Highly porous and nanostructured SnO 2 thin-film gas sensors with Pt interdigitated electrodes have been fabricated via a combustion chemical vapor deposition process. The SnO 2 films were less than 1 µm thick and consisted of nanocrystallines smaller than 30 nm. At 300 °C, the as-prepared SnO 2 gas sensor showed a sensitivity of 1075 to 500 ppm ethanol vapor, and the corresponding response time and recovery time were 31 and 8 s, respectively. The extrapolated low detection limit appears to be below 1 ppm. Consequently, the as-fabricated sensor demonstrated significant improvements over those reported in the literature. These highly sensitive, fast-responding, and low-cost SnO 2 sensors could have many practical applications.

Dense La 0.8 Sr 0.2 MnO 3 ͑LSM͒ electrodes were patterned by photolithography and fabricated via pulsed-laser deposition on Y 2 O 3-stabalized ZrO 2 ͑YSZ͒ electrolytes. Impedance analysis shows that the interfacial polarization resistance decreases significantly as electrode thickness drops below a critical value, beyond which the top surface of the LSM becomes active for oxygen reduction. However, when the LSM electrodes become too thin, the in-plane sheet resistance of the LSM starts to limit the utilization of the electrodes along their length. Quantification of the characteristic thickness is important not only to intelligent design of practical mixed-conducting electrodes but also to electrode design for fundamental studies.

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Due to its excellent conductivity and catalytic activity toward oxygen reduction, silver has been used as cathode (or electrocatalyst), current collector, or electrical contact in low-temperature solid oxide fuel cells (SOFCs). Here we report our findings on the contamination of silver or a silver-containing cathode from the chromium oxide layer found on a Cr-containing interconnect. Silver wire was attached to a patterned La 0.8 Sr 0.2 MnO 3 cathode deposited onto a yttrium oxide-stabilized zirconium oxide substrate. The samples were placed inside a temperature-and atmosphere-controlled sample chamber filled with Cr-containing vapor. Raman spectra collected in situ from the sample surface revealed the formation of silver chromate, Ag 2 CrO 4 , on the silver surface at temperatures as low as 500°C. At 625°C, the Ag 2 CrO 4 was found to have vaporized and deposited across the LSM surface. In light of this contamination, special attention should be given to the selection of a metallic interconnect layer for an SOFC system that uses silver or a silver-containing cathode. Further, the use of in situ Raman spectroscopy as a powerful tool for probing and mapping new phase formation on electrode surfaces under fuel cell operating conditions is demonstrated.