Substitution effects of Ga and Al for Fe in (BaxSr1-x)0.98FeO3-δ were studied with respect to crystal structure, conductivity and oxygen permeability. The solubility limits of Ga and Al in (BaxSr1-x)0.98Fe1-yMyO3-δ (M=Ga, Al) were between 20 and 30 mol%. The substitution of Ga and Al caused decreases in electronic and oxide ionic conductivities (mixed conductivities) but the enhancement of the reduction tolerance. Sintered membranes of the Ga- and Al-substituted oxides showed oxygen permeability under the He/air oxygen partial pressure gradient and were stable under the condition of methane partial oxidation at 900 °C.

This work presents the last progresses in the development of thin oxidic proton conducting electrolytes supported on mixed conducting cermets making use of a solid state reaction. The procedure includes preparation routes applying solid state transformation of an already-gastight oxide layer (typically doped zirconia and ceria) by reacting with an alkali-earths layer (stoichiometric amount) deposited by screen printing on top of that. This kind of supported films can find application as IT-SOFC, H2-membranes and advanced catalytic converters. Thin-film (∼5μm) proton conducting membranes with the nominal composition as for instance BaZr0.85Y0.15O3-δ and BaCe0.8Gd0.2O3-δ were prepared over porous Ni-8YSZ or Ni-CGO substrates by solid state reaction. The produced films are gastight with a homogeneous composition, and showed a highly crystalline cubic perovskite structure. The solid state reaction promoted the formation of (i) a different grain size distribution from 0.1 μm for barium zirconate to 2-3μm for barium cerate, and (b) the formation of a porous fibrous top-layer (for barium zirconate) or a just flat surface (for strontium zirconate), depending on the exact composition of the reacting oxides.

Mixed-conducting oxides, possessing both ionic and electronic charge carriers, have found wide application in recent years in solid-state electrochemical devices that operate at high temperatures, e.g., solid-oxide fuel cells, batteries, and sensors. These materials also hold promise as dense ceramic membranes that separate gases such as oxygen and hydrogen from mixed-gas streams. We are developing Sr-Fe-Co oxide (SFC) as a membrane that selectively transports oxygen during partial oxidation of methane to syngas (mixture of CO and H2) because of SFC's high combined electronic and ionic conductivities. We have evaluated extruded tubes of SFC for conversion of methane to syngas in a reactor that was operated at ≈900°C. Methane conversion efficiencies were >90%, and some of the reactor tubes were operated for >1000 h. We are also developing dense proton-conducting oxides to separate pure hydrogen from product streams that are generated during methane reforming and coal gasification. Hydrogen selectivity in these membranes is nearly 100%, because they are free of interconnected porosity. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, we have developed cermet (i.e., ceramic-metal composite) membranes in which metal powder is mixed with these oxides in order to increase their hydrogen permeability. Using several feed gas mixtures, we measured the nongalvanic hydrogen permeation rate, or flux, for the cermet membranes in the temperature range of 500-900°C. This rate varied linearly with the inverse of membrane thickness. The highest rate, ≈32 cm3(STP)/min-cm2, was measured at 900°C for an ≈15-μm-thick membrane on a porous support structure when 100% H2 at ambient pressure was used as the feed gas.

We show in this paper the possibility of using mechanical milling to prepare apatite-type La, Nd and Gd silicates starting from stoichiometric mixtures of the constituent oxides. XRD patterns collected after grinding the starting mixtures for 9 hours contain only the characteristic reflections of the target materials with no other phase apparently present. Electrical conductivity data were successfully fitted to a Jonscher-type empirical expression with fractional exponent n included in the 0.35-0.75 range. Activation energies for oxygen migration were found to decrease as the size of the rare-earth cation increases. Therefore, the highest conductivity values were found for the apatite-type lanthanum silicate.

