Non-fluorinated membranes

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. 

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... 

Roziere, J. and Jones, D.J., Non-fluorinated polymer materials for proton exchange membrane fuel cells, Ann. Rev. Mater. Res., 33, 503, 2003. 

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. 

L. M. Madeira, S.P. Nunes, Performance and efficiency of a DM EC using non-fluorinated composite membranes operating at low/medium temperatures. Journal of Power Sources 140 (2005) 41 9. 

The vast catalogue of polymeric materials reviewed here included Nafion composite with inorganic and organic fillers, and non-fluorinated proton conducting membranes such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly (vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. Anion-exchange membranes are also discussed because of the facile electro-oxidation of alcohols in alkaline media and because of the minimizatirHi of alcohol crossover in alkaline direct alcohol fuel cells. 

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. 

Several non-fluorinated alternative polymers have been proposed for DAFC, mainly based on sulfonated ionomers with an aromatic or aliphatic hydrocarbon skeleton [7], Kim and Pivovar [4] have reported the number of DMFC alternative membranes papers appearing in open hterature for years 1994—2004, showing that polyarylenes, polyvinyl alcohols, grafted and block polystyrenes copolymers, and polyimides were among the most studies polymer electrolytes. In view of the dramatic increase in the number of publications since 2005 (see Fig. 6.1), the trends have changed, as shown in Table 6.1, which sununaiized the publications in open literature for the period 2005-2012, as compared to the previous period. 

An important aspect for the understanding of the transport properties of such polymers is the study of their structure, down to the molecular level. Especially in the absence of swelling phenomena, when the penetrant solubility in the perlluoropolymer matrix is relatively low, as is usually the case for non-fluorinated hydrocarbon vapours, the main factor which determines the transport properties is the Free Volume (FV). Knowledge of the free volume is therefore often of great importance for the understanding of the transport properties of dense membrane materials. 

Table 3.5 Comparative Gas Transport Properties of Fluorinated and Non-Fluorinated Polyimide Membranes at 25 °C and 5 atm Pressure...

---