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This paper presents an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements. Also discussed are some of the new materials, technologies, and research directions being pursued to try to meet the demanding performance and durability needs of the PEM fuel cell industry. [ABSTRACT FROM PUBLISHER]

This paper presents an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements. Also discussed are some of the new materials, technologies, and research directions being pursued to try to meet the demanding performance and durability needs of the PEM fuel cell industry. [ABSTRACT FROM AUTHOR]

Ionomers are important to electrode function in energy conversion devices, such as fuel cells and electrolyzers, as the catalyst‐binding nanometer‐thick films under confinement, which compromises mass transport of species. Mitigating confinement effects is necessary for improved performance of polymer electrolyte fuel cells. Studies on perfluorosulfonic acid (PFSA) ionomers provided insights into origins of transport resistances, but limited improvements by current strategies necessitate a need for alternative chemistries to enhance film function. This work investigates new ionomers based on sidechain modifications of PFSA to tune local acidity and structure. Their application‐relevant properties (hydration, thermal‐transition) and nanomorphology are systematically characterized using environmental ellipsometry and grazing‐incidence X‐ray scattering, respectively, to develop chemistry‐structure‐property relationships in thin‐film motif (≤100 nm). Introducing acid sites to sidechains improves hydration and nano‐phase‐separation but reduce chain mobility. Replacing the hydrophilic end‐groups with hydrophobic perfluoro‐groups enhances mobility but disrupts phase‐separation. Although modifying sidechain functional groups alters ionomer‐substrate interactions (Pt/C), chemistry has greater influence on structure‐properties. Proton conductivity correlates with hydration, regardless of chemistry. This work improves the fundamental understanding of chemistry‐function relationships of ionomers by providing a novel means to independently control their side‐chain vs. end‐group and observe resulting effects on interfacial properties to modulate electrode function in electrochemical technologies. [ABSTRACT FROM AUTHOR]

Although the peak power density of anion exchange membrane fuel cells (AEMFCs) has been raised from ˜0.1 to ˜1.4 W cm-2 over the last decade, a majority of AEMFCs reported in the literature have not been demonstrated to achieve consistently high performance and steady-state operation. Poly(olefin)-based AEMs with fluorine substitution on the aromatic comonomer show considerably higher dimensional stability compared to samples that do not contain fluorine. More importantly, fluorinated poly(olefin)-based AEMs exhibit high hydroxide conductivity without excessive hydration due to a new proposed mechanism where the fluorinated dipolar monomer facilitates increased hydroxide dissociation and transport. Using this new generation of AEMs, a stable, high-performance AEMFC is operated for 120 h. When the fuel cell configuration is subjected to a constant current density of 600 mA cm-2 under H2/O2 flow, the cell voltage declines only 11% (from 0.75 to 0.67 V) for the first 20 h during break-in and the cell voltage loss is low (0.2 mV h-1) over the subsequent 100 h of cell testing. The ease of synthesis, potential for low-cost commercialization, and remarkable ex situ properties and in situ performance of fluoropoly(olefin)-based AEM renders this material a benchmark membrane for practical AEMFC applications. [ABSTRACT FROM AUTHOR]

Three different perfluorinated type polymers as anion exchange membranes for electrochemical applications were studied. They have a sulfonamide linkage to a spacer methylene chain attached to a tri‐methyl ammonium cation, specifically using a three carbon spacer chain (PFAEM_H_C3), and methylated imide polymers with three (PFAEM_CH3_C3) and six carbon spacer chain (PFAEM_CH3_C6). There are significant number of zwitterionic side chains in the PFAEM_H_C3 polymer and very few in the PFAEM_CH3_C3 or the PFAEM_CH3_C6 polymer. They have similar halide conductivity, but the PFAEM_CH3_C6 showed highest OH− conductivity, 122 mS cm−1 at 80 °C and 95% RH. The larger spacer chain polymer, PFAEM_CH3_C6 has a higher water uptake value (λ = 9) compared to PFAEM_CH3_C3(λ = 7) at 60 °C and 95% RH in the Cl− form. Therefore, it has a larger domain spacing of 4.9 nm versus 4.1 nm from small angle X‐ray scattering data. The polymer was characterized by FTIR and DFT was used to fully assign the spectra. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 700–712 [ABSTRACT FROM AUTHOR]

An extensive SAXS investigation of the 3M perfluorinatedsulfonicacid ionomer was performed to investigate the morphological changesthat occur during and after annealing at temperatures above the Tα. The effect of film thickness in therange studied, 11–45 μm, was found to be negligible.These properties were studied as a function of equivalent weight from700 to 1100 and correlated with the water uptake as measured by dynamicvapor sorption. Isoscattering points were observed in dynamic annealingexperiments of the unboiled annealed films at q=0.023, 0.096 Å–1. On initial water uptake thesefilms also showed isoscattering points at q= 0.024,0.220 Å–1; q= 0.029, 0.223Å–1; and q= 0.030, 0.211Å–1at 50, 80, or 95 °C, respectively,indicating a decrease in the symmetry of the scattering objects inthese size regimes. Isoscattering points were absent in similar wateruptake experiment for the films after boiling. [ABSTRACT FROM AUTHOR]

Abstract: A perfluorosulfonic acid (PFSA) polymer with pendant side chain –O(CF2)4SO3H was doped with the heteropoly acids (HPAs), H3PW12O40 and H4SiW12O40. Infrared spectroscopy revealed a strong interaction between the HPA and the PFSA ionomer. Modes associated with the peripheral bonds of the HPA were shifted to lower wave numbers when doped into PFSA membranes. Small-angle X-ray scattering (SAXS) measurements showed the presence of large crystallites of HPA in the membrane with d spacings of ca. 10Å, close to the lattice spacing observed in bulk HPA crystals. Under wet conditions the HPA was more dispersed and constrained the size of the sulfonic acid clusters to 20Å at a 5wt% HPA doping level, the same as in the vacuum treated ionomer samples. Under conditions of minimum hydration the HPA decreased the E a for the self-diffusion of water from 27 to 15kJmol−1. The reverse trend was seen under 100% RH conditions. Proton conductivity measurements showed improved proton conductivity of the HPA doped PFSAs at a constant dew point of 80°C for all temperatures up to 120°C and at all relative hummidities up to 80%. The activation energy for proton conduction generally was lower than for the undoped materials at RH ≤80%. Significantly the E a was 1/2 that of the undoped material at RHs of 40 and 60%. A practical proton conductivity of 113mScm−1 was observed at 100°C and 80% RH. [Copyright &y& Elsevier]