Gas crossover is an unavoidable phenomenon in proton exchange fuel cell membranes. Nitrogen and oxygen from the cathode pass through the membrane to the anode, while hydrogen crosses from the anode to the cathode. The hydrogen crossover leads to a reduction in efficiency due to parasitic hydrogen consumption and mixed potentials on the cathode electrode. Furthermore it causes degradation effects and pinhole formation. Hence the hydrogen crossover represents a fundamental factor for the lifetime of a fuel cell and quantification of the crossover is a key factor for membrane qualification.In this article two in situ electrochemical techniques to evaluate the hydrogen crossover are described, cyclic voltammetry and potential step method. Both methods and the achieved results are compared to each other. Finally the potential step method is applied to evaluate the hydrogen crossover as a function of the anode pressure and the hydrogen permeability coefficients are determined.

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.

Understanding of the influence of traffic‐related nitrogen oxides on proton exchange membrane (PEM) fuel cells is essential to improve life time and durability of fuel cell vehicles. In a 3‐year work, both the damaging mechanisms and the influence of NOx on PEM fuel cells under real environmental and operating conditions became more comprehensible. It could be shown that even a low concentration level of 150 ppb NOx, which is often exceeded in traffic areas, causes considerable power losses. Furthermore, NO leads to significantly faster voltage drops compared to NO2, so typical NO peaks during rush hour traffic can reduce the fuel cell power. The concentration profile also has an influence on the degradation. The impact of NOx peaks is more negative compared to continuous NOx dosing when charging the fuel cell with the same total amount of NOx. It is possible to recover the fuel cell but it takes several hours depending on operating conditions and prior contamination level. To increase the recovery process the fuel cell has to be operated at a cathode potential below 0.3 V to reduce NOx and detach the contaminant from the platinum catalyst. A negative effect is the formation of NH4+, which is suspected to decompose the membrane in long term perspective.

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