Investigation of chemisorbed oxygen, surface segregation and effect of post-treatments on La0.8Sr0.2MnO3 powder and screen-printed layers for solid oxide fuel cell cathodes

In order to better understand the mechanism of the reaction of oxygen reduction at the surface of strontium doped lanthanum manganites (LSM) cathodes in solid electrolyte fuel cells (SOFC), the surface properties of La_0.8Sr_0.2MnO₃ powders and screen-printed layers have been characterised by various techniques.Strontium enrichment at the surface has been evidenced by X-ray photoelectron spectroscopy according to the conditions of annealing (temperature, oxygen pressure) and polarisation treatments of the samples.The interaction between oxygen and La_0.8Sr_0.2MnO₃ for SOFC cathodes has been studied by thermo-programmed desorption, in situ infrared spectrometry and calorimetry. The results indicate that various adsorbed oxygen species may exist on the surface of LSM depending on temperature.The presence of various adsorbed oxygen species and the surface Sr segregation are important factors to consider in the mechanism of oxygen reduction at LSM SOFC cathodes since they could be responsible for many discrepancies between the interpretations that can be found in the literature data.     

Spray pyrolytic deposition of transparent aluminum oxide (Al2O3) films

Optically transparent Al₂O₃ films has been synthesized, on quartz substrates at 500, 600 and 700 °C, from 0.02 M aluminum acetyl acetonate (Al(acac)₃) in ethanol, by using ultrasonic spray pyrolysis technique. The films synthesized at 500, 600 and 700 °C are amorphous having average particle sizes 27 ± 6, 18 ± 3 and 14 ± 3, respectively. The films are found to be 95% optically transparent in the visible region. The optical transparency of the films in the ultraviolet region is found to increase with increase in deposition temperature. The observed increase in optical band gap and decrease in refractive index is attributed to the decrease in particle size with increase in deposition temperature. The stoichiometry and chemical bonding of the amorphous film studied using XPS and FTIR spectroscopy revealed the presence chemisorbed oxygen.     

Ce0.8Sm0.2O1.9 synthesis for solid oxide fuel cell electrolyte by ultrasound assisted co-precipitation method

In this study, the synthesis of Ce_0.8Sm_0.2O_1.9 (SDC) solid electrolyte by the ultrasound assisted co-precipitation method was accomplished to explore the effects of ultrasound power, ultrasound pulse ratio and probe type upon the ionic conductivity of SDC as well as the lattice parameter, the microstructure and the density. Fine powders of uniform crystallite sizes (average 11.70 ± 0.62 nm) were obtained, needing lower sintering temperature. The SDC powders were successfully sintered to a relative density of over 95% at 1200 °C (5 °C min^?1) for 6 h. The micrograph of SDC pellets showed non-agglomerated and well-developed grains with average size of about 200 nm. X-ray diffraction analysis showed that the lattice parameter increased with increasing acoustic intensity and reached a maximum for the 14.94 W cm^?2. Further, a linear relationship was detected between the lattice parameter and the ionic conductivity, inspiring a dopant like effect of US on the electrolyte properties. The highest ionic conductivity as σ_800°C = 3.07 × 10^?2 S cm^?1 with an activation energy E_a = 0.871 kJ mol^?1 was obtained with pulsed ultrasound for an acoustic intensity of 14.94 W cm^?2, using 19 mm probe and 8:2 pulse ratio.     

Spray pyrolytic deposition of solid electrolyte Bi2V0.9Cu0.1O5.35 films

Copper substituted bismuth vanadate films have been successfully deposited first time by spray pyrolysis technique on glass substrates suitable for low temperature solid oxide fuel cells. Desired phase formation of polycrystalline Bi₂V_0.9Cu_0.1O_5.35 (BICUVOX.10) was confirmed by X-ray diffraction technique. These films were further studied with EDAX and SEM techniques for their compositional and morphological characterization. Electrical conductivity of BICUVOX.10 is found to be 5.7 × 10⁻² (Ω cm)⁻¹ at 698 K, predicts the onset temperature for ionic contribution suitable for low temperature SOFC applications. Room temperature complex impedance plot reveals that electrical process arises due to contribution from the grain interior.     

Synthesis and characterization of Gd0.1Ce0.9O1.95 thin films by spray pyrolysis technique

The Gd doped ceria (CGO) in thin layers is of great interest for low temperature operation. In the present investigation, we report on the use of spray pyrolysis technique for the synthesis of CGO thin films. The process parameters were optimized for synthesizing Gd_0.1Ce_0.9O_1.95 films. Films were characterized by XRD, EDS, SEM, and AFM and are observed to be phase pure and dense with surface roughness of the order of ∼5 nm. The d.c. conductivity was also measured and is observed to be ∼0.5 S/cm at 623 K.     

