Electrochemical performances of Ag–(Bi2O3)0.75(Y2O3)0.25 composite cathodes

The electrochemical performances of Ag–Y_0.25Bi_0.75O_1.5 (YSB) composite cathodes on Ce_0.8Sm_0.2O_1.9 (SDC) electrolytes have been investigated at intermediate temperature using AC impedance spectroscopy. The results indicated that the electrochemical performances of these composites are quite sensitive to the compositions and the microstructures of the cathode. The optimum YSB addition to Ag resulted in 10 times lower area specific resistance. The ASR of Ag-50 vol.% YSB was about 0.12 Ωcm² at 700 °C as compared to 3.9 Ωcm² for Ag cathodes. The observed high performance of Ag–YSB composite cathodes might be due to the high oxygen-ion conductivity of YSB and its high catalytic activity for oxygen reduction.     

Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries

In this paper we report a novel Mn₃O₄ electrode doped with nano-NaBiO₃. It is demonstrated that doping with nano-NaBiO₃ alters the electrochemical inertia of Mn₃O₄, converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn₃O₄ electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn₃O₄ electrode doped with nano-NaBiO₃ can reach and become stable at 372 mAh g⁻¹ under 60 mA g⁻¹. The doped cathode can also maintain a cycling capacity of 261 mAh g⁻¹ while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g⁻¹. Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn₃O₄ cathode could possibly shorten to as little as 30 min.     

Fabrication and properties of Ba(Zr1−xCex)0.9Y0.1O2.95/NaCl composite electrolyte materials

Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95/NaCl (x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10⁻² S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen.     

Y2O3-BaO-SiO2-B2O3-Al2O3 glass sealant for solid oxide fuel cells

A glass based on Y₂O₃-BaO-SiO₂-B₂O₃-Al₂O₃ (named YBA) has been investigated as sealant for planar solid oxide fuel cells (SOFCs). The YBA glass has been systematically characterized by differential thermal analysis, dilatometer, scanning electron microscopy, impedance analysis, and open circuit voltage to examine their suitability as sealant. The coefficient of thermal expansion of YBA is 11.64 × 10⁻⁶ K⁻¹ between 323 and 873 K. The resistivity is 9.1 × 10⁴ Ω cm at 800 °C. The glass sealant is found to be well adhered with other cell components, such as electrolytes and stainless steels, at an optimum sealing temperature of 800 °C. All measured results showed that the YBA glass appears to be a promising sealant for SOFCs.     

Effect of partial substitution of Co with Fe on the properties of LaNi3.55Mn0.4Al0.3Co0.75−xFex (x=0, 0.15, 0.55) alloys electrodes

The effect of iron substitution on the electrochemical behaviour of LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x compounds (x=0, 0.15, 0.55) has been studied by chronopotentiometry and cyclic voltammetry techniques. The maximum capacity decreases linearly from 308 to 239 mAhg⁻¹ when the iron content increases from 0 to 7.3 wt.% (x=0.55). This decrease can be explained by the corrosion of the alloy in the aqueous KOH electrolyte. In spite of this decrease and of the long time needed for the activation, a good stability of discharge capacity was observed in LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x compounds. The reversibility of the electrochemical redox reaction of LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x alloy electrodes has been observed in the alloys least rich in iron. The hydrogen diffusivity in LaNi_3.55Mn_0.4Al_0.3Co_0.75−xFe_x alloy electrodes decreases when increasing the iron content. The obtained values of the hydrogen diffusion coefficient D_H, varies between 2.1×10⁻⁷ and 8.2×10⁻⁹ cm² s⁻¹ depending on the iron content of the electrode.     

