Membrane/ionomer proton conductivity

Park HB, Shin HS, Lee YM, Rhim JW (2005) Atmealing effect of sulfonated polysulfone ionomer membranes on proton conductivity and methanol transport. J Membr Sd 247 103-110... 

Luan, Y., Zhang, Y., Zhang, H., Li, L., Li, H., Liu, Y, Anneahng effect of perfluorosul-fonated ionomer membranes on proton conductivity and methanol permeability. J. Appl. 

Asano, N., Aoki, M., Suzuki, S., Miyatake, K., Uchida, H. and Watanabe, M. 2006. Aliphatic/aromatic polyimide ionomers as a proton conductive membrane for fuel cell applications. Journal of the American Chemical Society 128 1762-1769. 

In the hydrated ionomer membrane, liquid-like water acts as the pore former, pore filler, and proton shuffle. The wafer disfribufion and the random network morphology of aqueous pafhways determine proton conduction at... 

For instance, the Dow experimental membrane and the recently introduced Hyflon Ion E83 membrane by Solvay-Solexis are "short side chain" (SSC) fluoropolymers, which exhibit increased water uptake, significantly enhanced proton conductivity, and better stability at T > 100°C due to higher glass transition temperatures in comparison to Nafion. The membrane morphology and the basic mechanisms of proton transport are, however, similar for all PFSA ionomers mentioned. The base polymer of Nation, depicted schematically in Figure 6.3, consists of a copolymer of tetrafluoro-ethylene, forming the backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers, terminated by sulfonic acid head groups. °... 

The built-in and operation stresses are the consequences of the large swelling and shrinkage of the ionomer membrane when it uptakes and loses water. This is frequently referred to as dimensional instability in the literature. Water in the PFSA membrane is an essential ingredient of its proton conduction behavior. Water affects the morphology13,14 of the ionic clusters (at nanoscale) which... 

Nation ionomers are produced by copolymerization of a perfluorinated vinyl ether comonomer with tetrafluoroethylene resulting in the chemical structure shown in Figure 8.25 [162,166], This polymer and other related polymers consist of perfluorinated, hydrophobic, backbones that give chemical stability to the material. The material also contains sulfonated, hydrophilic, side groups that make hydration possible in the acidic regions, and also allow the transport of protons at low temperatures, since the higher limit of temperature is determined by the humidification of the membrane, since water is a sine qua non for conduction [166], The material exhibits a proton conductivity of 0.1 S/cm at 80°C [162], The membrane performance is then based on the hydrophilic character of the sulfonic acid groups, which allow proton transport when hydrated while the hydrophobic... 

The function of a proton-conducting ionomer such as Nafion in the catalyst layer is to provide an ionic path for proton migration from the membrane to the reaction site at the catalyst surface. Therefore, the content of the proton-conducting ionomer in the catalyst layer will greatly influence the transport of protons to the catalyst sites. The impedance spectra of fuel cells with different Nafion loadings in the catalyst layers of both the cathode and the anode at OCV were compared by... 

MEA performance is mainly limited by ORR kinetics, as well as oxygen transport to the cathode catalyst. Another major loss is due to proton conduction, in both the membrane and the cathode catalyst layer (CL). Characterization of the ionic resistance of fuel cell electrodes helps provide important information on electrode structure optimization, and quantification of the ionomer degradation in the electrodes [23],... 

Limoges et al. looked at the HOR catalytic activities of a series of heteropolyacids (HPAs) containing Mo and V. The CD is too low (a few mA/cm ) for them to be used as stand-alone anode catalysts, although it should be pointed out that the HPA loading of the anode used in this study was one to two orders of magnitude lower on a molar basis than that of a typical Pt anode. However, HPAs have been shown to be promising proton-conductive membrane/ionomer tillers and effective catalysts for H2O2 decomposition. On this basis, they may eventually become a part of fuel cell electrodes. 

The electrolyte membrane presents critical materials issues such as high protonic conductivity over a wide relative humidity (RH) range, low electrical conductivity, low gas permeability, particularly for H2 and O2, and good mechanical properties under wet-dry and temperature cycles has stable chemical properties under fuel cell oxidation conditions and quick start-up capability even at subfreezing temperatures and is low cost. Polyperfluorosulfonic acid (PFSA) and derivatives are the current first-choice materials. A key challenge is to produce this material in very thin form to reduce ohmic losses and material cost. PFSA ionomer has low dimensional stability and swells in the presence of water. These properties lead to poor mechanical properties and crack growth. 

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