A two layer ultrafiltration alumina membrane was prepared by a sol-gel process using boehmite sol as precursor. The sol was prepared by hydrolysation of aluminium tri-sec-butoxide. Sol properties, such as viscosity as a function of concentration and acidity, were investigated by using capillary viscometry, transmission electron microscopy and laser scattering photometry etc. The viscosity increased with an increase in concentration and a decrease in pH, while the particle shape and size of the sol were mainly determined by pH. The membrane prepared by a dipping procedure was characterized by both scanning electron microscopy and transmission electron microscopy. The results showed that the membrane thickness and surface morphology were affected by the dipping time, the viscosity and the temperature.

Yttria stabilized zirconia (YSZ) polymeric sols were synthesized by controlled hydrolysis and condensation of zirconium tetra-n-propoxide. Yttrium nitrate was added before hydrolysis as the source of yttria. Acetylacetone was used as chelating ligand to modify the reaction rate of zirconium alkoxide. The dependence of YSZ sol formation as well as gelation time was investigated experimentally on the contents of acetylacetone, n-propanol (solvent) and water for hydrolysis. With a stable sol, YSZ membranes were prepared on porous α-alumina supports by a dip-coating process. The membranes were characterized by scanning electron microscopy and gas permeability testing. Unsupported YSZ membranes were also prepared with the same sol, and were investigated with isothermal nitrogen adsorption/desorption porosimetry and X-ray diffraction. The results show that YSZ membranes with nanosize pores were successfully prepared by the sol-gel technique with the polymeric sols.

Electrolyte films of samaria-doped ceria (SDC, Sm0.2Ce0.8O1.9) are fabricated onto porous NiO-SDC substrates by a screen printing technique. A cathode layer, consisting of Sm0.5Sr0.5CoO3 and 10 wt% SDC, is subsequently screen printed on the electrolyte to form a single cell, which is tested at temperatures from 400 to 600℃. When humidified (3% H2O) hydrogen or methane is used as fuel and stationary air as oxidant, the maximum power densities are 188 (or 78) and 397 (or 304) mW/cm2 at 500 and 600℃, respectively. Impedance analysis indicates that the performances of the solid oxide fuel cells (SOFCs) below 550℃ are determined primarily by the interfacial resistance, implying that the development of catalytically active electrode materials is critical to the successful development of high-performance SOFCs to be operated at temperatures below 600℃.

Anode-supported solid oxide fuel cells (SOFCs) based on gadolinia-doped ceria (GDC, Gd0.1Ce0.9O1.95) are fabricated by a simple and cost-effective dry-pressing process. With a composite anode consisting of NiO+35wt.% GDC and a composite cathode consisting of Sr0.5Sr0.5CoO3 (SSC) and 10 wt.% GDC, the cells are tested at temperatures from 400 to 6508℃. When humidified (3% H2O) hydrogen is used as fuel and stationary air as oxidant, the maximum power densities are 145 and 400mW/cm2 at 500 and 600℃, respectively. Impedance analysis indicates that the performances of the SOFCs are determined essentially by the interfacial resistances below 5508C. Further, while the anodic polarization resistances are negligible, the cathodic polarization resistances are significant, suggesting that development of new cathode materials is especially important to SOFCs to be operated at low temperatures.

The electrochemical properties of the interfaces between an Sm0.2Ce0.8O1.9 (samaria-doped ceria, SDC) electrolyte and porous composite cathodes consisting of Sm0.5Sr0.5CoO3 (SSC) and SDC have been investigated in anode-supported single cells at low temperatures (400-600℃). The bilayer structures of the SDC electrolyte films (25 Am thick) and the NiO-SDC anode supports were formed by co-pressing and subsequent co-firing at 1350℃ for 5h. The effect of composition, firing temperature, and microstructure of the composite cathodes on the electrochemical properties is systematically studied. Results indicate that the optimum firing temperature is about 950℃, whereas the optimum content of SDC electrolyte in the composite cathodes is about 30 wt.%. It is noted that the addition of the proper amount of SDC to SSC dramatically improved the catalytic properties of the interfaces; reducing the interfacial resistance by more than one order of magnitude compared with an SSC cathode without SDC.