In the single-step SOFC co-firing process YSZ electrolytes with sintering aid densify at a temperature of ˜1300°C. Electrodes employed in the single-step co-fired SOFC must therefore sinter with the right microstructure at ˜1300°C. Calcium-doped lanthanum ferrite, La0.8Ca0.2FeO3±δ (LCF-20) was identified in earlier studies as a possible stable cathode material for the single-step co-fired SOFC. LCF-20 is also expected to be a more stable cathode material than LSCF (strontium and cobalt doped lanthanum ferrite). Four-probe conductivity tests yielded ˜93 S/cm at 800°C and showed an increase in conductivity as pO2 increases, characteristic of p-type conduction. LCF has a higher electrical conductivity compared to LSCF and LCM+YSZ cathode materials. Oxygen ion conductivity of LCF-20 obtained from permeability measurements is higher than that of YSZ and LSF-20. Therefore LCF has excellent mixed conducting properties to serve as a catalytically active cathode material for co-fired solid oxide fuel cells operating at intermediate temperatures. Electrochemical Impedance Spectroscopy (EIS) measurements were made on symmetrical cells fabricated with YSZ electrolyte and the electrode materials. A gadolium doped ceria (GDC) barrier layer was employed to prevent LCF/YSZ reaction. Comparison of LCF/GDC/YSZ/GDC/LCF EIS data to LCM+YSZ/YSZ/LCM+YSZ EIS data gathered using identical test conditions and electrode microstructures shows that LCF has a measured polarization resistance (Rp) of approximately half that seen in LCM+YSZ. Variations in cathode thickness and porosity show the best performance with a cathode of a critical thickness and finer porosity. Slight stoichiometric deviations in LCF result in the formation of a Ca-Fe-O liquid phase during electrode sintering at around 1220 C. The liquid phase migrates into and through the GDC layer. EDX line scans show the second phase to be rich in Ca and Fe. Thicker GDC layers seem to prevent the liquid phase from reaching the electrolyte/GDC interface. Structural analysis with TEM will be performed. The properties and the effect of the Ca-Fe-O phase on the cathodic performance of the cell are being investigated; however, preliminary results indicate that minor amounts of the Ca-Fe-O phase will not interfere with the electrochemical performance of the LCF cathode. The high temperature instability in LCF has been observed in other studies, but has not been studied specifically in the literature.

BaCe0.25Zr0.60Co0.15O3-x (BCZC) was synthesized via oxalate co-precipitation route. Material was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Catalytic activity of BCZC with respect to hydrogen generation via methanol partial oxidation was determined. Conductivity of the material at different temperatures and under different environments was determined by AC impedance spectroscopy. XRD and TEM results indicated that BCZC was synthesized as a homogeneous cubic phase material. Catalyst tests indicated that BCZC was catalytically active towards hydrogen generation and AC impedance results were positive enough to warrant further electrochemical studies.

As MEMS devices for biomedical and other applications continue to develop and decrease in dimensions, the demand for power supplies with the appropriate size and energy density continues to grow. Although energy density is an important factor, one of the most crucial factors is the ability to fabricate cells in a variety of shapes so to enable the greatest design flexibility when fabricating a device. Recently our group has introduced an electrochemically self formed battery to grant a path towards the greatest flexibility. In short, a nanocomposite of an alkali halide such as lithium iodide is placed between current collectors and polarized thereby creating a lithium anode and polyiodide cathode in-situ. As with primary lithium-iodine cells the transport within the cathode is a complex mechanism involving the Li+, I-, and e- all within the polyiodide network. After our recent work on in-situ EIS evaluation of the technology, we have launched on an effort to greater understand the limiting transport mechanisms in the positive electrode as a function of polyiodide network development. An in-depth characterization study was performed on the LiI-I2-PVP-H20 at various molar ratios to understand the structural and conductivity changes that take place during formation of the cell A combination of AC impedance and DC polarization studies were used for the impedance characterization in conjunction with blocking electrode methodology for separating the conductivity into its electronic and ionic portions. Also, FTIR and Raman were used to structurally characterize the samples for both the polyiodide formation and the interaction between the polyiodides and polyvinylpyrrolidone (PVP). Being non conjugated, PVP was chosen as it does not intrinsically contribute to the conductivity of the composite but does induce the formation of polyiodide species. As different molar ratio composites are prepared, the concentration of different polyiodide species (I3-, I5-, In-) within the composite change and affect the overall conductivity. A 3-dimensional plot of composite conductivity reveals a high electronic conductivity ridge for samples containing either LiI anhydrous or monohydrate at a constant I2 to PVP ratio. These 3-dimensional plots also allow us to correlate represent in an ex-situ format the electronic and ionic conductivity of the cathode/electrolyte at various depths of discharge.