Preparation and characterization of co-doped (Ce0.80La0.15Al0.05O1.90) and multiple-doped (Ce0.80Sm0.10Gd0.05Al0.05O1.90 and Ce0.80Gd0.10Sm0.05Al0.05O1.90) ceria

Attempts have been made to synthesize a few compositions Ce_0.80La_0.15Al_0.05O_1.90, Ce_0.80Sm_0.10Gd_0.05Al_0.05O_1.90, and Ce_0.80Gd_0.10Sm_0.05Al_0.05O_1.90 by citrate–nitrate auto-combustion method. The aim of the present investigation was to study the effect of co-doping and multiple doping on the ionic conductivity of CeO₂ for its use as solid electrolyte in intermediate temperature solid oxide fuel cells. XRD patterns showed that all the samples have fluorite-type crystal structure similar to undoped ceria. Microstructures of thermally etched samples have been studied by scanning electron microscopy. Contributions of grains σ _g and grain boundaries σ _gb to the total conductivity σ _T, have been determined using impedance analysis. Impedance measurements were made in the frequency range 1 Hz–1 MHz and temperature range 250–500 °C. Our experimental results show that multiple doping is more effective than co-doping for improving the oxide ion conductivity of ceria in the materials investigated in the present study.     

Influence of colloidal templates on the impedance spectroscopic behaviour of Pr0.7Sr0.3Fe0.8Ni0.2O3 for solid oxide fuel cell applications

The creation of porous materials with three-dimensional periodicity has been identified as being of potential interest for increasing the overall performance of solid oxide fuel cells (SOFC). In this work, we have investigated the formation of pore systems in the nanometer scale by replicating colloidal templates. Templating methods have been used to prepare iron-nickel-based perovskite Pr_0.7Sr_0.3Fe_0.8Ni_0.2O₃ material with nanoporous microstructure. Polymethyl methacrylate (PMMA), polystyrene (PS) and polycarboxylate (PC) microspheres with different diameters were used as pore formers. These samples were synthesized and characterized by thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction, transmission electron microscopy and field emission scanning electron microscopy. The polarization resistance of the materials was studied by Electrochemical Impedance Spectroscopy. The study demonstrated that templated porosity is maintained and highly influences on the impedance spectroscopic behaviour, being the material synthesized with policarboxylate microspheres the most interesting of the three used templates for SOFC applications.     

Auto-combustion synthesis and properties of Ce0.85Gd0.15O1.925 for intermediate temperature solid oxide fuel cells electrolyte

A typical composition of the system Ce_1 − xGd_xO_2 − δ with x = 0.15 (CGO15) has been synthesized by auto-combustion method. DTA/TGA of the precursor compound indicated the completion of reaction at about 270 °C. Greater than 95% of the theoretical density has been achieved by sintering at 1300 °C for 10 h. Single phase formation in as-burnt stage has been confirmed by its powder X-ray diffraction (XRD) pattern. The structural morphology was studied employing bright field transmission electron micrograph (BFTEM) and high resolution transmission electron micrograph (HRTEM). BFTEM image indicates that particles are highly agglomerated and appear to be dispersed in amorphous matrix. Also BFTEM image reveals that the average particle size is 26 ± 5 nm. The presence of amorphous phase in as-prepared ash was also confirmed by HRTEM and selected area diffraction (SAD). The scanning electron micrograph (SEM) of the thermally etched system shows grains having an average size of 400 nm. Impedance measurements have been made in the frequency range 1 Hz to 1.3 MHz between 200 and 500 °C and the total conductivity was measured. An enhanced conductivity value is observed which may make this system suitable for application as a solid electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs).     

Electrochemical studies on mixtures of LiNi0.8Co0.17Al0.03O2 and LiCoO2 cathode materials for lithium ion batteries

Detailed electrochemical investigations have been carried out on LiNi_0.8Co_0.17Al_0.03O₂ as cathode materials for lithium ion batteries in the potential range of 2.8-4.3 V. This sample showed an initial discharge capacity of 186 mAh/g which corresponds to 67% of its theoretical capacity. The effect of addition of LiCoO₂ to LiNi_0.8Co_0.17Al_0.03O₂ in the ratio 10:90, 30:70, 50:50 has been studied. The results showed that the addition of LiCoO₂ has improved the working voltage of the cell. In addition, the percentage retention (95%) of the cell is significantly increased in the composition ratio 50:50.     

