Modification blending Nafion polymer

Apart from the blend membranes, introducing an ultrathin vanadium-resistant layer on membrane support could be another choice. For example, a positively charged polymer layer such as polyethylenimine (PEI), polypyrole and polyaniline can be deposited on the surface of a Nafion membrane to increase the ion selectivity [20-22]. Even though the modification of Nafion is an effective way to improve its selectivity, the extremely high cost of the membrane matrix still limited its further application. 

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. 

Abstract There have been numerous studies on modifying DuPont s Nafion (a perfluorosulfonic acid polymer) in order to improve the performance of this membrane material in a direct methanol fuel cell. Modifications focused on making Nafion a better methanol barrier, without sacrificing proton conductivity, so that methanol crossover during fuel cell operation is minimized. In this chapter, a brief literature survey of such modifications is presented, along with recent experimental results (membrane properties and fuel cell performance curves) for (1) thick Nafion films, (2) Nafion blended with Teflon-FEP or Teflon-PFA, and (3) Nafion doped with polybenzimidazole. 

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. 

---