Using a model cathode-electrolyte system composed of epitaxial thin-films of La1-xSrxMnO3-δ (LSM) on single crystal yttria-stabilized zirconia (YSZ), we investigated changes in the cation concentration profile in the LSM during heating and under applied potential using grazing incidence x-rays. Pulsed laser deposition (PLD) was used to grow epitaxial LSM(011) on YSZ(111). At room temperature, we find that Sr segregates to form Sr enriched nanoparticles and upon heating the sample to 700°C, Sr is slowly reincorporated into the film. We also find different amounts of Sr segregation as the X-ray beam is moved across the sample. The variation in the amount of Sr segregation is greater on the sample that has been subject to 72 hours of applied potential, suggesting that the electrochemistry plays a role in the Sr segregation.

The defect structure, transport properties and band structure of the perovskite solid solution SrTi1-xFexO3-δ (STF) can be systematically controlled, over wide limits, by variation in the Fe fraction. In this paper, the authors review recent results which show that STF exhibits model mixed ionic-electronic conducting cathode behavior and extend the composition range investigated to include compositions from SrTiO3 rich values (x = 0.05) to SrFeO3-δ (x= 1). While the majority of the cathodes were prepared as dense films by pulsed layer deposition (PLD), selected compositions were also prepared by thermal inkjet printing. The cathodes were investigated by electrochemical impedance spectroscopy (EIS) as a function of electrode geometry, temperature and oxygen partial pressure. The electrode behavior was found to be controlled by surface exchange kinetics in almost all cases. Values for the surface exchange coefficient, k, were derived and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors such as (La,Sr)(Co,Fe)O3, thereby, confirming STF's suitability of as a model mixed conducting cathode material. Surprisingly, the magnitude of k was found to be only weakly dependent on the bulk electronic and ionic conductivities of STF which varied by many orders of magnitude (over nearly five orders of magnitude change in σel) over the x values examined in this study. The observed trends are discussed in relation to the known defect and transport properties of STF.

Blend membranes based on sulfonated polyetheretherketone (SPEEK) and containing 5 wt.% of silylated and sulfonated polyphenylsulfone (SiSPPSU) were prepared and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR) and by electrochemical impedance spectroscopy (EIS). Tests in a direct methanol fuel cell station were also performed. The experimental results demonstrated that the presence of hybrid polymer SiSPPSU allowed to increase the proton conductivity of electrolyte and to improve its performance under fuel cell operating conditions. Due to its satisfactory properties, SPEEK/ SiSPPSU blend membrane has a potential use in DMFCs operating at intermediate temperatures.

