Fabrication and testing of a doped lanthanum gallate electrolyte thin-film solid oxide fuel cell

A supported lanthanum gallate (LSGM) electrolyte thin-film solid oxide fuel cell with Ni-YSZ cermet anode and strontium-doped lanthanum manganite (LSM)-yttria stabilized zirconia (YSZ) composite cathode was, for the first time, fabricated and tested. The cell was prepared by an unconventional approach, in which an LSGM thin film (about 15 mum thick) was first deposited on a porous substrate such as a porous YSZ disk by a wet process and sintered at a high temperature (above 1400degrees C). NiO was then incorporated into the porous substrate by a carefully controlled impregnation process and fired at a much lower temperature. In this way, the severe reaction between LSGM and NiO at a high temperature, which is required for the full densification of LSGM film, can be avoided. A strontium-doped LaMnO3 (LSM)-YSZ composite cathode was screen printed on the surface of the LSGM film and then fired at 1250degrees C. The electrolyte resistances of the SOFC single cells fabricated by this approach are much lower compared to those of thick LSGM film supported cells. A maximum output power density of over 0.85 W/cm(2) at 800degreesC with H-2 as fuel and air as oxidant for a fabricated cell was achieved. (C) 2002 The Electrochemical Society.

Preparation and characterization of palladium-based composite membranes by electroless plating and magnetron sputtering

Pd and Pd-Ag (24 wt.%) alloy composite membrane were prepared by electroless plating and magnetron sputtering, respectively. The membranes were characterized by scanning electron microscopy (SEM) and H-2 permeation measurement. Commercial microfiltration ceramic membrane were coated with gamma-Al2O3-based layer by the sol-gel method and used as substrate of Pd and Pd-Ag alloy film. Both the as-prepared membranes were shown: to be He gas-tight at room temperature with a thickness of <1 mu m. Permeation results showed that H-2 permeation through these composite membranes is mainly dominated by the surface chemistry of H-2 on or/and in the membranes. The membranes exhibited a high permeation rate of H-2 and a H-2/N-2 permselectivity of higher than 60 in the optimized operation conditions. (C) 2000 Elsevier Science B.V. All rights reserved.

Perovskite-type B-site Bi-doped ceramic membranes for oxygen separation

Novel mixed conducting oxides, B-site Bi-doped perovskites were exploited and synthesized. Cubic perovskite structures were formed for BaBi0.2COyFe0.8-yO3-delta (y less than or equal to 0.4) and BaBixCo0.2Fe0.8-xP3-delta (x=0.1-0.5) The materials exhibited considerable high oxygen permeability at high temperature. The oxygen permeation flux of BaBi0.2Co0.35Fe0.45O3-delta membrane reached about 0.77 x 10(-6) mol/cm(2) s under an air/helium oxygen partial pressure gradient at 900 degrees C, which was much higher than that of other bismuth-contained mixed conducting membranes. The permeation fluxes of the materials increased with the increase of cobalt content, but no apparent simple relationship was found with the bismuth content. The materials also demonstrated excellent reversibility of oxygen adsorption and desorption. Stable time-related oxygen permeation fluxes were found for BaBi0.2CO0.35Fe0.45O3-delta and BaBi0.3Co0.2Fe0.5O3-delta a membranes at 875 degrees C.

Titanium-based perovskite-type mixed conducting ceramic membranes for oxygen permeation

A titanium-based perovskite-type oxide was synthesized by an improved method of combining EDTA acid and citric acid complexes. High structural stability, good sintering ability, and relatively high oxygen permeation flux were obtained simultaneously for disks synthesized from this ceramic oxide. (C) 2002 Elsevier Science B.V All rights reserved.

Mesoporous spinel MgAl2O4 prepared by in situ modification of boehmite sol particle surface: I Synthesis and characterization of the unsupported membranes

Mesoporous spinel membranes as ultrafiltration membranes were prepared through a novel sol-gel technique. By in situ modification of the sol particle surface during the sol-gel process, control of the material structure on a nanometer scale from the earliest stages of processing was realized. Nano-particles with a chocolate-nut-like morphology, i.e. spinel MgAl2O4 as a shell and gamma -Al2O3 as a core, were first revealed by HRTEM results. The formation of the spinel phase was confirmed by X-ray diffraction (XRD). N-2 adsorption-desorption results showed that the mesoporous membranes had a narrow pore size distribution. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis of NaA zeolite membranes from clear solution

NaA zeolite membranes were successfully synthesized on a porous alpha -Al2O3 support from clear solution. The synthesis parameters, such as surface seeding, synthesis time, synthesis stages, etc. were investigated. Surface seeding can not only accelerate the formation of NaA zeolite on the support surface, but can also inhibit the transformation of NaA zeolite into other types of zeolites. A continuous NaA zeolite membrane formed on the seeded support after 2 h of synthesis. Gas permeation results showed that a synthesis time of 3 h produced the best NaA zeolite membrane. When the synthesis time was longer than 4 h, the NaA zeolite on the support surface began to transform into other types of zeolites, and the quality of the NaA zeolite membrane decreased. The quality of the NaA zeolite membrane can be improved by employing the multi-stage synthesis method. The NaA zeolite membrane with a synthesis time of 2 h after a two-stage synthesis showed the best gas permeation performance. The permeances of H-2, O-2, N-2, and n-C4H10 decreased as the molecular kinetic diameter of the gases increased. which showed the molecular sieving effect of the NaA zeolite membrane. The permselectivities of H-2/n-C4H10 and O-2/N-2 were 19.1 and 1.8, respectively. These values are higher than the Knudsen diffusion ratios of 5.39 and 0.94. However, the permeation of n-C4H10 also indicated that the NaA zeolite membrane had certain defects with diameters larger than the pore size of NaA zeolite. A synthesis model was proposed to clarify the effect of surface seeding. (C) 2001 Elsevier Science B.V. All rights reserved.

Investigation of platinum utilization and morphology in catalyst layer of polymer electrolyte fuel cells

Platinum utilization in the gas-diffusion catalyst layer and thin-film catalyst layer is investigated. The morphology of PTFE and Nafion in a simulated catalyst layer is examined by scanning electronmicroscopy (SEM) and transmission electron microscopy (TEM). The results show that the platinum utilization of the thin-film catalyst layer containing only Pt/C and Nafion is 45.4%. The low utilization is attributed to the fact that the electron conduction of many catalyst particles is impaired by some thick Nafion layers or clumps. For the gas-diffusion (E-TEK) electrode, the platinum utilization is mainly affected by the proton conduction provided by Nafion. The blocking effect of PTFE on the active sites is not serious. When the electrode is sufficiently impregnated with Nafion by an immersion method, the platinum utilization can reach 77.8%. Transmission electron micrographs reveal that although some thick Nafion layers and clumps are observed in the Pt/C + Nafion layer, the distribution of Nafion in the catalyst layer is basically uniform. The melted PTFE disperses in the catalyst layer very uniformly. No large PTFE clumps or wide net-like structure is observed. The reactant gas may have to diffuse evenly in the catalyst layer. (C) 1999 Elsevier Science S.A. All rights reserved.