Contaminants derived from fuel cell system components such as structural materials, lubricants, greases, adhesives, sealants, and hoses have been shown to affect the performance and durability of fuel cell systems. Between July 2009 and September 2013, the National Renewable Energy Laboratory (NREL) led a team to study the effect of system contaminants on the performance of polymer electrolyte membrane fuel cells. The team, made up of industry (GM), universities (University of South Carolina, University of Hawaii, and Colorado School of Mines (CSM)), and a national laboratory partner (Los Alamos National Laboratory), screened about 60 balance of plant (BOP) materials. Knowledge of the material contamination potential of various system components can be used by the fuel cell industry in selecting appropriate BOP materials and in cost-benefit analyses. Our goal was to increase the understanding of fuel cell system contaminants and to help guide the implementation and, where necessary, development of system materials that will help enable fuel cell commercialization.

NREL and CSM also studied the effect of membrane degradation model compounds of commercial Nafion and 3M commercial perfluorosulfonic acid (PFSA) membranes. Such compounds are derived from PFSA membranes when exposed to certain peroxides and hydroxyl radicals.^1,2 Two compounds in particular, perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid (DA-Naf) and perfluoro(4-sulfonic butanoic) acid (DA-3M), arise along with HF as the main membrane degradation compounds of Nafion and a 3M commercial PFSA membrane, respectively.^3.4 These degradation products have been shown to adsorb on Pt-based electrocatalysts, leading to a loss in catalyst electrochemical surface area (ECA), oxygen reduction reaction (ORR) activity, or both.^5,6 Other model compounds were also studied to gain fundamental insight on the adsorption effects solely due to sulfonic acid functional group, the carboxylic acid functional group, as well as that of the fluorocarbon chain length.

Recently, NREL and 3M examined the effect of perfluoro imide acid (PFIA) ionomer degradation products on the ORR activity by performing a series of rotating disc electrode (RDE) experiments. PFIA is a new multi-acid side chain ionomer that 3M Fuel Cell Components Group is developing for fuel cell applications, with the goal of improved conductivity compared to Nafion when operated at dry conditions. During an accelerated stress test (open circuit voltage (OCV) hold), 3M reported that a PFIA-containing fuel cell showed a decay in the OCV in the first 200 h and then an increase in the membrane resistance for the remaining 600 h.⁷ It is suspected that the oxidative degradation of the PFIA polymer may be similar to that of the PFSA systems. Three model compounds were provided by 3M and systematically studied at NREL with respect to the effect of the potential PFIA degradation products on ORR activity.

This presentation will briefly summarize the past efforts related to contaminants derived from fuel cell system components, along with the interactive material screening data tool that was developed to archive the results from these studies and make them publicly available,⁸ as well as the RDE studies of PFSA and PFIA membrane degradation model compounds.

Acknowledgement:

This work was supported by the U.S. Department of Energy (USDOE), Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Office (FCTO) under Contract No. DE-AC36-08GO28308 with Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory. Model compounds were provided by 3M for this study.

References:

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