Mixed-conducting ceramic oxides have potential uses in high-temperature electrochemical applications such as solid oxide fuel cells, batteries, sensors, and oxygen-permeable membranes. The Sr-Fe-Co-O system combines high electronic/ionic conductivity with appreciable oxygen permeability at elevated temperatures. Dense ceramic membranes made of this material can be used to separate high-purity oxygen from air without the need for external electrical circuitry, or to partially oxidize methane to produce syngas. Samples of Sr2Fe3-xCoxOy (with x = 0,0.6,1.0, and 1.4) were prepared by solid-state reaction method in atmospheres with various oxygen partial pressures (pO2) and were characterized by X-ray diffraction, scanning electron microscopy, and electrical conductivity testing. Phase components of the sample are dependent on cobalt concentration and pO2. Electrical conductivity increases with increasing temperature and cobalt content in the material.

The potential applications of mixed-conducting ceramic oxides include solid-oxide fuel cells, rechargeable batteries, gas sensors and oxygen-permeable membranes. Several perovskite-derived mixed Sr-Fe-Co oxides show not only high electrical-conductivity but also appreciable oxygen-permeability at elevated temperatures. For example, dense ceramic membranes of SrFeCo0.5O3-δ can be used to separate oxygen from air without the need for external electrical circuitry. The separated oxygen can be directly used for the partial oxidation of methane to produce syngas. Quantitative phase analysis of the SrFeCo0.5O3-δ material has revealed that it is predominantly composed of two Sr-Fe-Co-O systems, Sr4Fe6-xCoxO13 and SrFe1−xCoxO3-δ. Here we report preliminary structural findings on the SrFe1−xCoxO3-δ (0 ≤ x ≥ 0.3) system.

A novel design for a high temperature SOFC, based on lamellar electrode-electrolyte segments obtained by solidification of an oxidic eutectic melt on an electrolyte substrate is presented. Such “composite” electrodes contain NiO or MnO - 8Y-ZrO2 lamellae, which after reduction / oxidation yield electrode-electrolyte lamellae with 1–2 μm width and a vertical dimension of> 100 μm, depending upon the amount of eutectic melt solidified on a polycrystalline substrate. The nucleation of the eutectic on a polycrystalline substrate followed by a semi-directional crystallization of the two phases yields a gradient of 3-phase boundaries over the height of such an electrode, with the number of 3-phase boundaries increasing towards the substrate.

We investigated a composite electrolyte for solid oxide fuel cells prepared by coating a ceria sheet (Ce0.8Gd0.2O2-d or GDC ) with a scandia alumina doped zirconia (0.850ZrO2-0.110Sc2O3-0.04Al2O3) film by the sol-gel method. The sol-gel film annealed at 1200°C was examined by X-ray diffraction analysis and found to be in a cubic phase at room temperature. The ionic conductivity of this film is comparable to that of bulk sintered at 1620°C. Scanning electron microscope observations revealed that the film forms a good interface with the electrolyte of the ceria sheet, even though the annealing temperature is as low as 1200°C.

We fabricated a single cell consisting of a composite electrolyte, a La0.8Sr0.2MnO3 cathode and a Ni-YSZ anode. The composite electrolyte consisted of zirconia film about one micron thick deposited by the sol-gel method and a 0.2 mm thick ceria sheet.

A cell operated with moist H2 and O2 gas exhibited an open circuit voltage of 1.00 V at 800°C. This value is much closer to the value of 1.13 V expected from the Nernst equation than the value of 0.76 V for a cell with a ceria sheet but without the sol-gel film.