Influence of the ratio between Ni and BaCe0.9Y0.1O3−δ on microstructural and electrical properties of proton conducting Ni-BaCe0.9Y0.1O3−δ anodes

Cermet anode substrates Ni-BaCe_0.9Y_0.1O_3−δ (Ni-BCY10) with varied ratios between Ni and BCY10 were prepared. BCY10 powders were prepared by the citrate-nitrate auto-combustion method and anode substrates were prepared by the method of evaporation and decomposition of solutions and suspensions. Sintered anode substrates were reduced and their properties were examined before and after reduction as a function of the ratio between Ni and BCY10. Microstructural properties of the pellets were investigated using X-ray diffraction analysis and field emission scanning electron microscopy. The influence of the Ni:BCY10 ratio on the microstructure of conducting paths through ceramic and metal parts was discussed. Impedance spectroscopy measurements were used for evaluation of electrical properties of the anode pellets. The high conductivity values of reduced anodes confirmed percolation through Ni particles even for an anode with a reduced amount of nickel. Fuel cell tests were carried out in order to examine the influence of the Ni:BCY10 ratio on fuel cell performance and to compare characteristics of cermet anodes with platinum electrodes. The ratio between Ni and BCY10 did have a slight influence on the power output of fuel cells. Fuel cells with a cermet anode demonstrated a higher power output compared to fuel cells with a platinum electrode.     

Improvement of the electrochemical performance of LiMn2O4 cathode active material by lithium borosilicate (LBS) surface coating for lithium-ion batteries

The LBS coating on the surface of spinel LiMn₂O₄ powder was carried out using the solid-state method, followed by heating at 425 °C for 5 h in air. The powder X-ray diffraction pattern of the LBS-coated spinel LiMn₂O₄ showed that the LBS coating medium was not incorporated in the spinel bulk structure. The SEM result showed that the LBS coating particles were homogeneously distributed on the surface of the LiMn₂O₄ powder particles. The effect of the lithium borosilicate (LBS) coating on the charge-discharge cycling performance of spinel powder (LiMn₂O₄) was studied in the range of 3.5-4.5 V at 1C. The electrochemical results showed that LBS-coated spinel exhibited a more stable cycle performance than bare spinel. The capacity retention of LBS-coated spinel was more than 93.3% after 70 cycles at room temperature, which was maintained at 71.6% after 70 cycles at 55 °C. The improvement of electrochemical performance may be attributed to suppression of Mn²⁺ dissolution into the electrolyte via the LBS glass layer.     

Sm0.5Sr0.5CoO3 cathode material from glycine-nitrate process: Formation, characterization, and application in LaGaO3-based solid oxide fuel cells

Cathode material Sm_0.5Sr_0.5CoO₃ (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm_0.5Sr_0.5CoO₃ were investigated. The single cell performance was also tested using La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm₂O₄ phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10⁻⁶ K⁻¹ from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm² at 800 and 850 °C, respectively.     

Dielectric relaxation and ionic conductivity studies of [N(CH3)4]2Cu0.5Zn0.5Cl4

WO₃-doped zinc titanate ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. The effects of WO₃ additions on the phase structure and phase transitions of zinc titanate ceramics were investigated by high-temperature X-ray diffractometry (HTXRD) and transmission electron microscopy (TEM). The results showed that the major phase of zinc titanate ceramics transformed from zinc orthotitanate phase to zinc metatitanate phase with the amounts of WO₃ additions increasing. Small WO₃ (<1.00 mass%) addition accelerated the transition of ZnTiO₃ to Zn₂TiO₄, while excessive WO₃ addition restrained the transition. HTXRD showed that WO₃ enhanced the stability of Zn₂Ti₃O₈ and weakened the stability of ZnTiO₃. A precipitate within the Zn₂TiO₄ matrix was observed. Viewed along the orientation of Zn₂TiO₄, the precipitate was found to have a rectangular shape and to be nanometer level in size; its composition was concluded to be Zn₂Ti₃O₈. The dielectric properties of WO₃-doped zinc titanate ceramics were measured at different frequencies. The results showed the decreasing tendency with the increasing measuring frequencies for both the dielectric constants and the loss tangents, and there existed maximum values when the amount of WO₃ was 0.50 mass%.     

