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  • 1995-1999  (4)
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  • 1
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A galvanic cell based upon the use of stabilized zirconia as solid oxygen ion conductor has been used to measure cathodic reduction currents at a porous platinum electrode in both nitrogen-oxygen gas mixtures with and without small amounts of NO (up to 5450 ppm). Adding small amounts of NO to the N2/O2 mixture induced a considerable cathodic current peak at the working electrode in the first moment after addition. After interruption of the NO exposure, the opposite effect, a high current pulse in anodic direction, was observed. The switching effect is reproducible and its magnitude depends on the concentrations of oxygen and nitrogen monoxide in the gas. As the main contribution to the current results from the reduction of the excess oxygen in the gas, it must be concluded that the presence of NO strongly affects the steady state, in particular the adsorbed oxygen at the electrode/electrolyte interface. These experimental results are interpreted in terms of a reversible change of the interface which may be due to a reconstruction of the platinum surface in the presence of NO and corresponding drastic change in the amount of adsorbed oxygen at the platinum surface.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics for the electrode reactions with oxygen and with NO and NO2 in the presence of oxygen has been studied for La0.8Sr0.2MnO3±δ-electrodes on stabilized zirconia (8 mol% Y2O3=YSZ) in the temperature range between 500°C and 900°C for oxygen partial pressures between 1 kPa and 20 kPa by means of electrochemical methods (impedance, I-U characteristics) and temperature programmed desorption (TPD). For oxygen reduction below 900°C a mechanism is proposed which describes the formation of peroxidic ions at the electrode surface and a subsequent rate-determining electron transfer at the three-phase-boundary. At temperatures below 650°C the electrode reaction between NO and NO2 is much faster than the oxygen reduction. The results for the NO2-reduction to NO can be explained by a two-step mechanism consisting of a fast one-electron transfer to adsorbed NO2 at the electrode surface and a subsequent rate-determining transfer of the second electron to NO2 at the three-phase-boundary.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Multi electrode amperometric sensors based on stabilized zirconia have been studied with respect to the simultaneous detection of oxygen and NO. Both gases are of particular interest in oxygen rich exhaust gases. With a setup consisting of two subsequent electrodes it was possible to separate the reduction of oxygen and the reduction of NO spatially. Hence the currents of the two electrodes are directly correlated with the oxygen and the NO concentrations. Combustible gases like CO are oxidized at the oxygen electrode, thus lowering the effective oxygen concentration in the cell. H2O and CO2 are partly reduced at the NO electrode. This effect strongly depends on the applied potential and may be eliminated by an appropriate selection of the working parameters. The results demonstrate the potential of such multi electrode cells to the simultaneous detection of several gas components.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of the oxygen exchange reaction and the reduction of NO at La0.8Sr0.2CoO3−, La0.8Sr0.2MnO3− and Ag-electrodes on stabilized zirconia (8mol% Y203=YSZ) has been studied by means of electrochemical methods (impedance, I-U characteristics). For La0.8Sr0.2CoO3 electrodes the oxygen exchange was found to proceed via the bulk of the electrode with a rate limiting oxygen exchange at the electrode surface. Electrodes based on La0.8Sr0.2MnO3 change their electrode characteristics with the applied potential. At low cathodic polarization the electrode reaction is limited to the three-phase boundary electrode/YSZ/gas. At high cathodic potentials oxygen vacancies are created and consequently additional oxygen is exchanged via the electrode bulk. Furthermore, a significant NO reduction was observed which indicate a reaction with the oxygen vacancies at the electrode surface. For Ag a rate limiting transport of oxygen atoms through the bulk of the electrode was found. As a consequence the oxygen concentration at the electrode surface remains nearly constant. In this context, the observed inactivity for the NO reduction of Ag-electrodes may be explained.
    Type of Medium: Electronic Resource
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