Effect of Caprolactam and Sulfate System-Derived Contaminants on Catalyst Activity and PEMFC Performanc

Abstract

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, were chosen for this study include structural materials, elastomers for seals and (sub)gaskets, and assembly aids (adhesives, lubricants). Two types of low cost structural plastic materials – a polythlalamide and a polyamide – have been studied. The contaminants from the BOP structural material were leached out via an accelerated aging procedure. The leachates obtained from these plastics were a mixture of organics, inorganics, and ions. Organics that were identified in the leachate solutions via gas chromatography mass spectrometry (GCMS) include 1,8 Diazacyclotetradecane-2,7-dione (DCTDD), aniline, and caprolactam. These plastic materials also released anions: chloride, phosphate, nitrates, and sulfates. Of the organics, inorganics, and ions found in the leachate solution, caprolactam and sulfate were chosen for further study. These model compounds were introduced individually and as mixtures to a working fuel cell to determine their effect on fuel cells performance. 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 each model compound and mixtures of compounds. The preliminary in-situ results indicated that the organic compound caprolactam had a large negative effect on fuel cell performance and that the effect was not recoverable. On the other hand, infusion of sulfate into the fuel cell seemed to have no effect. The results also suggested that there is an interaction between caprolactam and sulfate. Ex-situ electrochemical measurements were also carried out to understand the impact of these individual and mixtures of compounds on the catalyst electrochemical surface area and the oxygen reduction reaction. The goal is to better understand the contamination mechanisms of specific species and their interaction with one another, leading to mitigation strategies. 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.