LiMn1.5Ni0.5O4 cathode material was prepared by sol-gel method and annealed at 850°C for 15 hrs. The prepared powder was coated with ZnO by dissolving zinc acetate in methanol and LiMn1.5Ni0.5O4 powder was mixed in this solution followed by the continuous stirring for 4 hr. The LiMn1.5Ni0.5O4 and ZnO coated LiMn1.5Ni0.5O4 powder was characterized using X-ray diffraction, TEM and Raman spectroscopy. The coin cell was fabricated using LiMn1.5Ni0.5O4 and ZnO coated LiMn1.5Ni0.5O4 as cathode materials, LiPF6, dissolved in EC/DMC (1:1 wt ratio) as electrolyte, and Li foil as anode. The cyclic voltammetric and charge-discharge characteristics were carried out for the coin cell using LiMn1.5Ni0.5O4 and ZnO coated LiMn1.5Ni0.5O4 cathode materials. It was found that the ZnO coated LiMn1.5Ni0.5O4 cathode materials showed improved discharge capacity (∼146mAh/g) as compared to the pure LiMn1.5Ni0.5O4 (∼140mAh/g). The discharge capacity retention after 50 cycles was found to be about 94% and 97% for LiMn1.5Ni0.5O4 and ZnO coated LiMn1.5Ni0.5O4 cathode materials, respectively.

Miniature solid oxide fuel cells (μSOFC) are very promising energy sources for portable devices. In this work we report on fabrication and on first experimental results of μSOFCs processed by means of silicon and thin film technology. All the layers involved in the PEN (Positive electrode-Electrolyte-Negative electrode) structure were sputter deposited on silicon wafer. The PEN membrane was liberated using deep silicon dry etching. The cathode is a combination of a very fine platinum grid covered by a thin LSC layer. The electrolyte is a bilayer of YSZ and CGO ionic conductors. Scanning electrons microscope and X-ray analysis show that the deposited films are polycrystalline with a columnar microstructure. The conductivities of these films are sufficiently high for cell operation at 550°C. The anode is composed of a NiO-Ni-CGO composite. A supporting structure consisting of an electroplated nickel grid is deposited on top of the anode and is part of it. The final PEN is a free standing 1 micron thick membrane, with a diameter of 5 mm. First measurements showed that this structure is mechanically stable up to 550°C and that the cell works with an OCV of 200 mV.

Lithium titanate spinel (Li4Ti5O12, or LTS) has received an increasing level of attention as a nanopowder lithium-ion battery anode. Nanopowder electrodes may provide a higher energy density than currently available. Furthermore, the surface of the spinel nanopowder has been studied in air, under vacuum, and at varying temperatures with diffuse reflectance infrared Fourier transform spectroscopy revealing surface hydroxyls, carbonates and water. Applying a TiN thin film, a film that is both conducting and chemically inert to harmful reactions with the solvent/electrolyte, by atomic layer deposition (ALD) may enhance battery cycle life. A 200-layer film was deposited at 500 °C. We have characterized the influence of a TiN thin film on Li-ion battery performance. Total nitrogen content and transmission electron microscopy were used to verify the presence of nitrogen and formation of a thin film, respectively, on LTS. Modifying the powder with an ALD thin film coating produced an anode material with a voltage profile that demonstrated longer charge maintenance with shorter transient periods. It also held a more consistent charge capacity over varying discharge rates in coin cell testing than unmodified LTS.

Fuel Cells are highly promising energy conversion systems for the new energy scenario. Particularly, Solid Oxide Fuel Cells (SOFCs) have been extensively studied during the last few years as a result of the increasing interest in the development of more efficient, and environmentally friendly ways of energy generation, as well as a consequence of their fuel flexibility. This work shows some strategies to improve the efficiency of SOFCs through the use of new anode materials, a novel method of microstructural optimisation by means of polymeric templates, using composites or cermets-based materials or applying a new concept in SOFC, e.g. the Symmetrical SOFC (SFC).

The thermodynamic properties of Ba2In2O5 are studied using Monte Carlo simulation of an ab initio based cluster expansion. The simulations predict a first-order orthorhombic to tetragonal phase transition, followed by a second-order tetragonal to cubic phase transition, which is in good agreement with experiments. It is predicted that the orthorhombic to tetragonal transition is associated with major disordering in the O(3) plane as well as some introduction of vacancies in the O(2) plane.

Dynamics of water in Nafion 117 membranes, in the acid form, at two hydration levels and several temperatures were investigated by means of dielectric relaxation spectroscopy in both, low (10−2 to 107 Hz, 25 to −80 °C) and microwave (0.045-26 GHz, 35 °C) frequency regions by employing different experimental setups. Three states of water were identified: a) strongly bound to the sulfonic groups (in agreement with other investigations) forming the first hydration layer; b) loosely bound, surrounding the first layer and c) free water, having similar dynamics as in the bulk state.

