ABSTRACT
Fuel cell contamination is a serious issue, particularly for proton electrolyte membrane (PEM) fuel cell operation and applications. At the anode, the hydrogen fuel contains impurities, such as CO, H2S, NH3, organic sulfur carbon, and carbon-hydrogen compounds. These impurities originate primarily from hydrogen production processes, namely the reformation of hydrocarbons. For the cathode, at present the most practical and economical supply of oxygen is air. As a result, air quality directly impacts PEM fuel cell performance. The most common air pollutants are nitrogen oxides (NOx, including NO and NO2), sulfur oxides (SOx, including SO2 and SO3),
CONTENTS
6.1 Introduction ................................................................................................ 179 6.2 Oxygen Reduction Mechanism ............................................................... 181 6.3 Review of Oxygen Reduction Kinetic Models ....................................... 185 6.4 Cathode Contamination Model ............................................................... 186
6.4.1 Cathode Contamination Reaction Mechanism ......................... 186 6.4.2 Cathode Contamination Model ................................................... 187
6.5 Model Validation and Results Discussion.............................................. 192 6.5.1 Toluene Contamination Mechanism ........................................... 192 6.5.2 Experiment ...................................................................................... 193 6.5.3 Oxygen Concentration .................................................................. 193 6.5.4 ORR Parameters ............................................................................. 194 6.5.5 Modeling Results and Discussion ............................................... 196
6.6 Discussion of Other Cathode Contamination Models ......................... 202 6.7 Summary ..................................................................................................... 204 References ............................................................................................................. 205
carbon oxides (COx, including CO and CO2), ammonia, ozone, and volatile organic chemical (VOC) species (such as benzoic compounds) [1-3]. The major sources of these contaminants are automotive vehicle exhaust, industrial emissions, and agricultural activities. In an urban environment (e.g., Vancouver, Canada), the NOx level can be as high as 100 ppb, which could cause a voltage drop of approximately 25 mV in single fuel cell performance, as shown in Figure 6.1 [4]. In a battleeld, the SOx may be as high as 0.5 ppm, which could induce power failure in a fuel cell stack power supply [5].