Preparation and thermal conductivities of Gd2Ce2O7 and (Gd0.9Ca0.1)2Ce2O6.9 ceramics for thermal barrier coatings

Two kinds of rare earth cerium oxides Gd₂Ce₂O₇ and (Gd_0.9Ca_0.1)₂Ce₂O_6.9 were prepared by solid state reaction method at 1600 °C for 10 h. The phase compositions, microstructures, and their thermal conductivities of these materials were investigated. XRD results revealed that single phase Gd₂Ce₂O₇ and (Gd_0.9Ca_0.1)₂Ce₂O_6.9 with fluorite structure were synthesized. Results of SEM and EDS showed that the microstructures of these materials were dense and no other phases existed among grains. Because of phonon scattering resulted by the oxygen vacancies and difference in atomic mass between substitutional atoms and host atoms, thermal conductivities of Gd₂Ce₂O₇ and (Gd_0.9Ca_0.1)₂Ce₂O_6.9 are lower than that of 8YSZ at 800 °C, and thermal conductivity of (Gd_0.9Ca_0.1)₂Ce₂O_6.9 is lower than that of Gd₂Ce₂O₇. These results imply the Gd₂Ce₂O₇ and (Gd_0.9Ca_0.1)₂Ce₂O_6.9 can be used as novel candidate materials for thermal barrier coatings in the future.     

Effect of Ln2O3 (Ln = La, Pr, Eu, Gd) addition on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics

(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ ceramics added with 0.2 wt.% Ln₂O₃ (Ln = La, Pr, Eu, Gd) were prepared by a citrate method, and the structure and electrical properties of the ceramics were investigated with respect to the size of the lanthanide. All the specimens maintain a coexistence of rhombohedral and tetragonal phases in crystal structure, while no remarkable evolution in microstructure with the lanthanide addition was observed. Compared with (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃, the lanthanide addition resulted in an increased diffuseness in phase transition and a decrease in depolarization temperature (T_d). The variation in dielectric, piezoelectric and ferroelectric properties with the lanthanide addition presents an evident lanthanide size dependence. The addition of La₂O₃ or Pr₂O₃ tailored the electrical properties basically following a soft doping effect, with the specimens added with La₂O₃ and Pr₂O₃ attaining high piezoelectric constants (d₃₃) of 188 and 184 pC/N, respectively. By contrast, the Eu₂O₃ or Gd₂O₃ addition led to an abnormal change in the electrical properties, which was qualitatively interpreted by an internal stress effect.     

Kinetic study on Li2.8(V0.9Ge0.1)2(PO4)3 by EIS measurement

Kinetics for lithium ion transfers in the fast ionic conductor Li_2.8(V_0.9Ge_0.1)₂(PO₄)₃ prepared by solid-state reaction method has been studied by electrochemical impedance spectroscopy (EIS) at various temperatures and the results were correlated with observed cathodic behavior. The specific conductivities of Li_x(V_0.9Ge_0.1)₂(PO₄)₃ (x = 0.9–2.8) versus temperatures were analyzed from blocking-electrodes by Wagner's polarization method and the activation energy was calculated. It was observed that electronic conductivities of Li_x(V_0.9Ge_0.1)₂(PO₄)₃ increased with lithium contents in the materials. The compounds show a reversible capacity of 131 mAh g⁻¹ at low current density (13 mA g⁻¹). Modeling the EIS data with equivalent circuit approach enabled the determination of charge transfer and surface film resistances. The Li ion diffusion coefficient (D_Li⁺) versus voltage plot shows three valleys during the first charge cycle coinciding with the irreversible plateau of the voltage versus lithium content profiles reflecting the irreversible phase change in the compound. The obtained D_Li⁺ from EIS varies within 10⁻⁸ to 10⁻⁷ cm² s⁻¹, so Li_2.8(V_0.9Ge_0.1)₂(PO₄)₃ shows excellent chemical diffusion performance.     

