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Lower cost materials for stack hardware and system components help reduce the overall cost of the automotive and stationary fuel cell systems and make these competitive in the market. However, low-cost system component materials need to provide similar function, performance and durability. Intelligently selecting low cost materials for application in polymer electrolyte membrane fuel cell (PEMFC) systems requires understanding the potential adverse effects that system contaminants may have on the fuel cell performance and durability. There are many prospective balance of plant (BOP) materials that can be used in fuel cell systems. Families of material, based on input from OEMs, fuel cell system manufacturers and other attributes like cost, physical properties, have been studied. These include structural materials, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants). The contaminants from the BOP materials were leached out via an accelerated aging procedure. The leachates obtained from these plastics were a mixture of organics, inorganics, and ions. The sulfate anion was one of the anions identified in the leachates and was chosen as the model compound for further studies. Sulfate anions can also come from membrane degradation. Ex-situ electrochemical measurements were carried out to understand the impact of sulfate anion concentration on oxygen reduction reaction (ORR). The ORR scan rate and direction (low to high potential and vice versa) were studied to determine the effect of the initial state of the Pt surface on sulfate contamination. In-situ fuel cell experiments were also carried out. Sulfate anion was introduced to a working fuel cell to determine their effect on fuel cells performance. Our previous work showed that sulfate anion did not result in performance loss when it was infused into the cathode at 0.2 A/cm2. The cathode potential was greater than 0.8 V at this current density. It is postulated that sulfate contamination is potential dependent and that sulfate adsorption only occurs when Pt is in its metallic state. In the current study, the effect of potential on sulfate contamination will be studied by infusing sulfate into the cathode at several constant current densities. Several in-situ diagnostics such as infusion, cyclic voltammetry, electrochemical impedance spectroscopy, and I-V curves were carried out to better characterize the contaminant effects of sulfate anion. The goal is to better understand the contamination mechanisms of specific species so that mitigation strategies can be determined. The authors would like to acknowledge funding from the U.S. Department of Energy EERE Fuel Cell Technologies Office, under Contract No. AC36-08GO28308 with the National Renewable Energy Laboratory and collaborations with colleagues at GM. Structural plastic materials and leachates were provided by GM for this study. |
