A newly developed method is presented which allows the characterization of the electrocatalytic properties of highly dispersed electrocatalysts in a true rotating disk electrode (RDE) configuration by attaching the catalyst powder on a glassy carbon electrode via a thin Nafion film. Complete utilization and high reproducibility of both the electrode preparation and the catalyst loading could be shown via voltammetry and CO stripping voltammetry. Furthermore, RDE mneasurements on the electro-oxidation of hydrogen on Pt/Vulcan showed that the effect of diffusion through the Nafion film can be avoided by proper electrode preparation. Therefore, the electrode kinetics for fuel cell relevant reactions under continuous flow conditions can be measured directly without mathematical modeling.

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The possibility of using dimethyl ether (DME) as a fuel in direct oxidation polymer-electrolyte-membrane (PEM) fuel cells is investigated. A mechanism for DME electro-oxidation is proposed based on the results of half-cell experiments using cyclic voltammetry combined with gas-chromatographic (GC) analyses of a single direct DME fuel cell. It is shown that, as a consequence of this mechanism, there is an additional overpotential at the anode of a direct DME fuel cell which is related to the initial adsorption step on the catalyst surface. DME is typically not oxidized at the cathode of a PEM fuel cell. This minimizes unwanted effects of fuel crossover, leading to improved fuel-cell efficiencies compared to direct methanol fuel cells, especially at low-tomedium current densities.

Water Column Imaging Multibeam Echosounder Systems (MBES) are effective and sensitive tools for investigating free gas (bubble) release and its rise through the water column. The main advantages of MBES are the detection range and lateral coverage in the water column and at the seafloor; furthermore, they are becoming increasingly available on research vessels worldwide. However, high noise levels and systematic artefacts due to side-lobe induced signal interference degrade MBES Water Column Images (WCIs) and hampered automated bubble detection and related gas seepage investigations. We present a new technique advancing automated detection of bubble streams and moving toward a quantitative gas-release assessment. It is shown that bubble streams can be detected reliably by their spatio-temporal behavior even when they are discontinuous in WCI data. Using assumptions about the bubble rising trajectories, bubble release spots at the seafloor can be traced even if the source location is obscured by acoustic noise or unwanted acoustic targets. A map with acoustic response and source locations of bubbles being released can be produced and serves as a starting point for more detailed quantitative analyses. The efficiency of the method has been assessed at a methane seep site in the Dutch North Sea. Multiple survey lines are merged to a detailed acoustic map of the area. Processed results are in good agreement with manual investigations of the WCI data as well as ROV-based video analysis.Active hydroacoustic systems are efficient tools for detecting and investigating free gas (bubble) seepage in lakes and oceans. Due to the strong change in acoustic impedance, gas bubbles are excellent acoustic targets that can be detected in sonar systems over a wide distance/water depth. Natural vents or seeps release erratic, cyclic or constant bubble streams that can be detected in acoustic water column data (e.g., echograms from single-beam echosounders) by their typical "flare" shape or as rising line when single bubbles/bubble clouds are ensonified. Acoustic surveys using single-beam or split-beam echosounders are nowadays a standard method for seep studies e

Characterization of High-Surface-Area Electrocatalysts Using a Rotating Disk Electrode Configuration.-The method allows the characterization of the electrocatalytic properties of highly dispersed electrocatalysts by attaching the catalyst powder on a glassy carbon electrode via a thin Nafion film. The electrode kinetics for fuel cell relevant reactions under continuous flow conditions can be measured directly without mathematical modeling. -(SCHMIDT, T. J.; GASTEIGER, H. A.; STAEB, G. D.; URBAN, P. M.; KOLB, D. M.; BEHM, R.