Materials of the La2/3-xLi3xTiO3–family have been studied by selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), powder synchrotron X-ray diffraction and powder neutron diffraction. HRTEM showed that the materials have a complex domain-microstructure. The size and shape of the domains have been obtained from synchrotron X-ray diffraction data; besides, other extended defects such as strains and compositional fluctuations have been detected. The complementary use of local (SAED and HRTEM) and average (SXRD and NPD) techniques have allowed us to propose a model to refine the crystal structure of these oxides also accounting for their microstructure. All these materials have a perovskite-related structure with a diagonal unit cell (≈√2ap x √2ap x 2ap) as a consequence of the tilting of the TiO6 octahedra. Ordering of lanthanum and lithium ions and vacancies along the 2ap-axis, as well as displacements of titanium ions from the centre of the octahedra, have been determined. The Li+ ions present a distorted square planar coordination and are located in interstitial positions of the structure, which could explain the very high ionic conductivity of this type of materials. The lithium conductivity depends on the oxide composition and its crystal microstructure, which varies with the thermal treatment of the sample.

The construction of interaction potentials for the Y0.5+0.25xNb0.25xZr0.5–0.5xO1.75 system, on a purely ab-initio basis, is described. These potentials accurately reproduce experimental data on both the structure and the dynamics of these systems; the computer simulations also reproduce the experimental trend of the conductivity, which decreases as x increases, and of the level of static disorder within the O2− sublattice, which increases with x. A detailed analysis of these phenomena shows that the static disorder in Y3NbO7 is caused by the high Nb5+ charge and that in this material the conduction is heterogeneous, i.e. some anions are completely immobile while some others are very mobile. The role of the cation sublattice is explained in detail.

It is recognized that hydrogen separation membranes are a key component of the emerging hydrogen economy. A potentially exciting material for membrane separations are bulk metallic glass materials due to their low cost, high elastic toughness and resistance to hydrogen ‘embrittlement’ as compared to crystalline Pd-based membrane systems. However, at elevated temperatures and extended operation times structural changes including partial crystallinity may appear in these amorphous metallic systems. A systematic evaluation of the impact of partial crystallinity/devitrification on the diffusion and solubility behavior in multi-component Metallic Glass materials would provide great insight into the potential of these materials for hydrogen applications. This study will report on the development of time and temperature crystallization mapping and their use for interpretation of ‘in-situ’ hydrogen permeation at elevated temperatures.

Structural features and transport properties of Fe- and Al-doped apatite-type lanthanum silicates were studied with relation to a role of the [SiO4] substructure. XRD, TEM, Mössbauer, UV-Vis electron, IR, 29Si and 27Al NMR spectroscopy were used for structural studies; impedance spectroscopy and oxygen isotope heteroexchange were used for transport properties characterization.

Dense and well-adhered CuMn1.8O4 spinel oxide coatings were successfully deposited on Crofer 22 APU stainless steel substrates by a cost effective electrophoretic deposition technique. Coated and uncoated Crofer substrates were oxidized for 120 hours in air at 800°C. A diffusion model was developed for the oxidation of the coated alloys, which predicted para-linear oxidation kinetics. The effective diffusivities in the coating and in the thermally grown oxide were calculated to be 2×10-15 cm2/s and 2.5×10-16 cm2/s respectively, at 800°C. Area specific resistances (ASR) of thermally cycled samples at 800°C did not show a significant difference compared to the isothermally oxidized sample for the same total oxidation time, suggesting good coating adherence. The ASR of the coated alloys is projected to be around 3.8×10-2Ωcm2 after 50000 at 800°C in air, making them excellent candidates for interconnect applications for solid oxide fuel cells operated at 800°C or lower.

The segregated vacancies in the A site-ordered oxygen-deficient double perovskites REBaCo2O5+x (RE = La, Pr, Nd, Sm, Eu) (RBCO) are thought to greatly enhance the diffusivity of oxide ions in the bulk of these materials and possibly supply surface defect sites with enhanced reactivity towards molecular oxygen. Some materials in this family of REBaCo2O5+x compounds, such as PrBaCo2O5+x, (PBCO), have already demonstrated high electronic conductivity, rapid oxygen ion diffusion and surface exchange kinetics. Therefore, the family of REBaCo2O5+x compounds were synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (SOFCs) based on gadolinium doped ceria (CGO) electrolytes. The electrochemical performance of symmetrical cells (REBaCo2O5+x + CGO composite cathodes on the CGO electrolytes) was evaluated by using AC impedance spectroscopy. The area specific resistance (ASR) performance was measured as a function of temperature as well as oxygen partial pressure.

