Direct perfluorosulfonic acid membranes

Moon GY, Rhim JW (2008) Self-assembly modification of perfluorosulfonic acid membranes for the application to direct meytahnol fuel cells. Macromol Res 16 524—531... 

Only in a couple of long-term experiments was seal degradation observed, and this might have been the consequence of an inappropriate materials selection. Silicone seals in direct contact with a perfluorosulfonic acid membrane suffer from degradation, at the anode as well as at the cathode [84]. The degradation is probably caused by acidic decomposition of the sealing material, leading to... 

Composite Perfluorosulfonic Acid Membranes for Direct Methanol Fuel Cells... 

Recent fuel-cell membrane research efforts have been focused on three areas [2] (1) membranes for hydrogen/air fuel cells that operate above 100 °C at low humidity conditions, (2) high proton conductivity and low methanol permeability membranes for direct methanol fuel cells and (3) low-cost alternatives to perfluorosulfonic acid membranes for both DMFCs and hydrogen/air fuel cells. 

L. Su, Perfluorosulfonic acid membranes treated by supercritical carbon dioxide method for direct methanol fuel cell application, J. Membr. ScL, 335 (2009) 118-125. 

The electrolyte is a perfluorosulfonic acid ionomer, commercially available under the trade name of Nafion . It is in the form of a membrane about 0.17 mm (0.007 in) thick, and the electrodes are bonded directly onto the surface. The elec trodes contain veiy finely divided platinum or platinum alloys supported on carbon powder or fibers. The bipolar plates are made of graphite or metal. 

This review will outline the materials requirements for advanced alternative proton exchange membranes for fuel cells, assess recent progress in this area, and provide directions for the development of next-generation materials. The focus will be on the synthesis of polymeric materials that have attached ion conducting groups. State-of-the-art Nation and its commercially available perfluorosulfonic acid relatives will initially be discussed. Other chain-growth co-... 

Kreuer et al. [25] investigated the membrane properties, including water sorption, transport (proton conductivity, electro-osmotic water drag and water diffusion), microstructure and viscoelasticity of the short-side-chain (SSC) perfluorosulfonic acid ionomers (PFSA, Dow 840 and Dow 1150) with different lEC-values. The data were compared to those for Nafion 117, and the implications for using such ionomers as separator materials in direct methanol and hydrogen fuel cells discussed. Tire major advantages of PFSA membranes were seen to be (i) a high proton conductivity. 

The catalyst ink usually includes catalyst, carbon powder, binder, and solvent. Sometimes, other additives are added to improve the dispersion of the components and stabilize the catalyst ink. The catalyst either covers the surface of the GDL or directly coats the surface of the membrane (catalyst coated membrane, CCM). The CL usually consists of (1) an ionic conductor such as perfluorosulfonate acid (PFSA) ionomer to provide a passage for protons to be transported in or out, (2) metal catalysts supported on a conducting matrix like carbon, to provide a means for electron conduction, and (3) a water-repelling agent such as polytetrafluoroethylene (PTFE) to provide sufficient porosity for the gaseous reactants to be transferred to catalyzed sites [5, 6]. Every individual factor must be optimized to provide the best overall performance of a CL. 

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. 

During operation of PEMFCs, fluoride ions, sulfate ions, and low molecular weight perfluorosulfonic acid are found in drain water. Direct gas mass spectroscopy of the cathode outlet gas indicated the formation of HE, H O, CO, SO, SO, H SO, and HjSOj in OCV durability tests (Teranishi et al. 2006). PFSA membranes contain no a-hyi"ogens, which are vulnerable to radical attacks, and hence the membranes would be stable against radical attacks (Mitov et al. 2005) if they have perfectly... 

This chapter reviews characteristics and performance of modified sulfonic acid-based membranes, particularly composite membranes including inorganic fillers and short-side chain perfluorosulfonic membranes for intermediate temperature applications. The characteristics of these systems for operation in direct alcohol fuel cells, in polymer membrane (PEM) electrolyser and automotive PEM fuel cells are analyzed. 

A rational analysis of filler effects on structural, proton transport properties and electrochemical characteristics of composite perfluorosulfonic membranes for Direct Methanol Fuel Cells (DMFCs) was reported [7]. It has been observed that a proper tailoring of the surface acid-base properties of the inorganic filler for application in composite Nafion membranes allows appropriate DMFC operation at high temperatures and with reduced pressures [7]. An increase in both strength and amount of acidic surface functional groups in the fillers would enhance the water retention inside the composite membranes through an electrostatic interaction, in the presence of humidification constraints, in the same way as for the adsorption of hydroxyl ions in solution [7]. 

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