William Rauch

Sm0.5Sr0.5CoO3 cathodes for low-temperature SOFCs

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 °C). The bilayer structures of the SDC electrolyte films (25 μm thick) and the NiO–SDC anode supports were formed by co-pressing and subsequent co-firing at 1350 °C for 5 h. 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 °C, 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.

Direct synthesis of silicon nanowires, silica nanospheres, and wire-like nanosphere agglomerates

Elevated temperature synthesis has been used to generate virtually defect free SiO2 sheathed crystalline silicon nanowires and silica (SiO2) nanospheres which can be agglomerated to wire-like configurations impregnated with crystalline silicon. The SiO2 passivated (sheathed) crystalline silicon nanowires, generated with a modified approach using a heated Si–SiO2 mix, with their axes parallel to 〈111〉 are found to be virtually defect free. Modifications to the system allow the simultaneous formation of SiO2 nanospheres (d∼10–30 nm) as virtually monodisperse gram quantity powders which form large surface area catalysts for the selective conversion of ethanol to acetaldehyde.

Functionally Graded Cathodes for Honeycomb Solid Oxide Fuel Cells

Functionally graded cathodes were fabricated by slurry coating process for honeycomb solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes. The cathodes are composed of strontium-doped lanthanum manganate (LSM), gadolinia-doped ceria, and La 0 . 6 Sr 0 . 4 Co 0 . 2 Fe 0 . 8 O 3 (LSCF). The LSM content was gradually decreased, while the LSCF content was gradually increased with the increasing distance away from the electolyte-electrode interface. Scanning electron microscopy investigation and electrochemical impedance spectroscopy measurements revealed that the electrochemical performance of the graded cathodes depends sensitively on the microstructures that were primarily determined by firing temperatures. The cathodes graded in composition show interfacial resistances about 10 times lower than traditional LSM-YSZ cathodes that have similar microstructures and thickness. The graded cathode fired at low temperature has an interfacial resistance as low as 0.47 Ω cm 2 at 750°C, which is very encouraging for developing honeycomb fuel cells operated below 800°C.

Development of a selective gas sensor utilizing a perm-selective zeolite membrane

Reported here is a novel sensor that utilizes a zeolite film to selectively limit gas exposure of the sensing surface. A unique amperometric sensor design based on a non-porous mixed conducting sensing electrode enables the formation of a continuous zeolite film covering the entire sensor surface. The sensor was tested in a variety of oxygen containing gases. The sensor without a zeolite film responded strongly to both oxygen and carbon dioxide at a bias of 1.8 V. In contrast, the sensor coated with a zeolite film showed a discernable, but diminished response to oxygen, and a more marked drop in response to CO2 indicating that the diffusion of oxygen through the zeolite film is preferential to that of CO2. The response of the zeolite coated sensor to a mixture of oxygen and carbon dioxide gases is attributed primarily to the oxygen content. Expanding this concept using a variety of different zeolite structures covering an array of sensors, complete analyses of complex gaseous mixtures could be performed in a very small device.