200~300 nm,分布均匀,比表面积较大,在1 C的放电条件下,首次放电比容量为151.33 mA·h/g,97次循环后放电比容量为140.94 mA·h/g,保持率为93.14%,且电化学阻抗较小.     

Microstructural adjustment of Ni–BaCe0.9Y0.1O3−δ cermet membrane for improved hydrogen permeation

Dense ceramic membranes are usually hybridized with an electronically conductive metallic phase to enhance their hydrogen permeation fluxes, thereby increasing the hydrogen-production efficiency of hydrogen separation membranes. Herein, the hydrogen-separation properties of membranes fabricated from cermets containing BaCe_0.9Y_0.1O_3−δ (BCY) as the proton-conducting ceramic phase and Ni as the electronic-conducting metal phase were investigated with respect to the compositions of the Ni–BCY mixture. Because the hydrogen permeability of a cermet membrane is seriously affected by microstructural parameters such as grain size and homogeneity of the cermet mixture used to fabricate it, we tried to optimize the microstructures and compositions of the Ni–BCY cermets by controlling their fabrication conditions. A high-energy milling process was employed to fabricate fine-grained, dense membranes that exhibited high levels of mixing homogeneity. From the adjustment of composition and microstructure of Ni–BCY composites, the hydrogen permeability of Ni–BCY cermet membranes can be significantly increased so that hydrogen fluxes of ~0.76 cm³/(min cm²) at 800 °C can be achieved.     

La0.8Sr0.2Co0.3Fe0.7O3−δ as a novel candidate coating material for the positive current collector in sodium sulfur battery

The corrosion behaviors of perovskite La_0.8Sr_0.2Co_0.3Fe_0.7O_3−δ (LSCF) in the sodium tetrasulfide melt have been studied to demonstrate its possibility to be used as a coating material for the positive current collector in the sodium sulfur battery (Na/S). The electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are applied in the study. The results demonstrate that the corrosion process of the LSCF in sodium tetrasulfide melt is activation controlled. The corrosion current density of the LSCF is approximate 10 times smaller than that of the 316L stainless steel. Two compact corrosion layers which may act as a stable barrier retarding the corrosion process have formed on the surface of LSCF after immersed for 130 days. The promising results suggest that LSCF exhibits high corrosion resistance against molten sodium tetrasulfide and may be an appropriate candidate coating material for the positive current collector in Na/S battery.     

尖晶石型Li4Ti5O12负极材料的研究进展

锂离子电池以其高功率和高能量密度等优点而被认为是电动汽车和其他便携式电器的最有前途的动力能源。提高电化学性能及其安全性是锂离子电池面临的主要挑战。尖晶石型钛酸锂因具有良好的结构稳定性、安全性以及高倍率充放电性能,成为锂离子动力电池负极材料的研究热点。综述了国内外钛酸锂负极材料的最新研究进展,包括：合成方法,掺杂、表面改性,重点阐述了碳材料表面改性及其应用,展望了钛酸锂作为混合动力电池负极材料的发展趋势。     

Surface layer formation on Li1 + xMn2O4 − δ thin film electrodes during electrochemical cycling

A surface layer formation on positive Li_{1 + x}Mn₂O_{4 − δ} thin film model electrodes as a result of electrochemical cycling procedures has been detected and characterized by scanning electron microscopy and X-ray photoemission spectroscopy. These thin film spinel electrodes, prepared by pulsed laser deposition, were cycled in 1 M LiClO₄ in propylene carbonate between 3.5 and 4.4 V vs. Li/Li⁺ at 40 °C and stopped at defined potentials and cycle numbers. The observed surface layers show, depending on the cycling conditions, a spotty and/or layered appearance and the fraction of this layer covering the cycled electrode depends on the charge potential and the number of electrochemical cycles.     

Electrochemical properties of Sr1−xCexMnO3 (0.1≤x≤0.4) – GDC composite cathodes for IT-SOFCs

The electrochemical properties of Sr_1−xCe_xMnO₃ (SCM, 0.1≤x≤0.4)–Gd_0.2Ce_0.8O_2−x (GDC) composite cathodes were determined by impedance spectroscopy. The study focused on the doping effect of Ce in the composite cathodes. Single-phase perovskite was obtained for 0.1≤x≤0.3 in SCM. No reaction occurred between the Sr_0.7Ce_0.3MnO₃ electrode and the GDC electrolyte at an operating temperature of 800 °C for 100 h. In the single phase perovskite region, lattice expansion occurred due to the reduction of Mn⁴⁺ to Mn³⁺ at B-sites, and this was attributed to an increase in Ce content. Ce doping enhanced the electrode performance of SCM–GDC composite cathodes, and best electrode performance was achieved for the Sr_0.7Ce_0.3MnO₃–GDC composite cathode (0.93 Ω cm² and 0.47 Ω cm² at 750 °C and 800 °C, respectively). The improvement in electrode performance was attributed to increases in charge carriers induced by a shift of some Mn from +4 to +3 and to the formation of surface oxygen vacancies caused by Mn⁴⁺ to Mn³⁺ conversion at high temperatures.