Nafion membranes hydrogen sulfates

The primary drawbacks of the Nafion membranes are poor conductivity at low relative humidities (and consequently at temperatures >100 C and ambient pressure) and large crossover of methanol in direct methanol fuel ceU (DMFC) applications. As a result, considerable efforts have been made in recent years to overcome these drawbacks. Peihaps the most widely employed approach is the addition of inorganic additives to Nafion m branes to yield organic/inorganic composite membranes. Three major types of inorganic additives that have been studied (zirconium phosphates, heteropolyadds, metal hydrogen sulfates and metal oxides) are reviewed in the following. 

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. 

Chapter 11 also includes the polymer inorganic membranes consisting of Nafion and zirconium phosphates, heteropolyacids, metal hydrogen sulfates and metal oxides. Moreover, this chapter includes the design of thin film electrodes for MFA. 

The three relationships apply to current densities up to 3000 A/m. The DAP assembly comprises a hydrogen depolarized anode and a Nafion 117 membrane the electrolytic compartments are limited by Nafion 324 and Selemion AAV ionexchange membranes. The relationships further apply to operating temperatures of 60 - 70 °C and to 13-18% caustic soda, 200-300 sodium sulfate, and 10% sulfuric acid. 

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