Cathode contamination mechanism

The cathode contaminants sources and general mechanisms are described in chapter 2, and a more detailed discussion on mechanisms, experimental results, and mitigation is provided in chapter 3. 

Contamination modeling is an important aspect of fuel cell development. It is required to interpolate and extrapolate experimental results to expected conditions in real-world operation, as it is impractical to test all combinations of reactant concentrations and fuel cell operating conditions. Modeling also assists in the development and validation of hypothesized contamination mechanisms. Model development for the anode is more extensive than that for the cathode contamination. The majority of the modeling deals with the kinetic effects associated with adsorption of contaminant species on the cathode and anode catalysts. 

At the fuel cell cathode side, the prominent contaminants are NO (NO and NO2) and SO (SO2 and SO3). These mainly arise from electricity generation and fossil fuel combustions. NO, adsorb weakly on the Pt catalyst surface, and the contamination mechanism is mainly via the formation of NHJ, which... 

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. 

Ammonia (NHj) Hydrogen production process <1 ppm Same mechanism as for cathode contamination of ammonia Same as for cathode contamination of ammonia... 

Lea.dAnodes. A principal use for lead—calcium—tin alloys is lead anodes for electrowinning. The lead—calcium anodes form a hard, adherent lead dioxide layer during use, resist corrosion, and gready reduce lead contamination of the cathode. Anodes produced from cast lead—calcium (0.03—0.09 wt %) alloys have a tendency to warp owing to low mechanical strength and casting defects. 

Electrokinetic soil treatment is a commercially available in situ technology for the removal of metals and organic compounds. The application of direct current (DC) in a porous medium leads to two transport mechanisms electromigration and electro-osmosis. The combination of these two transport phenomena results in the movement of contaminant ions toward either the cathode or anode. Nonionic contaminants are transported by electro-osmosis alone. 

Mechanical action might involve such activities as abrasion, deformation, heat or flame cleaning, and electrocleaning, which involves direct current hydrogen scrubbing at the cathode. Metal-bearing wastes associated with these actions would be due to the metalbearing contamination removed in the process as well as any of the metal substrate removed. 

The samples of 1 to 2 mm cross-section were cut of the metal ingots by electrospark discharge method, the samples were then glass sealed so that the visible electrode surface was of 0.5 to 1 cm [6], The electrodes were treated on concentrated solutions of H2SO4 and H2O2 in order to remove mechanical and organic contaminants, repeatedly washed in distilled water and subjected to alternate anode and cathode polarization at the potential of = 1.6 h 0.0 V during 10-15 minutes. 

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