Dielectric and magnetic properties of 0.7Bi(Fe1−xCrx)O3–0.1BaTiO3–0.2PbTiO3 solid solutions

0.7Bi(Fe_1−xCr_x)O₃–0.1BaTiO₃–0.2PbTiO₃ (x = 0, 0.1, 0.2, 0.3) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results revealed that the samples with x = 0–0.3 showed pure perovskite structure. Frequency and temperature dependences of dielectric constants and dielectric loss of the samples were investigated. Both dielectric constant and the loss tangent increased at given frequencies (100 Hz–1 MHz), while the Curie temperature of the solid solutions decreased with increasing Cr content. Room temperature magnetic hysteresis loops indicated that an appropriate amount of Cr could improve magnetization of the solid solutions.     

The characteristics of Li(CoxNi1 − x)O2 cathode powders formed from the fine-sized Co3O4/NiO precursor powders

Li(Co_xNi_1 − x)O₂ (0 ≤ x ≤ 1) cathode powders were prepared by solid state reaction method using Co₃O₄/NiO precursor powders obtained by spray pyrolysis. The effect of the ratios of cobalt and nickel components on the characteristics of Co₃O₄/NiO precursor and Li(Co_xNi_1 − x)O₂ cathode powders were investigated. The Co₃O₄/NiO precursor powders with the ratios of cobalt and nickel components as 1/0, 0.75/0.25 and 0.5/0.5 had submicron size and regular morphologies. On the other hand, the Co₃O₄/NiO powders with the high contents of nickel component had aggregated morphologies of submicron size primary powders. The fine-sized precursor powders formed the fine-sized LiCoO₂ and Li(Co_0.75Ni_0.25)O₂ cathode powders by solid state reaction with LiOH powders. However, the high contents of the nickel component of the Co₃O₄/NiO precursor powders formed the Li(Co_xNi_1 − x)O₂ (0 ≤ x ≤ 0.5) cathode powders with aggregated morphologies and large sizes. The discharge capacities of the powders increased with increasing the nickel content into the Li(Co_xNi_1 − x)O₂ cathode powders up to 188 mAh/g.     

Nanocrystalline LaNi4−xMn0.75Al0.25Cox electrode materials prepared by mechanical alloying (0≤x≤1.0)

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH_x) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi_4−xMn_0.75Al_0.25Co_x (x=0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu₅-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH_x battery. Cobalt substituting nickel in LaNi₄Mn_0.75Al_0.25 greatly improved the discharge capacity and cycle life of the LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacities up to 258 mA h g⁻¹ (at 40 mA g⁻¹ discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi₅-type alloy powders for electrochemical energy storage.     

Dense La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for IT-SOFC's: Sintering study and electrochemical characterization

This paper presents the sintering behaviour of a La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by calcination at 1200 °C during 1 h. This synthesis method gives great uniformity of the powder and allows shaping into compacts without requiring a grinding step. The grain size distribution (between 0.5 and 4 μm) favours a good sintering behaviour: open porosity disappear at 1400 °C and relative densities over 99% can be achieved after 6 h at 1450 °C. The same powder can also be sintered into a thin disc of ∼100 μm thickness. The characterization of the dense material by impedance spectroscopy shows that the activation energies below and above 600 °C are 1.0 eV and 0.7 eV, respectively. The conductivity at 800 °C is ∼0.11 S cm⁻¹. Special attention is devoted to the temperature range between 200 °C and 400 °C, where the intragrain and intergrain contributions can be distinguished. The analysis of the parameters describing the intragrain constant phase element in the equivalent circuit suggests that, above 325 °C, the system evolves from a distribution of relaxation time to only one relaxation time. The analysis of the data by the complexes permittivity show that ionic oxide conduction mechanism would occur in two steps. In the first, an oxygen vacancy would be released and, in the second, the migration of the ionic oxide would take place in the material.     

