A non-hydrolytic sol-gel approach for the preparation of MgxAl2(1-x)Ti(1+x)O5 powders

The study of non-hydrolytic reactions for the synthesis of MgxAl2(1-x)Ti(1+x)O5 solid solution with x = 0.6 is reported. The reagents chosen were Al(OsBu)(3), Ti(OiPr)(4), TiCl4 and Mg(NO3)(2).6H(2)O in toluene. The reactions were followed using C-13 Nuclear Magnetic Resonance (NMR) spectroscopy. Sol-gel synthesized powders were calcined in air at 300, 500, 1000, and 1200degreesC for 1 h. The powders were analysed by X-Ray Diffraction (XRD) demonstrating the formation of a Mg0.6Al0.8Ti1.6O5 phase in samples treated at the higher calcination temperature

Tailoring phase stability and electrical conductivity of Sr0.02La0.98Nb1–xTaxO4 for intermediate temperature fuel cell proton conducting electrolytes

Sr0.02La0.98Nb1–-xTaxO4 (SLNT, with x=0.1, 0.2, and 0.4) proton conducting oxides were synthesized by solid state reaction for application as electrolyte in solid oxide fuel cells operating below 600 °C. Dense pellets were obtained after sintering at 1600 °C for 5 h achieving a larger average grain size with increasing the tantalum content. Dilatometric measurements were used to obtain the SLNT expansion coefficient as a function of tantalum content (x), and it was found that the phase transition temperature increased with increasing the tantalum content, being T=561, 634, and 802 °C for x=0.1, 0.2, and 0.4, respectively. The electrical conductivity of SLNT was measured by electrochemical impedance spectroscopy as a function of temperature and tantalum concentration under wet (pH2O of about 0.03 atm) Ar atmosphere. At each temperature, the conductivity decreased with increasing the tantalum content, at 600 °C being 2.68×10−4, 3.14×10−5, and 5.41×10−6 Scm−1 for the x=0.1, 0.2, and 0.4 compositions, respectively. SLNT with x=0.2 shows a good compromise between proton conductivity and the requirement of avoiding detrimental phase transitions for application as a thin-film electrolyte below 600 °C

Effects of tin phosphate nanosheet addition on proton-conducting properties of sulfonated poly(ether sulfone) membranes

Organic/inorganic composite membranes were prepared by dispersing nanosheets of layered tin phosphate hydrate [Sn(HPO4)2·nH2O (SnP)] in sulfonated poly(ether sulfone) (SPES) at SnP contents of 0–40 vol.%. The stabilities and proton conductivities of SPES/SnP nanosheet (SnP-NS) composite membraneswere investigated and comparedwith those of SPES/SnP particle (SnP-P) composite membranes. The chemical stabilities as evaluated by thermogravimetry, differential thermal analysis, and diffuse reflectance Fourier-transform infrared spectroscopy were improved in both composite membranes. The improvement in the structural stability of SPES/SnP-NS composite membranes was more evident than that in SPES/SnP-P. The results suggest that exfoliation of SnP increases the area of the SPES–SnP interface and extends the connectivity of the network of hydrogen bonds. A composite membrane containing 10 vol.% SnP-NS (SPES/SnP-NS10vol.%) showed a high conductivity of 5.9×10−2 S cm−1 at 150 °C under saturated water vapor pressure. Although less water was present in SPES/SnP-NS10vol.% than in SPES/SnP-P10vol.% or pure SPES, the conductivity of SnP-NS10vol.% was the highest among these samples at 130 °C under a high relative humidity (RH). However at a low RH, the proton-conducting property was not improved by changing the composition of the SnP-NS. These results suggest that the hydrogen-bond network operates effectively for proton conduction at a high RH, but at a low RH, the network fails to conduct as a result of a decrease in water content accompanied by structural stabilization

Electrochemical characterization of anode supported SOFC prepared by co-firing technique

