Cathode contamination oxygen reduction mechanism

Currently, several air-side contamination models have been published in the literature, ranging from simple empirical and adsorption models to general kinetic models. These models have been applied to simulate and predict SO2, NO2, NH3, and toluene contamination. The kinetic model is a very general one based on the associative oxygen reduction mechanism. It takes into account contaminant reactions, such as surface adsorption, competitive adsorption, and electrochemical oxidation, and has the capability of simulating and predicting both transient and steady state cell performance. The model can be applied to other cathode contaminants, e.g., SO2 and NO2. 

The first step in the chemical degradation mechanism is the production of hydrogen peroxide, which may be produced as a by-product of the oxygen reduction reaction on the cathode, or may be produced chemically by crossover of either hydrogen or oxygen to the opposite electrode. The hydrogen peroxide reacts with metal ion contaminants (M"+) acting as Fenton s catalysts to produce very reactive hydroperoxy and peroxy radicals, as described by equation (1.35) and equation (1.36). 

The mechanism postulates the formation of nitrous acid (HNO2) and nitric acid (HNO3) by the reaction of NO with oxygen at the cathode under wet conditions. The simultaneous occurrence of the anodic and cathodic steps comprising reactions (5.6) and (5.8) above on the cathode create a mixed potential at the electrode that tends to reduce the cathode potential and retard the oxygen reduction reaction (5.9) [37,38]. The impact of NO contamination is shown in Pigure 5.2 and Eigure 5.3. 

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