Fuel cells have the potential to become an important energy conversion technology. Research efforts directed toward the widespread commercialization of fuel cells have accelerated in light of ongoing efforts to develop a hydrogen-based energy economy to reduce dependence on foreign oil and decrease pollution. Proton exchange membrane (also termed “polymer electrolyte membrane”) (PEM) fuel cells employing a solid polymer electrolyte to separate the fuel from the oxidant were first deployed in the Gemini space program in the early 1960s using cells that were extremely expensive and had short lifetimes due to the oxidative degradation of their sulfonated polystyrene-divinylbenzene copolymer membranes. These cells were considered too costly and short-lived for real-world applications. The commercialization of Nafion by DuPont in the late 1960s helped to demonstrate the potential interest in terrestrial applications for fuel cells, although its major focus was in chloroalkali processes. PEM fuel cells are being developed for three main applications: automotive, stationary, and portable power. Each of these applications has its unique operating conditions and material requirements. Common themes critical to all high performance proton exchange membranes include (1) high protonic conductivity, (2) low electronic conductivity, (3) low permeability to fuel and oxidant, (4) low water transport through diffusion and electro-osmosis, (5) oxidative and hydrolytic stability, (6) good mechanical properties in both the dry and hydrated states, (7) cost, and (8) capability for fabrication into membrane electrode assemblies (MEAs). Nearly all existing membrane materials for PEM fuel cells rely on absorbed water and its interaction with acid groups to produce protonic conductivity. Due to the large fraction of absorbed water in the membrane, both mechanical properties and water transport become key issues. Devising systems that can conduct protons with little or no water is perhaps the greatest challenge for new membrane materials. Specifically, for automotive applications the U.S. Department of Energy has currently established a guideline of 120 °C and 50% relative humidity as target operating conditions, and a goal of 0.1 S/cm for the protonic conductivity of the membrane. New membranes that have significantly reduced methanol permeability and water transport (through diffusion and electro-osmotic drag) are required for portable power oriented direct methanol fuel cells (DMFCs), where a liquid methanol fuel highly diluted in water is used at generally <90 °C as the source of protons. Unreacted methanol at the anode can diffuse through the membrane and react at the cathode, lowering the voltage efficiency of the cell and reducing the system’s fuel efficiency. The methanol is usually delivered to the anode as a dilute, for example, 1 M (or less), solution (3.2 wt %), and relatively thick Nafion 117 (1100 EW, 7 mil ∼ 178 μm thick) is used to reduce methanol crossover. The dilute methanol feed increases the system’s complexity and reduces the energy density of the fuel, while the thick Nafion membrane increases the resistive losses of the cell, especially when compared to the thinner membranes that are used in hydrogen/air systems. The presence of excessive amounts of water at the cathode through diffusion and electro-osmosis * To whom correspondence should be addressed. E-mail: jmcgrath@vt.edu. † Sandia National Laboratory. ‡ Case Western Reserve University. § Los Alamos National Laboratory. | Virginia Polytechnic Institute and State University. 4587 Chem. Rev. 2004, 104, 4587−4612

Alternative Polymer Systems for Proton Exchange Membranes (PEMs)

Synthesis and characterization of sulfonated poly(ether ether ketone) for proton exchange membranes

Polymeric membrane pervaporation

Collagen, particularly atelopeptide collagen, exhibits improved handling characteristics when chemically conjugated and/or crosslinked with a synthetic hydrophilic polymer.

Collagen-polymer conjugates

https://www.journalofprosthodonticresearch.com/article/S1883-1958(15)00099-7/pdf

Applications of polyetheretherketone (PEEK) in oral implantology and prosthodontics

Hydrophobic poly(ether ether ketone) (PEEK) were modified by sulfonation at different temperatures (22, 36, 45, and 55°C) and varying period of time with concentrated sulfuric acid used as solvent A kinetic study was carried out based on the assumption that sulfonation reaction is a second-order reaction, which takes place preferentially in the aromatic ring between the two ether (O) links (the first type substitution), and there is only one substituent attached to each repeat unit of the PEEK before the complete substitution of this preferred aromatic ring More than 100% substitution was observed in experiment All the data with substitution degree less than 95% agree fairly well with the kinetic behavior of the second-order reaction The reaction rate coefficient and activation energy for first type substitution were obtained The sulfonated PEEK samples were characterized in terms of ion-exchange capacity (IEC), 1H-NMR, contact angle, and solubility © 2001 John Wiley & Sons, Inc J Appl Polym Sci 82: 2651–2660, 2001

Sulfonation of poly(ether ether ketone)(PEEK): Kinetic study and characterization

Melange polycarbonate du bisphenol A/PMMA prepare par coulee d'une solution ou extrusion a vis

Blends of polycarbonate and poly(methyl methacrylate) and the determination of the polymer-polymer interaction parameter of the two polymers

Blends of bisphenol-A polycarbonate (PC) and polystyrene (PS) prepared by screw extrusion and solution casting have been investigated with weight fractions of PC in the blends varying from 0.95 to 0.05. From the measured glass transition temperatures (Tg) and specific heat increments (ΔCp) at the Tg, the polystyrene appears to dissolve more in the PC phase than does the PC in the PS phase. The blend appears to be near eqilibrium under extrusion conditions so that the polymer–polymer interaction parameter of PC/PS blends was calculated and found to be 0.038±0.004 for extruded blends at 250°C. Scanning electron microscopy supports the conclusion that the compatibility increases more in the region of PS-rich compositions than in the regions of PC-rich compositions of the PC/PS blends.

Thermal behavior, morphology, and the determination of the Flory–Huggins interaction parameter of polycarbonate–polystyrene blends

Poly(dimethyl siloxane) thin film composite membranes for propylene separation from nitrogen

A titration technique has been used to directly measure the proton uptake by ion-exchange poly(2-vinylpyridine) coatings as a function of solution pH. Contrary to the common assumption that each nitrogen in the pyridine ring is attached to an H+ when the polymer film is fully protonated, the use of the titration technique has shown that the portion of the pyridine sites actually protonated does not exceed 25% anywhere in the pH range where the coating is stable. The pKa value for the poly(2-vinylpyridine) coating has also been estimated to be 4.5 from the titration curve. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1493–1497, 2001

Charles M. Burns

Papers

Sulfonation of poly(ether ether ketone)(PEEK): Kinetic study and characterization

Blends of polycarbonate and poly(methyl methacrylate) and the determination of the polymer-polymer interaction parameter of the two polymers

Thermal behavior, morphology, and the determination of the Flory–Huggins interaction parameter of polycarbonate–polystyrene blends

Poly(dimethyl siloxane) thin film composite membranes for propylene separation from nitrogen

Proton uptake by poly(2-vinylpyridine) coatings