Experimental and theoretical studies on dynamic properties of Li ions in LixMn2O4

In order to study the dynamic properties of Li_xMn₂O₄, potential relaxation techniques (PRT) is used to measure the chemical diffusion coefficient of Li_xMn₂O₄. Results are presented for x ranges from x=0.1 to 0.9. They show that the chemical diffusion coefficient at the two-phase coexistent stage near x=0.3 and 0.7 is higher than at the single-phase stage during the insertion and extraction process. Monte Carlo (MC) simulations are also used to simulate the ionic conductivity σ of Li ions in Li_xMn₂O₄ and its dependence as a function of lithium concentration x. The results show an M shaped curve in the plot of ionic conductivity σ versus x when the simulation temperature is 293 K, which confirms the experimental PRT results. The voltage profiles of Li_xMn₂O₄/Li cells were also simulated with different boundary conditions.     

Electrical behavior of BaZr0.1Ti0.9O3 and BaZr0.2Ti0.8O3 thin films

BaZr_0.1Ti_0.9O₃ and BaZr_0.2Ti_0.8O₃ (BZT) thin films were deposited on Pt/Ti/LaAlO₃ (1 0 0) substrates by radio-frequency magnetron sputtering, respectively. The films were further annealed at 800 °C for 30 min in oxygen. X-ray diffraction θ-2θ and Φ-scans showed that BaZr_0.1Ti_0.9O₃ films displayed a highly (h 0 0) preferred orientation and a good cube-on-cube epitaxial growth on the LaAlO₃ (1 0 0) substrate, while there are no obvious preferential orientation in BaZr_0.2Ti_0.8O₃ thin films. The BaZr_0.1Ti_0.9O₃ films possess larger grain size, higher dielectric constant, larger tunability, larger remanent polarization and coercive electric field than that of BaZr_0.2Ti_0.8O₃ films. Whereas, BaZr_0.1Ti_0.9O₃ films have larger dielectric losses and leakage current density. The results suggest that Zr⁴⁺ ion can decrease dielectric constant and restrain non-linearity. Moreover, the enhancement in dielectric properties of BaZr_0.1Ti_0.9O₃ films may be attributed to (1 0 0) preferred orientation.     

A new sodium samarium borate Na3Sm2(BO3)3

A new sodium samarium borate with composition Na₃Sm₂(BO₃)₃ (NSBO) has been synthesized by high temperature solid state reaction. The yellowish transparent single crystals of Na₃Sm₂(BO₃)₃ have been grown from the Na₂CO₃-H₃BO₃ flux system using the top-seeded solution growth (TSSG) method. X-ray diffraction analysis demonstrated that the NSBO crystals belong to orthorhombic systems and lattice parameters are a=5.0585 Å, b=11.0421 Å, c=7.0316 Å. The measurement of the infrared spectrum indicated that the basic anionic groups are the BO³⁻₃ groups. Furthermore, Na₃Sm₂(BO₃)₃ exhibits an optical second harmonic generation effect which is close to that of KDP (KH₂PO₄).     

Multiferroic properties of Bi0.8La0.2FeO3/CoFe2O4 multilayer thin films

Bi_0.8La_0.2FeO₃/CoFe₂O₄ (BLFO/CFO) multilayer thin films (totally 20 layers BLFO and 19 layers CFO) were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition. X-ray diffraction and transmission electron microscope measurements show that the films are polycrystalline and consisted of multilayered structure. Ferroelectric hysteresis loops with remnant polarization and saturated polarization of 4.2 and 13.3 μC/cm², respectively, were observed. On the other hand, the films show well-shaped magnetization hysteresis loops with saturated and remnant magnetization of 34.7 and 11.4 emu/cm³, respectively, which are significantly larger than pure BLFO thin films deposited under the same conditions. These results indicate that constructing epitaxial superlattice might be a promising way to fabricate multiferroics with improved properties.     

Neutron powder diffraction study of the Nd(Ba1−xNdx)2Cu3O7+δ solid solution

The Nd(Ba_1−xNd_x)₂Cu₃O_7+δ solid solution, Nd123ss, has been investigated by neutron powder diffraction and Rietveld analysis. It is confirmed that the crystal structure of its Nd-rich limit, Nd(Ba_0.55Nd_0.45)₂Cu₃O_7.33, is satisfactorily described in the space group Bmmm (a=7.7679(3), b=3.8542(1), and c=22.9590(9) Å). The fourfold superstructure with respect to the orthorhombic cell of YBCO is due to ordering between Ba and Nd atoms in the bridging layer. Differences with previous works concern exclusively the distribution of O atoms in the ‘chain’ layer. Our results give strong indications that ordering also occurs for lower Nd contents.     

