▪ Abstract  Recently, a number of papers about direct oxidation of methane and hydrocarbon in solid oxide fuel cells (SOFC) at relatively low temperatures (about 700°C) have been published. Even though the conversion of almost dry CH4 at 1000°C on ceramic anodes was demonstrated more than 10 years ago, the reports about high-current densities for methane oxidation at such low temperatures are indeed surprising. Several papers indicate that a catalytic effect (due to the mixed ionic and electronic conductivity) of CeO2-x is partially responsible for this effect. However, this seems to contradict previous reports, and thus this issue deserves further analysis.

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At the performance of depth profiling by glow discharge optical emission spectroscopy (GD-OES) the intensities of optical emission lines of sample and sputter gas elements are measured in dependence on the time of sputtering. Radio-frequency (rf) sputtering extended the field of application to nonconducting samples including transparent layers. For transparent coatings in the thickness range up to some micrometers, oscillations of measured intensities were observed. This behavior is explained by a thin-film interference effect and discussed for three different materials, i.e., SiO2, TiO2, and BaTiO3. As a result, a new procedure for the determination of either layer thickness or refractive index from GD-OES depth profiles is presented. This effect has to be considered for quantitative GD-OES analysis as well.