Non-perfluorinated membranes

In this sectiOTi the Protmi Exchange Membranes (PEM) used or with potential to be used in DAFC will be introduced. The ample spectra of PEM chemical structures, including perfluoiinated sulfraiic membranes, and non-perfluorinated membranes and their corresponding inorganic and organic composites or blends, will be addressed. 

The thermal stability of perfluorinated material is excellent as evidenced by the higher glass transition temperature over their respective non-fluorinated analogues (11). Accordingly, these perfluorinated materials can be used in electrochemical cells at an elevated temperature for better cell efficiency because of high conductivity and fast kinetics (12) The relatively high cost of the perfluorinated membrane limits its application in many electrochemical cells when cost-effectiveness is a major concern. 

Although the membranes used in some of the applications listed here are not of the perfluorinated variety, the chemical inertness, high electrical conductance and relatively high solute flux confer technical advantages over most non-fluorinated membranes. 

Peckham T J and Holdcroft S (2011), Structure-morphology-property relationships of non-perfluorinated proton conducting membranes , Adv Mater, 22, 4667 690. 

There is no doubt that the perfluorinated ionomer membranes take initiative in this field and contribute a great deal in the commercialization and wide diffusion of fuel cells in the early stage. In terms of environmental compatibility (recyclability or disposability) and production cost, the perfluorinated ionomer membranes should be replaced with non-fluorinated alternative materials within the next decade. Challenge is how to achieve comparable conductivity and durability with the non-fluorinated membranes. Currently, no alternative materials have overcome the trade-off relationship between these two conflicting properties. In addition to the... 

Chemical degradation of PFSA membranes seems to be accelerated by elevated temperature, OCV conditions, low relative humidity, and elevated gas pressures. The main mitigation is the addition of radical scavengers and removal of non-perfluorinated groups. Note, that the amount of metal scavenger ions added to the membrane is limited and does not affect much the conductivity. 

T.J. Peckham, S. Holdcroft, Structure-morphology-property reladonships of non-perfluorinated proton-conducting membranes, Adv. Mater., 22 (2010) 4667-4690. 

The development of perfluorinated membranes by DuPont during the 1960s has played a vital role in electrochemical system applications. The Nafion family or perfluorinated ionomer membranes meet the requirements for several electrochemical systems (chloroalkafine, fuel cells and some other non-fuel cell applications). A lifetime of over 60000 hours has... 

Perfluorinated membranes reinforced with woven PTFE, such as Nafion 324 or Nafion 417, are used in many industrial electrochemical processes. Unfortunately, the relatively coarse weave of the woven PTFE reinforcement results in membranes that are much too thick for high electrochemical performance. Some non-woven PTFE/perfluorinated ionomer composite membranes have been formulated for ion transport studies and for investigation of other properties relevant to chlor-alkaU and fuel cell applications. Advancements in materials and processing technology have resulted in the introduction of PTFE/perfluorinated ionomer composite membranes claimed by Gore and Associates, Inc. under the Gore Select trademark. Most types of ion exchange membranes contain some type of reinforcement because they are weak and tend to swell substantially as they incorporate a solvent onto their structure. This reinforcement can be a macro reinforcement or a micro reinforcement . 

Nation membranes (EW 1,100 g/mol) (la) are the most widely used and studied of all the perfluorinated PEMs. By comparison, little information is publicly available on structure-property relationships for non-Nation... 

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... 

Firstly, Nafion and other perfluorinated sulfonic acid ionomers will be discussed, along with inorganic- and organic-Nafion based composites. Secondly, we will introduce non-fluorinated single and composite membranes, including membranes for high temperature DAFC. Finally we will discuss anion conducting membranes for alkaline DAFC. 

Chlorine Section Chlorine blowers asbestos diaphragms, ion-exchange membranes (perfluorinated) TiorFRP... 

Membrane. Perfluorosulfonic acid (PFSA) is the most commonly used membrane material [4], PFSA membranes are relatively strong and stable in both oxidative and reductive environments, since the structure of PFSA is based on a PTFE backbone. The conductivity of a well-humidified PFSA membrane can be as high as 0.2s cm. As is well known, fuel cell operation at elevated temperatures can increase the rates of reaction, reduce problems related to catalyst poisoning, reduce the use of expensive catalysts, and minimize problems due to electrode flooding. Unfortunately, a PFSA membrane must be kept hydrated to retain its proton conductivity. Moreover, a PFSA membrane is alcohol permeable if it is used in DAFCs. Because of the disadvantages of PFSA membranes, many alternatives have been proposed [106]. Five categories of membranes are classified (1) perfluorinated, (2) partially fluorinated, (3) non-fluorinated, (4) non-fluorinated composite, and (5) others. 

Cai, Z., Liu, Y., Liu, S., Li, L., Zhang, Y., High performance of lithium-ion polymer battery based on non-aqueous lithiated perfluorinated sulfonic ion-exchange membranes. Energy Environ. Sci. 2012, 5 (2), 5690-5693. 

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