One of the main problems in the fabrication of anode supported solid oxide fuel cells is related to the sintering of electrolyte layer on anodic substrate, because differential densification of the layers may result in cracks during thermal process. Co-firing approach consists of simultaneous sintering of both electrolyte and anode. In this way, shrinkage of porous layer is compatible with the densification of electrolyte film. In this work co-firing technique was used for the sintering of YSZ thick films deposited on green NiO-YSZ layers by electrophoretic deposition (EPD). EPD is a colloidal process based on the motion of charged particles in the electric field in the direction of the electrode with opposite charge, thus forming a compact layer. With respect to other techniques, EPD has several advantages: short formation times, little restriction in the shape of substrates, simple deposition apparatus, possibility to have a mass production, low cost, easy control of the thickness of the deposited film through simple regulation of applied potential and deposition time. The EPD/co-firing combined process allowed to obtain a dense, 10 μm thick, crack free electrolyte layer with a good bonding to the anode. A slurry was prepared starting from a commercial NiOYSZ anodic powder (Praxair), polyvinylidene fluoride (PVDF binder SOLEF 6020, Solvay), a nanometric carbon powder (super P, Carbon Belgium), dispersed in N-methyl-2-pyrrolidone. A green membrane was obtained after evaporation of the solvent. A suspension of YSZ powder was prepared starting from commercial YSZ (TZ8Y, Tosoh) in methanol and deposited by EPD on a green NiO-YSZ membrane using a planar EPD cell setup. Co-firing parameters were assessed from the results of TG-DTA analysis performed on green bodies. Figure 1 shows the results of Hg porosimetry performed on sintered anodes for the determination of residual porosity and surface area. Green and fired samples were characterized in terms of morphology by scanning electron microscopy (FE-SEM), as reported in Figure 2. EDS linescan performed on the cross section of the cell did not show nickel diffusion in the electrolyte layer. A cathode layer was deposited on fully sintered half cells via spray-powder technique, using a suspension of commercial LSFC powder (Nextech), followed by a low temperature sintering process. Electrochemical characterization was performed on button cells in hydrogen in the temperature range 600-800 degrees C. Data of the electrochemical characterization will be presented at the conference

Yttrium doped Barium cerate and Zirconate heterostructures: deposition and electrochemical characterization

Epitaxial heterostructures consisting of an yttrium doped barium cerate (BCY) layer sandwiched between two yttrium doped barium zirconate (BZY) thin layers have been deposited on insulating (001) MgO substrates by pulsed laser deposition. The first BZY layer was aimed at improving the lattice match with the MgO substrate, the second at protecting the BCY layer. Ionic conductivity has been studied in the 300 – 600°C temperature range as a function of the BCY thickness. Due to the absence of blocking grain boundaries, heterostructures showed a conductivity larger than that of BCY pellets sintered under optimized conditions

On the Proton Conductivity of Nafion-Faujasite Composite Membranes for Low Temperature Direct Methanol Fuel Cells.

Although zeolites are introduced to decrease methanol crossover of Nafion membranes for direct methanol fuel cells (DMFCs), little is known about the effect of their intrinsic properties and the interaction with the ionomer. In this work, Nafion-Faujasite composite membranes prepared by solution casting were characterized by extensive physicochemical and electrochemical techniques. Faujasite was found to undergo severe dealumination during the membrane activation, but its structure remained intact. The zeolite interacts with Nafion probably through hydrogen bonding between Si-OH and SO3H groups, which combined with the increase of the water uptake and the water mobility, and the addition of a less conductive phase (the zeolite) leads to an optimum proton conductivity between 0.98 and 2 wt% of zeolite. Hot pressing the membranes before their assembling with the electrodes enhanced the DMFC performance by reducing the methanol crossover and the serial resistance

A covalent organic/inorganic hybrid proton exchange polymeric membrane: synthesis and characterization

Commercial polyetheretherketone (Victrex PEEK) was sulfonated up to 90% degree of sulfonation (DS), then reacted with SiCl4 to obtain a hybrid polymer. The product was characterized by 29-Si NMR and ATR/FTIR spectroscopies demonstrating the formation of covalent bonds between the organic and inorganic components. No dispersed inorganic silicon was present in the product as evidenced by the lack of any resonance at 100 ppm. Despite the high DS the physicochemical properties of the hybrid were suitable for the preparation of membranes exhibiting high and stable conductivity values (10K2 S/cm), hence suitable for application as ion exchange membrane