Sulfonated polyether ether ketone (SPEEK)-based composite membranes doped with 23 and 50 wt% of hydrated tin oxide (SnO2·nH2O) were prepared and characterized for Direct Methanol Fuel Cell (DMFC) applications . The composite membranes were characterized in terms of ion exchange capacity (IEC), tensile tests, water uptake measurements, electrochemical impedance spectroscopy (EIS), and Pulsed-field-gradient spin-echo nuclear magnetic resonance (PFGSE NMR) spectroscopy. The body of results indicated the involvement of hydrated tin oxide in the proton conduction mechanism, the inorganic phase providing additional paths between the water clusters for proton transport. NMR measurements evidenced that SnO2·nH2O particles not only facilitate the proton transport but also hinder water diffusion. Therefore, due to the selectivity of SnO2·nH2O for proton diffusion, the filler effect was found to be also beneficial for the reduction of methanol crossover through the SPEEK membrane and for improving the performance of the SPEEK membrane when used as electrolyte in a DMFC test station.

Ionic and mixed conducting oxides (La0.9Sr0.1)[(Ga1-xFex)0.8Mg0.2]O3-y (I) and (Sr1.8La0.2)(GaFe)O5.1 (II) with the perovskite and brownmillerite structures, respectively, have been prepared in forms of dense bulk ceramics and ceramic coatings by the sol-gel method. Thin films II have been grown by the pulsed laser deposition method on single crystal MgO (100) and Si (100), fused silica, and stainless steel substrates. The films grown under optimal process conditions were single-phase and homogeneous, with a high degree of preferential orientation. The structure and microstructure of the ceramic coatings have been studied by X-ray diffraction and scanning electron microscopy.

Anode-supported planar solid oxide fuel cell (SOFC) was successfully fabricated by a single step co-firing process. The cell comprised of a porous Ni + yittria-stabilized zirconia (YSZ) anode support, a porous and fine-grained Ni + YSZ anode active layer, a dense YSZ electrolyte, a fine-grained porous Ca-doped LaMnO3 (LCM) + YSZ composite cathode active layer, and a porous LCM cathode current collector layer. The cell was tested between 700˜800oC with humidified hydrogen (97% H2+3% H2O) as fuel and air as oxidant. The measured maximum power densities were 1.42W/cm2 at 800°C, 1.20W/cm2 at 750°C, and 0.87W/cm2 at 700°C. The cell was also tested at 800oC with various compositions of oxidant, and cell parameters including the area specific ohmic resistance, exchange current density, and anodic and cathodic limiting current densities were determined using the polarization model and impedance spectroscopy.

Mixed conductive oxides are a topic of interest for applications in oxygen separation membranes as well as use in producing hydrogen fuel through the partial oxidation of methane. The oxygen flux through the membranes is governed both by the oxygen ionic conductivity as well as the material's electronic conductivity; composite membranes like Ce0.8Gd0.2O2-δ(CGO)-CoFe2O4 (CFO) use gadolinium doped ceria oxides as the ionic conducting material combined with cobalt iron spinel which serves as the electronic conductor. In this study we employ ˜ 50 nm sputtered CeO2 layers on the surface of porous CGO ceramic substrates which serve as solution ‘blocking’ layers during the thin film fabrication process facilitating the control of film thickness. Films with thickness of ˜ 2 and 4 microns were prepared by depositing 40 and 95 separate sol-gel layers respectively. Oxygen flux measurements indicated that the permeation increased with decreasing membrane thickness; thin film membrane with thickness on the micron level showed flux values an order of magnitude greater (0.03μmol/cm2 s) at 800oC as compared to 1mm thick bulk ceramic membranes (0.003 μmol/cm2).