Brownmillerite(Ca2Al2O5-Ca2Fe2O5 solid solution) structure can be regarded as an oxygen-ion deficient perovskite structure. Because of high proportion of the oxygen vacancies in the structure, this material could be a candidate of fast oxide-ion conductor. Goodenough et al. indeed observed a first-order transition to a fast oxide-ion conductor at 930° C for Ba2In2O5 which adapts brownmillerite structure at ambient temperature. Molecular dynamics simulation was employed to study oxygen ion diffusion and phase transition of Ba2In2O5. The structure was well simulated at 300 K. When the system was heated, the original orthogonal cell transformed to a tetragonal cell at 2300 K. Inspection of the structure revealed that oxygen ions started to migrate from their original sites to nearest vacant oxygen sites at this temperature. The diffusion was restricted for the oxygen sites around In-tetrahedron, resulting highly anisotropie diffusion on the ac plane. At 4600 K it further transformed to an oxygen vacancies-disordered cubic perovskite structure. Although predicted transition temperature were apparently overestimated, the transition way to the phases with high oxygen ion diffusivity is consistent with the experimental results from electrical conductivity measurements. The high temperature cubic phase shows large ion conductivity. It is of interest to examine whether or not the cubic phase stabilizes in the low temperature region by making solid solution of another elements. We found that the cubic phase is stabilized below 500° C without any decrease of conductivity in BaIn1.9Ce0.1Oy and Ba2In1.8Nb0.2O5.

The dynamics of the doped perovskite-based high-temperature protonie conductors (HTPC) were studied by means of neutron vibrational spectroscopy (NVS) and first-principles pseudopotential supercell calculations. Vibrational spectra from hydrogen-charged samples with different rare-earth dopants revealed three well-defined vibrational bands in the energy ranges 20–60, 60–90, and 100–140 meV. The two lowest-energy bands were insensitive to the dopants. First-principles phonon calculations indicate that they are mainly associated with oxygen modes. In contrast, the high-energy band was very sensitive to the dopant, and in this case, calculations indicate that it is associated with OH bending modes.

A new design of interconnections between air electrodes and alloy separators in planar stacks is presented. The edges of the air electrodes supporting the electrolyte films are connected, through thin LaCrO3 layers, with the edges of adjacent alloy separators. The electric current in the cell flows radially in the porous thick air electrodes of LSM. The LaCrO3 layers are connected with the alloy separators through nickel felt in the fuel gas atmosphere. By using these interconnections, we can overcome the corrosion problems caused by contacting air electrodes with alloy separators in conventional planar stacks.

It is important for the commercialization of molten carbonate fuel cell (MCFC) to improve the endurance and the reliability of the electrolyte plate. The electrolyte-loss in the electrolyte plate increases the cell resistance and deteriorates the cell voltage. The formation of cracks in the electrolyte plate causes a gas cross leakage between the fuel gas and the oxidizer gas. The pore structure of electrolyte plate must be stable and fine to support liquid electrolyte under MCFC operation. It is necessary to prevent the formation of cracks in electrolyte plate during thermal cycling. We have improved the stability of electrolyte plate using advanced LiAIO2 powder and improved the durability of electrolyte plate for thermal cycling by the addition of the ceramic fiber.

The initial cell voltage using electrolyte plate with advanced LiAIO2 powder was 820mV at current density 150mA/cm2 and the decay rate of cell voltage was under 0.5%/1000h for 8,800h. According to the post analyses, the pore structure of the electrolyte plate did not change. The stability of advanced LiAIO2 powder was confirmed. It was proved that the electrolyte plate reinforced with ceramic fiber is effective for thermal cycling.

This research effort sought to demonstrate that combining select phosphonic acid additives with Nafion could improve Nafion's high temperature electrochemical performance. A 1:1 mixture of the additive with Nafion, resulted in a film that demonstrated 30% higher conductivity than a phosphoric acid equilibrated Nafion control at 175°C. This improvement to the high temperature conductivity of the proton exchange membrane Nafion is without precedent. In addition, thermal analysis data of the test films suggested that the additives did not compromise the thermal stability of Nafion. The results suggest that the improved Nafion proton exchange membranes could offer superior electrochemical performance, but would retain the same degree of thermal stability as Nafion. This research could eventually lead to portable fuel cells that could oxidize unrefined hydrocarbon fuels, resulting in wider proliferation of fuel cells for portable power.

