Cyclic voltammetry, electrochemical impedance spectroscopy and current distribution measurements are employed at single cells and a fuel cell stack to reveal the differences and interrelations of ammonia, nitrogen oxide and nitrogen dioxide. It is shown that both nitrogen oxides are adsorbed at the catalyst as NO. The adsorption of NO 2 is weaker and therefore leads to a lower and slower degradation. Moreover, all gases cause inhomogeneous stress of the MEA, which can lead to an accelerated degradation of the fuel cell. NH 3 shows a combined reaction by partly being adsorbed as a nitric oxide and partly reacting with the perfluorosulfonic acid groups of the ionomer. Within the framework of climate protection and the protection of the population against pollutants, electromobility is becoming increasingly important worldwide. Polymer-Electrolyte-Membrane Fuel cell technology (PEMFC) plays a key role since it includes high driving ranges with short refueling times. For a successful market introduction, however, costs must be further reduced and the durability of the systems must be further increased. In this context, it is known that several air pollutants lead to a short-term loss of power and reduce the durability of fuel cells in the long term.Nitrogen compounds are of special interest due to their high concentrations in urban traffic. Diesel vehicles are responsible for a majority of NO x -emissions in urban areas. But also a medium-sized vehicle with gasoline engine and three-way catalytic converter can easily emit 2 ppm NO 2 at 120 km/h. 1 For that reason and especially because of stricter legislation, there will be an increase of cars with SCR catalytic converters (selective catalytic reduction) to reduce NO x emissions in the future. Selective catalytic reduction generally names the reduction of NO x by NH 3 to water and N 2 by the help of a selective catalyst. This technique has been used in combustion plants for several years. For more than 10 years, SCR-systems for passenger cars are in use as standard-production application. In vehicles, the NH 3 for the reduction is converted out of urea stored in an extra tank. The SCR-system is an effective way to reduce NO x in the vehicle exhaust. On the one hand, only the use of SCR methods currently enables compliance with the Euro 6 and Tier 2 Bin 5 standards for NO x . On the other hand, it was shown that there is significant NH 3 slippage during the SCR-process in vehicles.2 To ensure a nearly complete conversion of NO x to N 2 the dosing of NH 3 has to be hyperstoichiometric. Furthermore, the reaction is extremely temperature sensitive. This will increase NH 3 emissions in traffic over the next few years. The three nitric components are therefore of special importance in urban areas and for this reason, it is important to examine the negative influence of these compounds on PEMFC in detail.Several studies examine the influence of NO x on the cathode of PEMFCs. Most of them present a strong but reversible loss of power up to 60% because of 1 to 25 ppm NOx.3-9...

It is known that traffic related air contaminants cause power loss, decreasing lifetime or a complete failure of proton exchange membrane fuel cell (PEMFC). Therefore, the present study aims for a better understanding and the development of a data basis for further decisions in dealing with air contaminants for automobile applications. The first section provides an overview of scientific literature about the influence of important air contaminants on proton exchange membrane fuel cells (PEMFC). The second section describes an extensive study of air contaminants at possible automotive operating conditions using a full factorial matrix test. The specific variation of temperature, cell potential and harmful gas concentration resulted in 27 operating points for each used air contaminant. The gases NO, NO2, SO2, NH3, toluene and ethane were used. The results indicate significant degradation but as well the possibility of regeneration. The degradation caused by different harmful gases is both, dependent on temperature and potential. Furthermore, a clear difference of the influence of NO and NO2 at low concentrations could be shown. The experiments give an overview of the cathode harming potential of relevant air contaminants. Hence, the work provides a basis for the development of cathode air filter and regeneration techniques for automotive applications.

An experimental radar at 94 GHz has been developed, which is capable of delivering an instantaneous bandwidth of 4 GHz. The radar uses an FM-CW waveform and is fully solid state. The data undergo an ISAR imaging process to derive high resolution scattering centre distributions for targets measured in tower/turnlable configuration. The high resolution processing has to rely on an appropriate polar reformatting procedure, which is not necessary for ISAR imaging at millimetre waves with resolutions worse than 10 cm

Design considerationsand performance characteristics of a 150 MW pulsed klystron amplifier at S-Band are described. One of the main problems encoun-