New directions in perfluoroalkyl sulfonic acid–based proton-exchange membranes
Not provided.
Chemistry↗
Engineering topics
Hamrock, Steven J.
Publications and source records attributed to Hamrock, Steven J..
Fuel cell subassemblies incorporating subgasketed thrifted membranes
An automated roll to roll method of making a fuel cell roll good subassembly is described wherein an elongated first subgasket web having a plurality of apertures is moved relative to a plurality of individual electrolyte membranes, each individual electrolyte membrane having a center region. The individual electrolyte membranes are aligned with the first subgasket web so that a center region of each electrolyte membrane is aligned with an aperture of the first subgasket web and the individual electrolyte membranes are attached to the first subgasket web.
30 DIRECT ENERGY CONVERSION↗
Heteropoly acid functionalized fluoroelastomer with outstanding chemical durability and performance for vehicular fuel cells
To further facilitate commercialization of automotive fuel cells, durability concerns need to be addressed. Currently the addition of a mechanical support in the membrane is able to adequately solve issues of mechanical degradation, but chemical degradation via oxygenated radical attack remains an unsolved challenge. Typical mitigation strategies use cerium or manganese species to serve as radical scavengers, but these ions are able to migrate in the membrane and even leach out of the system. The approach used in this paper is to covalently link and immobilize a heteropoly acid (HPA), more specifically 11-silicotungstic acid (HSiW11), a lacunary HPA of the Keggin structure to a fluoroelastomer, serving as both a radical decomposition catalyst and the proton conducting acid. This dual functionality allows for both high content of radical scavenging species and high ion-exchange capacity. An efficient three step, high yield (77%), commercially viable synthesis for this polymer is reported. The synthesis route for making this new heteropoly acid functionalized polymer is confirmed using infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA). The material exhibits clustering of the HSiW11 moieties, resulting in a poorly connected proton conducting phase when dry, but excellent conductivity is achieved at elevated humidities (0.298 S cm -1 at 80 °C and 95% RH). The proton conductivity shows an enhancement above 60 °C due to a softening of the polymer, as shown by DSC. Under an aggressive chemical accelerated stress test (AST), 90 °C, 30% RH, zero current, and pure O 2 , the PolyHPA losses only 0.05 V of open circuit voltage (OCV) after 500 h, greatly out performing any other material reported in the literature. For comparison, the Nafion® N211 fuel cell drops below 0.8 V after only 76 h under the same conditions. Finally, in fuel cell testing the PolyHPAs have outstanding chemical stability and also possess very low in situ high frequency resistance (HFR) leading to high performance (1.14 W cm -2 at 2 A cm -2 ), compared to 1.11 W cm -2 for the Nafion® N211 fuel cell at the same current. At 75 wt% HSiW11 loading, the fuel cell HFR showed a 22% decrease over N211.
30 DIRECT ENERGY CONVERSION↗
Vibrational Spectroscopy for the Determination of Ionizable Group Content in Ionomer Materials
An approach based on vibrational spectral measurements is described for determining the ionizable group content of ion conducting polymer membrane materials. Aimed at supporting the assessment of membrane stability and wear characteristics, performance is evaluated for attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, confocal Raman microscopy, and ATR FT-IR microscopy using perfluorinated ionomer membrane standards. One set of ionomer standards contained a sulfonic acid ionizable group and the other a sulfonyl imide group. The average number of backbone tetrafluoroethylene (TFE) units separating the ionizable-group containing side chains was in the range of 7.2–2.1 (sulfonic acid set) and 10.5–4.6 (sulfonyl imide set). A poly(tetrafluoroethylene) (PTFE) sample was included as a blank, representing the limit of zero ionizable group (and maximum TFE) content. Calibration relationships were derived from area-normalized vibrational spectra. For all three methods, calibration models applied to independent spectral measurements of samples predicted the ratio of backbone TFE groups to ionizable groups in the repeat unit ( m) with a standard error of ≤ ±0.3. The confocal Raman and ATR FT-IR microscopy techniques achieved ideal blank responses and the lowest prediction errors, down to m ± 0.1 at the 90% confidence level. With its relative simplicity, low sample size requirements, and potential for quantitative micron-scale spatial mapping of the ionizable group content within a membrane, the approach has application to advancing materials development, including exploratory synthesis, durability and wear assessment, and in situ studies of membrane process.
Korzeniewski, Carol↗
Synthesis and Characterization of Perfluorinated Anion Exchange Membranes
Anion exchange membranes (AEMs) are of high interest for a number of electrochemical device applications including fuel cells, electrolyzers, and flow batteries. Perfluorinated sulfonic acid polymers have been the standard polymer used in the much more established area of proton exchange membrane based devices due to specific advantageous attributes including chemical stability, high conductivity, high water mobility, and the ability to create high performance electrodes. These attributes would make for desirable AEMs, but synthesizing perfluorinated AEMs has been limited and has significant challenges. Here, we report our efforts to develop novel synthesis routes to sulfonamide-linked alkyl ammonium perfluorinated AEMs. We have demonstrated the ability to achieve both high levels of ion exchange and membrane conductivity. We have achieved improved durability by extending the length of the alkyl tether from 3 to 6 carbons, and we have demonstrated the ability to process these polymers into membranes, ionomer solutions/dispersions, and fuel cells with reasonable performance.
30 DIRECT ENERGY CONVERSION↗
Low equivalent weight polymers
Described herein is a composition comprising: a polymer derived from (a) a fluorinated olefin monomer; (b) a highly fluorinated sulfur-containing monomer of the formula: CX1X2═CX3[(CX4X5)w—O—R1—SO2Y] where X1, X2, X3, X4, and X5 are independently selected from H, Cl, or F; w is 0 or 1; R1 is a non-fluorinated or fluorinated alkylene group; and Y is selected from F, Cl, Br, I, or OM, where M is a cation; and (c) a polyfunctional monomer comprising at least two functional groups, wherein the functional groups are selected from the group consisting of: (i) a fluorovinyl ether group, (ii) a fluoroallyl ether group, (iii) a fluorinated olefinic group, and (iv) combinations thereof; articles thereof; and a method of making such polymers.
30 DIRECT ENERGY CONVERSION↗
Fuel cell electrodes with conduction networks
A fuel cell electrode layer may include a catalyst, an electronic conductor, and an ionic conductor. Within the electrode layer are a plurality of electronic conductor rich networks and a plurality of ionic conductor rich networks that are interspersed with the electronic conductor rich networks. A volume ratio of the ionic conductor to the electronic conductor is greater in the ionic conductor rich networks than in the electronic conductor rich networks. During operation of a fuel cell that includes the electrode layer, conduction of electrons occurs predominantly within the electronic conductor rich networks and conduction of ions occurs predominantly within the ionic conductor rich networks.
30 DIRECT ENERGY CONVERSION↗