Structure and electrical conductivity of a novel inorganic solid electrolyte: Na14.5[Al(PO4)2F2]2.5[Ti(PO4)2F2]0.5 (NATP)

A novel inorganic solid electrolyte with a layered framework structure stable up to 1043 K, Na_14.5[Al(PO₄)₂F₂]_2.5[Ti(PO₄)₂F₂]_0.5 (NATP), has been hydrothermally prepared and characterized by single-crystal and powder X-ray diffraction techniques, X-ray fluorescence (XRF) analysis, IR spectroscopic measurement, thermogravimetric and differential thermal analysis (TGA and DTA). NATP crystallizes in the acentric hexagonal space group P3 with a=10.448(2), b=10.448(2), , Z=1, containing a large number of Na⁺ cations in the interlamellar space and the cavities of its framework. There are six different crystallographic Na⁺ cationic sites, in which 8% Na(5) and 12% Na(6) sites are vacant. Electrical conductivity measurements show that Na⁺ cations exhibit a high mobility with two domains for the electrical conductivity versus temperature.     

Oxygen adsorption on the surface of In2O3 and β-(Ga0.8In0.2)2O3 mixed oxides porous structure

The paper is devoted to the oxygen sensing properties of In_1.2Ga_0.8Se₃ own oxide. The results are compared with theoretical adsorption kinetics. Temperature and time dependences of adsorption mechanisms are discussed.     

Supercapacitive cobalt oxide (Co3O4) thin films by spray pyrolysis

Uniform and adherent cobalt oxide thin films have been deposited on glass substrates from aqueous cobalt chloride solution, using the solution spray pyrolysis technique. Their structural, optical and electrical properties were investigated by means of X-ray diffraction (XRD), scanning electron micrograph (SEM), optical absorption and electrical resistivity measurements. Along with this, to propose Co₃O₄ for possible application in energy storage devices, its electrochemical supercapacitor properties have been studied in aqueous KOH electrolyte. The structural analysis from XRD pattern showed the oriented growth of Co₃O₄ of cubic structure. The surface morphological studies from scanning electron micrographs revealed the nanocrystalline grains alongwith some overgrown clusters of cobalt oxide. The optical studies showed direct and indirect band gaps of 2.10 and 1.60 eV, respectively. The electrical resistivity measurement of cobalt oxide films depicted a semiconducting behavior with the room temperature electrical resistivity of the order of 1.5 × 10³ Ω cm. The supercapacitor properties depicted that spray-deposited Co₃O₄ film is capable of exhibiting specific capacitance of 74 F/g.     

Electrical properties of pulsed laser-deposited SrxBiyTa2O9 thin films on Bi/Sr ratios

The dependence of the electrical properties of Sr_xBi_yTa₂O₉ thin films on the (Bi/Sr ratio 1.6, 2.3, 2.8, 3.4) has been investigated. The Sr_xBi_yTa₂O₉ ferroelectric thin films were synthesized on Pt/Ti/SiO₂/Si substrates using the pulsed laser deposition method. Saturation polarization (P_st) and coercive field (2E_c) depend on the Bi/Sr ratio. P_st increases while E_c decreases with an increase in Bi/Sr ratio. Atomic Force Microscopy images show that the grain size grows with increasing Bi/Sr ratio. It is observed that the impedance behavior in Sr_xBi_yTa₂O₉ thin film, conforms to the Constant Phase Element (CPE) model. It is believed that the diffuse charges at the grain boundary build up a surface polarization because the impedance behavior close to pure capacitor with grain size increased.     

Hydrothermal synthesis and electrochemical characterization of VO2 (B) with controlled crystal structures

Three different VO₂ (B) nanostructures, including urchin-like VO₂ (B), VO₂ (B) honeycombs and VO₂ (B) nanorods have been successfully fabricated through hydrothermal process by adjusting the concentrations of the oxalic acid. The microstructure and morphology of the VO₂ nanostructures were evaluated by using X-ray diffraction and scanning and transmission electron microscopies. Electrochemical properties measurements of urchin-like VO₂ (B) and VO₂ (B) honeycombs showed excellent cycling performance, especially the urchin-like VO₂ (B) exhibited higher discharge capacity and better capacity retention.     

A high-throughput search for direct methanol fuel cell anode electrocatalysts of type PtxBiyPbz

We used a high-throughput method to screen for direct methanol fuel cell anode electrocatalysts in the Pt-Bi-Pb system. Previous studies showed that PtBi and PtPb (both NiAs structure type) were active electrocatalysts for the oxidation of formic acid, but only PtPb was active in oxidizing methanol. We synthesized thin films with continuous composition spreads of the three elements by magnetron sputtering at deposition temperatures from ambient to 510 °C. A fluorescence method was then used to identify compositions that were active toward methanol oxidation. Only films deposited between temperatures of 160 and 400 °C showed electrocatalytic activity. The areas that were active for methanol oxidation showed predominantly the NiAs structure type according to XRD, with optimal activity for compositions near PtBi_0.01Pb_0.53.