Molecular mobility of water and trimethoxymethane (TMM) in NAFION membranes of two different equivalent weights (EW), 1100 and 1500, were investigated. Self-diffusion coefficients were determined by the NMR pulsed field gradient method, using the water and methyl protons NMR signals, in saturated NAFION samples containing concentrations of TMM in water varying between 0.5 and 14 M, and at temperatures varying from 30°C to 80°C. Diffusion of molecular species containing methyl protons is more than a factor of two slower in the 1500 EW membrane than in the 1100 EW membrane at 30°C and 1 M concentration. The difference rises to about a factor of four at 80°C and 14 M concentration. These differences are attributed to the lower extent of plasticization of the higher EW material as well as the greater effective distance between acid functional groups. NAFION samples containing methanol/water mixtures were also investigated. Comparison with the methanol results and the permeation behavior, as characterized by gas Chromatographie methods, show that more than half of the TMM is hydrolyzed to methanol as it passes through the acidic membrane. The implications of these findings for alternative fuels in direct oxidation fuel cells are discussed.

The high temperature corrosion of stainless steels (SUS316L and SUS310S) in the presence of molten carbonate [(Li0.62K0.8)2CO3 and (Li0.52Na0.48)2CO3] has been studied in a CO2-O2 atmosphere by measuring the weight gain of the specimens.

The corrosion of SUS316L significantly depended on the reaction conditions. With the carbonate coating (both Li/Na and Li/K carbonates), severe corrosion occurred during the initial period of the corrosion test below 923 K, especially around 823 K. The initial severe corrosion was a local corrosion which produced through holes in the metal specimens and occurred more clearly at low Pco2 with the Li/Na coating than with the Li/K coating. The corrosion became more severe at higher CO2 pressures and lower O2 pressures. In a pure CO2 atmosphere (without O2), the corrosion rate significantly increased at 823 K. The steel was corroded uniformly at that time.

In this work the CSGP was applied for preparation of Pt-WOx and its coatings on carbon black, silver and titan substrates. Saturated tungsten sol (0.15M) was prepared by dissolving (NH4)4W5O17 2.5 H2O in ascorbic acid solution. To this solution H2PtCl6 was added to obtain the molar ratio Pt:W=l. After evaporation and heating at 700°C for 2h homogeneous yellow-green powders were obtained. Another part of this solution was diluted with ethanol and after ultrasonic mixing used for preparation of coatings on Ag and Ti substrates by the immersion technique. Gel layers were dried at 200°C for 20h and then calcined at 700°C for 2h. The resulting white colored layers (thickness 10–65μm) were very adherent. Ascorbate aqueous tungsten-platinum sol diluted to 0.03 or 0.06 M ΣMe was used for preparation of Pt-W (10 and 20 %) catalyst by impregnation of carbon black Vulcan XC-72, followed by thermal treatment in air, argon and hydrogen atmospheres.

The current major cost component for proton exchange membrane fuel cells is the bipolar plate. An option being explored for replacing the current, nominal machined graphite component is a molded carbon fiber material. One face and the volume of the component will be left porous, while the opposite surface and sides are hermetically sealed via chemical vapor infiltration of carbon. This paper will address initial work on the concept.

The oxygen permeation through an oxide membrane with bulk composition SrFeCo0.5O3.25-δ has been measured as a function of both oxygen partial pressure and temperature. The results of the pressure dependence of the permeation indicate that the oxygen transport in this membrane is dependent primarily on the bulk diffusion rate. Although the permeation experiments were carried out at temperatures within, or very close to, the range where SrFeCo0.5O3.25-δ is stable as a pure single phase, the membrane was found to consist of SrFe1.5-xO3.25-δ(x = ∼0.42) together with fractions of Sr(Co,Fe)O3-δ perovskite and Co-Fe oxide that formed as stable phases during densification of the membrane at high temperature (1090°C). These additional phases persisted in the membrane during the permeation measurements.

A new process has been developed for the synthesis of well-crystallized Li-Mn-O spinels with a homogeneous composition Li[LixMn2-x]O4 (0.0≤x≤0.333) using the stoichiometry mixtures of lithium acetate and manganese nitrate as starting materials. The crystal structure of these compounds was studied with Rietveld refinements of the X-ray diffraction profiles. The lattice parameter of the spinels shows a strong dependence on the composition and manganese oxidation state. SEM micrographs indicate that the crystallites appear as single crystals. The size of the crystallites are in the range of 0.1 – 2μm, depending on the synthesis conditions. Samples with x≤0.125 show good electrode performance for the cell Li/Li1+xMn2-xO4 in the 4V region, whereas Li4Mn5O2 (x=0.333) spinels show good cyclability with a rechargeable capacity of over 100mAh/g in the 3V region.

