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Alkaline stability of benzyl trimethylammonium (BTMA)-functionalized polyaromatic membranes was investigated by computational modeling and experimental methods. The barrier height of hydroxide initiated aryl-ether cleavage in the polymer backbone was computed to be 85.8 kJ/mol, a value lower than the nucleophilic substitution of the αcarbons on the benzylic position of BTMA cationic functional group, computed to be 90.8 kJ/mol. The barrier heights of aryl− aryl cleavage (polymer backbone) are 223.8−246.0 kJ/mol. The computational modeling study suggests that the facile aryl−ether cleavage is not only due to the electron deficiency of the aryl group but also due to the low bond dissociation energy arising from the ether substituent. Ex situ degradation studies using Fourier transform infrared (FTIR) and 1 H nuclear magnetic resonance (NMR) spectroscopy indicated that 61% of the aryl−ether groups degraded after 2 h of treatment in 0.5 M NaOH at 80 °C. BTMA cationic groups degraded slowly over 48 h under the same conditions. In situ degradation studies validate the calculated results: anion exchange membrane fuel cells and water electrolyzer using poly(arylene ether) membranes exhibit a catastrophic, premature failure during lifetime tests, while no sudden performance loss is observed with an ether-free poly(phenylene) membrane. Despite the gradual performance loss due to the degradation of BTMA cation functional group, the membrane electrode assembly using the poly(phenylene) membrane exhibited a lifetime of >2000 h in the alkaline water electrolyzer mode at 50 °C.

A major, unprecedented improvement in the durability of polymer electrolyte membrane fuel cells is obtained by tuning the properties of the interface between the catalyst and the ionomer by choosing the appropriate dispersing medium. While a fuel cell cathode prepared from aqueous dispersion showed 90 mV loss at 0.8 A cm(-2) after 30,000 potential cycles (0.6-1.0 V), a fuel cell cathode prepared from glycerol dispersion exhibited only 20 mV loss after 70,000 cycles. This minimum performance loss occurs even though there was an over 80% reduction of electrochemical surface area of the Pt catalyst. These findings indicate that a proper understanding and control of the catalyst-water-ionomer (three-phase) interfaces is even more important for maintaining fuel cell durability in typical electrodes than catalyst agglomeration, and this opens up a novel path for tailoring the functional properties of electrified interfaces.

High performance of SnP2O7-based intermediate temperature fuel cells was obtained with a quaternary ammonium-biphosphate ion-pair coordinated polymer electrolyte.

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Electrode structure within PEFCs, including the Pt-ionomer interface, is created while making electrodes from catalyst inks based on ionomer dispersed in solvent. The relationship between final electrode structure and processing conditions is poorly understood. We have varied the solvent used in cathode catalyst inks, and then subjected the resulting MEAs to hydrogen-air performance and durability testing. Specifically, cathodes cast from inks based on inonomer dispersions in water-propanol-isopropanol (W/P cathode) initially perform better than cathodes cast from glycerol-based dispersions (Gly cathode), but are far less durable. After 10,000 potential cycles from 0.60 V to 1.0 V in N2, the performance on air of the W/P cathode falls significantly below that of the Gly cathode. NMR and neutron scattering measurements of ionomer dispersions, as well as AFM and TEM data from cast ionomer films, offer insight into how the effect of solvent choice on the ionomer structure may impact durability.

The curing time, surface adhesion and water absorption characteristics of Sylgard 184 were modified through the addition of catalysts and fillers. Incorporation of small amounts of a platinum-based Karstedt catalyst greatly decreased curing time at room temperature, whereas the addition of talcum powder (talc), polytetrafluoroethylene (PTFE) and NaY zeolite fillers changed surface adhesion and functionality of Sylgard 184. Fourier-transform infrared spectroscopy (FT-IR), rheological and mechanical tests (tensile strength and hardness) were used to quantify the acceleration in the curing time. The surface adhesion was evaluated for aluminum and glass-like substrates using a 90° peel-off test. The interaction between fillers and Sylgard was studied by molecular dynamics simulations, which showed the interaction between NaY and Sylgard is This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/app.48530 greater than that for PTFE. Water absorption studies indicated that 10 wt% NaY added to Sylgard 184 helped to improve water absorption, whereas incorporation of talc had the opposite effect.

In order to meet the needs of constantly advancing technologies, fabricating materials with improved properties and predictable behavior has become vital. To that end, we have prepared polydimethylsiloxane (PDMS) polymer samples filled with carbon nanofibers (CFs) at 0, 0.5, 1.0, 2.0, and 4.0 CF loadings (w/w) to investigate and optimize the amount of filler needed for fabrication with improved mechanical properties. Samples were prepared using easy, cost-efficient mechanical mixing to combine the PDMS and CF filler and were then characterized by chemical (FTIR), mechanical (hardness and tension), and physical (swelling, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and coefficient of thermal expansion) analyses to determine the material properties. We found that hardness and thermal stability increased predictably, while the ultimate strength and toughness both decreased. Repeated tension caused the CF-filled PDMS samples to lose significant toughness with increasing CF loadings. The hardness and thermal degradation temperature with 4 wt.% CF loading in PDMS increased more than 40% and 25 °C, respectively, compared with the pristine PDMS sample. Additionally, dilatometer measurements showed a 20% decrease in the coefficient of thermal expansion (CTE) with a small amount of CF filler in PDMS. In this study, we were able to show the mechanical and thermal properties of PDMS can be tuned with good confidence using CFs.