Silver vanadium oxide (SVO, Ag2V4O11) has demonstrated commercial success as a solid-state cathode material in power sources for implantable biomedical devices. This report describes the synthesis of SVO via a hydrothermal method. This novel synthetic approach allows low temperature production of acicular SVO nanofibers with a high surface area. This material was investigated as a cathode material in primary lithium batteries for high rate pulse applications.

We analyze in this work the influence of ordering on the oxygen ion dynamics in the ionic conductor Gd2(Ti0.65Zr0.35)2O7, prepared by mechanical milling. As-prepared powder phase presents a metastable anion deficient fluorite-type of structure below 800°C becoming a disordered pyrochlore above this temperature. Such phase transformation implies a significant increase in the ionic conductivity of this material as a result of a systematic decrease in the activation energy for the dc conductivity, from 1.23 to 0.78 eV. Electrical conductivity relaxation is well described by the Kohlrausch-Williams-Watts (KWW) stretched exponential function with the fractional exponent n decreasing systematically with increasing sintering temperature (increasing ordering) as a result of decreasing ion-ion interactions in better ordered samples.

Proton conductivity of yttrium-doped barium zirconate grown on MgO(100) using pulsed laser deposition (PLD) has been explored as a function of film thickness (60∼670nm) related to crystal and grain structure in the nano scale. Highly textured thin film (60nm) without significant grain separation showed high ionic conductivity close to the bulk BYZ value while thick polycrystalline samples showed lower values with clear grain and grain boundary formation.

Miniaturized single-chamber solid-oxide fuel cells (SC-SOFC) are a promising class of devices for portable power generation required in the operation of distributed networks of microelectromechanical systems (MEMS) in harsh environments. The single-face configuration, which consists of interdigitated (comb-like) array of electrodes on an yttria-stabilized zirconia (YSZ) electrolyte substrate, is of particular interest because of the ease of high-temperature microfluidic packaging and integration with MEMS. The primary design consideration for this configuration is the minimization of electrode widths and inter-electrode spacings to dimensions on the order of a few micrometers. This is necessary to minimize polarization resistance and increase fuel cell efficiency. Achieving these geometries using standard microfabrication methods is difficult because of the thickness, porosity, and complex chemistries of the electrodes. Here, we report the development of an innovative and rapid method for manufacturing SC-SOFCs with interdigitated electrodes using robot-controlled direct-writing. The main steps consist of: (i) formation of inks (or suspensions) using anode (NiO-YSZ) and cathode (lanthanum strontium manganite) powders, (ii) pressure-driven extrusion of inks through a micronozzle using a robot-controlled platform, and (iii) sequential sintering to form the fuel cell. The first-generation SC-SOFC device, with electrode widths of 130 μm and inter-electrode spacing of 300 μm, has been manufactured using direct-write microfabrication. The electrodes have been extensively characterized using electron microscopy and x-ray diffraction to assess porosity and to confirm phase identity. The primary process parameters in this approach are the particle size and size distribution, rheological properties of the suspension, extrusion pressure, nozzle size, stage velocity, and sintering conditions. As the first step in the development of detailed process-structure-performance correlations for the fuel cells, we have studied the effects of extrusion pressure (in the range 30-40 bar) and stage velocity (in the range 0.2-2.0 mm/s) on the geometry and size of electrodes, for fixed suspension viscosity and nozzle diameter. An optimal combination of speed and pressure has been identified and catalogued in the form of process maps. Similarly, the particle size distribution of the anode and cathode powders is found to have a significant effect on the microstructure, especially porosity, of the sintered electrodes. The implications of these results for the design of the next generation of SC-SOFC, with reduced electrode dimensions and improved electrochemical performance, will be discussed.

The carbon anode presently used in commercial lithium ion batteries has a relatively low capacity and may pose safety problems particularly under fast charging. Nanosized amorphous materials have excellent electrochemical behavior when applied as anodes for lithium ion batteries; especially they have advantages over bulk materials on capacity retention and rate capability. The initial studies on some amorphous compounds are promising. A commercialized tin-cobalt-carbon amorphous material, which is composed of ∼5nm nanoparticles, shows a capacity retention of >350 mAh/g for 50+ cycles. Manganese oxide nanofibers were synthesized by polymer templated electrospinning followed by calcinations. The fibers have 200-500 nm diameter and the main composition is Mn3O4. The capacity remains 400 mAh/g for at least 50 cycles.

