Modification compositing Nafion polymer

We will return to the discussion on the relationship between structure and properties in Nafion and Nafion-based membranes in a next section. The modification of NafiOTi with inorganic and organic compounds has been investigated [3,9] in order to improve the performance of these perfluorinated membranes in DAFC by reducing the methanol crossover, while enhancing water retention and thermal stability. Next subsections are devoted to describe the different types of inor-ganic/Nafion composites and polymer/Nafion blends that have been reported in the literature in relation to its use as electrolytes in DAFC. 

The majority of solid proton-conducting membranes, most commonly used in contemporary fuel cell technology, are hydrated perfluorinated sulfonic acid ionomers. In recent years, enormous programs in membrane research have explored empirically how various modifications of the benchmark material, viz. Nafion, affect the physical membrane properties. The main modifications include (1) varying the hydrophobic/hydrophilic composition of the polymer, (2) controlling the grafting density and lengths of the sidechains,... 

Trogadas and Ramani summarized the modification of PEM membranes, including Nafion modified by zirconium phosphates, heteropolyacids, hydrogen sulfates, metal oxides, and silica. Membranes with sulfonated non-fluorinated backbones were also described. The base polymers polysulfone, poly(ether sulfone), poly(ether ether ketone), polybenzimidazole, and polyimide. Another interesting category is acid-base polymer blend membranes. This review also paid special attention to electrode designs based on catalyst particles bound by a hydrophobic poly-tetrafluoroethylene (PTFE) structure or hydrophilic Nafion, vacuum deposition, and electrodeposition method. Issues related to the MEA were presented. In then-study on composite membranes, the effects of particle sizes, cation sizes, number of protons, etc., of HPA were correlated with the fuel cell performance. To promote stability of the PTA within the membrane matrix, the investigators have employed PTA supported on metal oxides such as silicon dioxide as additives to Nafion. 

Membranes from Blends and Composites The modification of various proton-conducting polymers by blending or doping with inorganic particles has been reported. Several examples, with low methanol permeability (relative to Nafion), are described next. 

Nafion-based hybrid membranes are traditionally used electrolytes for both PEM fuel cell and DMFCs. " Besides Nafion, many composite engineering thermoplastic polymers based on poly(etheretherketone) (PEEK), polyvinyl alcohol (PVA), polysulfone, " polybenzimidazole (PBI), polyimide, and other organic-inorganic composite membranes have been employed as alternative membranes for both PEM fuel cells and DMFCs due to their lower cost, comparable conductivity, high mechanical and thermal stabilities, and easy modification as well. 

Modeling of polymer membrane structure through dynamics simulations is generally coupled with the water/proton-transfer properties. Yana et al. conducted molecular dynamics (MD) simulations of Krytox-Silica-Nafion composite membranes in comparison to the pure Nation. A 5 wt% of carboxylic acid terminated perfluoropolyether hybrid with silica (Krytox-Silica) in Nation composite polymer was used in the modification of a PEM in order to improve its efficiency at high operating temperatures. MD simulations were carried out in order to understand the microscopic properties of two systems, Krytox-Silica in Nation and pure... 

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