B参杂对NiO/Ni(OH)2电极材料电容性能的影响

通过化学镀再电化学氧化的方法在铜片表面制备出带有微米微坑和微米微球的均一NiO/Ni(OH)₂和B参杂的NiO/Ni(OH)₂(B)两种电极材料,采用扫描电镜(SEM/EDX)、X射线衍射(XRD)、X射线光电子能谱(XPS)和电化学技术对所制备的两种电极材料进行表征和电化学性能测试。SEM、XRD和XPS的测试结果表明, 所制备的两种电极材料由Ni、NiO和Ni(OH)₂组成,并且NiO/Ni(OH)₂(B)中B的参杂量可达14.6wt%。循环伏安测量和恒电流充放电试验表明,两种电极材料均具有较高的电化学活性和可逆性;在1 A/g的充放电电流密度下, 两种NiO/Ni(OH)₂和NiO/Ni(OH)₂(B)电极材料经历10000次充放电循环后分别给出了1380 和1930F/g的比电容, 显示出较高的比电容特性和良好的电化学稳定性;电化学阻抗谱表明NiO/Ni(OH)₂(B)电极材料较NiO/Ni(OH)₂电化学反应电阻降低了约2个数量级;Ragone曲线揭示了所制备的两种电极材料具有较高的功率密度和较低的能量密度。B的参杂使得NiO/Ni(OH)₂(B)电极材料表面氧化物含量增大并且形成微米微球形貌,增大了电极表面积以及与电解液的接触和润湿作用,降低了电极材料表面能带带隙能,从而导致较小的电化学反应电阻和电导率的提高是其显示优异赝电容性能的主要原因。     

SmBaCoCuO5+x as cathode material based on GDC electrolyte for intermediate-temperature solid oxide fuel cells

The performance of SmBaCoCuO_5+x (SBCCO) cathode has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion and electrochemical performance on Ce_0.9Gd_0.1O_1.95 (GDC) electrolyte are evaluated. XRD results show that there is no chemical reaction between SBCCO cathode and GDC electrolyte when the temperature is below 950 °C. The thermal expansion coefficient (TEC) value of SBCCO is 15.53 × 10⁻⁶ K⁻¹, which is ∼23% lower than the TEC of the SmBaCo₂O_5+x (SBCO) sample. The electrochemical impedance spectra reveals that SBCCO symmetrical half-cells by sintering at 950 °C has the best electrochemical performance and the area specific resistance (ASR) of SBCCO cathode is as low as 0.086 Ω cm² at 800 °C. An electrolyte-supported fuel cell generates good performance with the maximum power density of 517 mW cm⁻² at 800 °C in H₂. Preliminary results indicate that SBCCO is promising as a cathode for IT-SOFCs.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Low field magnetoresistance properties of (La0.75Sr0.25)1.05Mn0.95O3 polycrystalline thin films on a-SiO2/Si substrates prepared by ex-situ solid phase crystallization

We report the low field magnetoresistance (LFMR) properties of (La_0.75Sr_0.25)_1.05Mn_0.95O₃(LSMO) films on a-SiO₂/Si substrates, prepared by ex-situ solid phase crystallization of amorphous films deposited by dc-magnetron sputtering at room temperature. The average grain size of the LSMO films was gradually increased with increasing annealing temperature (T _an ) and film thickness. High T _an also caused the growth of an amorphous inter-diffusion layer between a-SiO₂ and LSMO. The highest LFMR values of 16 and 1.0 % were achieved at 100 K, 1.2 kOe and 300 K, 0.5 kOe, respectively, from an LSMO film of 200 nm thickness annealed at 900 °C. In accordance with a modified brick layer model, grain boundary areal resistance gradually increased with increasing T _an and decreasing film thickness due to the penetration of the amorphous inter-diffused phase into the LSMO grain boundary. Improved LFMR values are attributable to modification of the LSMO grain boundary into a more effective spin-dependent scattering center.