We present the synthesis and characterization of a novel lithium iron polyphosphate LiFe2P3O10 prepared by wet-chemical technique from nitrate precursors. The crystal system is shown to be monoclinic (P21/m space group) and the refined cell parameters are a=4.596 Å, b=8.566 Å, c=9.051 Å and β=97.46°. LiFe2P3O10 has a weak antiferromagnetic ordering below the Néel temperature TN=19 K. Electrochemical measurements carried out at 25 °C in lithium cell with LiPF6-EC-DEC electrolyte show a capacity 70 mAh/g in the voltage range 2.7-3.9 V.

Anode-supported planar solid oxide fuel cell (SOFC) was successfully fabricated by a single step co-firing process. The cell comprised of a Ni + yittria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, a Ca-doped LaMnO3 (LCM) + YSZ cathode active layer, and an LCM cathode current collector layer. The fabrication process involved tape casting of the anode, screen printing of the electrolyte and the cathode, and single step co-firing of the green-state cells at 1300°C for 2 hours. The maximum power densities were 1.50W/cm2 at 800°C, and 0.87W/cm2 at 700°C with humidified hydrogen (97% H2-3% H2O) as fuel and air as oxidant. The experimentally measured I-V curves were fitted into a polarization model to obtain cell parameters including the area specific ohmic resistance, exchange current density, effective binary diffusivity of hydrogen and water vapor in the anode, and that of oxygen and nitrogen in the cathode. The cell was also tested at 800°C with various compositions of humidified hydrogen to evaluate the cell performance at high fuel utilization, and the maximum power densities were 1.30W/cm2 with 75.7% H2-24.3% H2O, 0.94W/cm2 with 49.4% H2-50.6% H2O, and 0.49W/cm2 with 27.3% H2-70.7% H2O.

The electrochemical properties of perovskite-type materials, Ln2NiO4+δ (Ln = La, Pr) as cathodes on Ce0.9Gd0.1O3 (CGO) and YSZ electrolytes were studied from 400 to 700 °C under different oxygen partial pressures (pO2 = 0.01-1 atm) by using AC impedance spectroscopy. These oxide electrodes yielded lower area specific resistance (ASR) compared to manganite perovskites. Ln2NiO4+δ (Ln = La, Pr) on CGO showed similar electrochemical performance though La2NiO4 (LNO) has a smaller ASR than Pr2NiO4 (PNO). The polarization resistance of LNO on YSZ was 2 orders higher than that on CGO. The interfacial resistance between the electrode and electrolyte was much smaller for LNO on CGO than for LNO on YSZ.

Two types of samples containing different La2/3-xLi3xTiO3 (LLT) solid electrolyte /LiCoO2 cathode interfaces were prepared by depositing LiCoO2 on polycrystalline LLT with two different surface finishes: cleaved and polished surfaces. Electrochemical properties of the samples were analyzed by cyclic voltammetry (CV). Microstructures of the LLT/LiCoO2 interfaces were investigated by scanning electron microscopy and transmission electron microscopy. Cyclic voltammograms of the cleaved sample show that the anodic and cathodic peaks respectively shift to higher and lower potential with the number of cycles, while those for the polished samples do not change much during cycles of potential sweeps, indicating the higher stability for the polished samples upon insertion and extraction of lithium ion. The LiCoO2 thin-film cathode is epitaxially deposited with the orientation relationships: {110}LLT//{1120}LiCoO2 and <001>LLT//<4401>LiCoO2 for both samples with different geometric configurations of the interfaces to the Li layers in the LiCoO2. Amorphous regions are observed to exist in places at the interface only in the polished samples. The geometric configuration of the interface and the existence of the amorphous regions are considered to have great influences on the stability of the LLT/LiCoO2 interfaces upon charge / discharge operations.

Analytical transmission electron microscopy (ATEM) was applied to investigate local variation of composition of transition metals in each particle of Fe-substituted Li2MnO3, which reveals high specific capacity and high voltage as a positive electrode. Crystal lattice images of primary particles were observed by means of high-resolution TEM (HRTEM), where local composition of Fe and Mn was determined by electron energy-loss spectroscopy (EELS). It was found that there exist both manganese (Mn)-rich and iron (Fe)-rich regions in a primary particle, where concentration of Fe and Mn fluctuates irregularly in nanometer scale. The relationship between composition and crystal structure in each local region is discussed.