Membranes based on 3M's perfluoro imide acid (PFIA) ionomer have been studied using the open circuit voltage (OCV) hold accelerated stress test. For these samples, a decay in the OCV potential within the first 200 hours was observed along with an increase in cell resistance that rapidly grows near the end of life. A multi-membrane electrode assembly (MEA) technique was employed to study the origins of these phenomena. Effluent water collected at the beginning of life and later, during a recovery protocol, was analyzed using liquid chromatography -mass spectroscopy (LC-MS). A variety of small molecule fragments were detected that could be traced to the ionomer side chain. The center layer of a three-membrane MEA was separated at the end of life and analyzed by 19 F nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Peaks associated with the bis(sulfonyl)imide group of the PFIA ionomer were observed to have reduced in intensity and new peaks, assigned to a perfluorosulfonamide side chain, appeared. The combination of the fragments detected in the effluent water, along with the spectral changes in the membranes after aging, point to one or more degradation processes involving the PFIA ionomer side chain. This decomposition is likely analogous to reactions described for perfluorosulfonic acid (PFSA) ionomers but with new consequences owing to the greater number of potential fragments.

High-power electrodes in electrochemical technologies (e.g., fuel cells) typically require ultra-thin catalyst layers, which, especially when multiphase flow exists, exhibit mass-transport limitations. These have been mitigated through new backing layer structures and nontraditional removal of water out of the anode side of the cell for a new design and operation paradigm.

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New ionomers based on perfluoro bis(sulfonyl)imides have been made by 3M and show promise for use in fuel cell membranes and electrodes. These ionomers have exceptionally high proton conductivity that can result in improved performance especially at low relative humidities. Fundamental to the success of these ionomers is oxidative stability in the fuel cell operating environment. Accelerated open circuit voltage (OCV) hold tests have been used to evaluate the durability and chemical stability of perfluoro bis(sulfonyl)imide ionomers in both membrane and electrode applications. A multi-layer membrane technique was employed to recover degraded samples for FTIR analysis and effluent water was collected and analyzed using LC-MS. These experiments show evidence that the carbon-sulfur bonds in the imide group are subject to the same cleavage mechanism proposed for the traditional perfluoro sulfonic acid (PFSA) ionomers.

Perfluoroalkylsulfonic acid (PFSA) ionomer membranes degrade under accelerated testing conditions such as open circuit voltage (OCV). Fluoride release rate is commonly used for evaluating the membrane degradation rate; however, many proposed degradation mechanisms should result in the release of small molecule polymer fragments. Liquid chromatography/mass spectrometry (LC/MS) methods are well suited to analyze for these fragments and provide insight into the degradation reactions. Accelerated OCV durability tests were conducted on membrane electrode assemblies made with 3M Ionomer ™ or Nafion™ XL membranes. Effluent water was analyzed for fluoride, sulfate, and trifluoroacetic acid by ion chromatography (IC) and other polymer fragments by LC/MS. The detection of partially hydrogenated side chain fragments and long chain dicarboxylic acids suggest hydrogen atoms play a significant role in these reactions. The results of this study show the possibility that more than one reaction may occur at the tertiary fluoride on the polymer backbone. The presence of a tertiary fluoride on the backbone and side chain of the Nafion™ XL membranes allows for these reactions in more than one location on this polymer. Performance loss for the Nafion™ XL samples during these tests is consistent with adsorption of ionomer fragments on the catalyst surface.