The electrochemical reduction of the oxocarbons: squarate, croconate and especially rhodizonate lithium salts have been studied in all solid state lithium batteries. Lithium rhodizonate cells were tested on cycling in the 1.5 – 3.5 V potential range The reduction of lithium rhodizonate occurs in two waves of two electrons. The number of electrons transferred in reduction on the first cycle was around 3.5 based on a capacity of 515 mA.h.g−1 and a discharge depth of 87 %. This process is quite reversible but we observed a fast decline of the capacity on cycling. This loss of capacity may be attributed to residual water in the salt. The reduction of the lithium croconate occurs at a potential of 1.8 V in a quasi-irreversible process. We could not observe the reduction of lithium squarate which occurs in the potential range where the lithium is inserted in carbon black. We also report an investigation on rhodizonate salts of transition metals. The best results, in term of capacity, on the 1.5 – 3.5 V potential range, were obtained with copper rhodizonate which exhibits a capacity of 579 mA.h.g−1 on the first discharge.

LixMn2O4 materials are of considerable interest in battery research and development. The crystal structure of this material can significantly affect the electrochemical performance. The ability to monitor the changes of the crystal structure during use, that is during electrochemical cycling, would prove useful to verify these types of structural changes. We report in-situ XRD measurements of LiMn2O4 cathodes with the use of an electrochemical cell designed for in-situ X-ray analysis. Cells prepared using this cell design allow investigation of the changes in the LiMn2O4 structure during charge and discharge. We describe the variation in lattice parameters along the voltage plateaus and consider the structural changes in terms of the electrochemical results on each cell. Kinetic effects of LiMn2O4 phase changes are also addressed. Applications of the in-situ cell to other compounds such as LiCoO2 cathodes and carbon anodes are presented as well.

LiMn2O4 has a phase transition at room temperature, which is caused by Jahn-Teller distortion. DC resistivity of LiMn2O4 shows an anomaly at the transition temperature, while no such anomaly is observed in samples with excess lithium. X-ray diffraction patterns of LiMn2O4reveal that the crystal structure changes from cubic at higher temperature to orthorombic, as a first approximation, at lower temperature. However, no differences in initial charge-discharge curve are observed, which means that the Jahn-Teller distortion has no effect on electrochemical characteristics. The authors have succeeded in mass-producing lithium ion secondary batteries with a manganese spinel cathode.

We report on the use of pulsed laser depositon (PLD) to grow thin films of LiCoO2 on a number of low cost substrates including SnO2 coated Upilex, stainless steel and SnO2 coated glass. Highly textured (001) films grown on CVD deposited SnO2 films on 7059 glass, were obtained at 200 to 500 mTorr O2 and a temperature of 500 C. Similar texture was not obtained on the stainless or Upilex however dense films from crystalline to amorphous were obtained. The films were characterized by x-ray diffraction and Raman spectroscopy.

The optimum conditions for preparing LiNiO2 with good electrochemical performance are presented. Three different methods were investigated:

• LiOH and NiO at700°C in air(Batch A),

• LiOH and NiO between 150 and 750 °C in oxygen (Batch B), and

• LiNO3 and NiCO3 between 600 and 750 °C in oxygen (Batch C).

Batch C exhibited the highest first discharge capacity of about 150 mAh/g between 2.0 and 4.0V with a solid state Li/LiNiO2 cell containing a PAN-based polymer electrolyte. Solid state carbon/LiNiO2 cells and two-cell bipolar batteries demonstrated high rate capabilities at room temperature with an ability to sustain pulsed discharge currents as high as 50 mA/cm2. About 22 500,13 000, and 1000 pulses were obtained at current densities of 10, 20, and 50 mA/cm2, respectively, with a 10 ms pulse width followed by a 50 ms interpulse rest period.