Partially Fluorinated Sulfonated Poly(ether amide) Fuel Cell Membranes: Influence of Chemical Structure on Membrane Properties

Abstract

A series of fluorinated sulfonated poly (ether amide)s (SPAs) were synthesized for proton exchange membrane fuel cell applications. A polycondensation reaction of 4,4'-oxydianiline, 2-sulfoterephthalic acid monosodium salt, and tetrafluorophenylene dicarboxylic acids (terephthalic and isophthalic) or fluoroaliphatic dicarboxylic acids produced SPAs with sulfonation degrees of 80-90%. Controlling the feed ratio of the sulfonated and unsulfonated dicarboxylic acid monomers afforded random SPAs with ion exchange capacities between 1.7 and 2.2 meq/g and good solubility in polar aprotic solvents. Their structures were characterized using NMR and FT IR spectroscopies. Tough, flexible, and transparent films were obtained with dimethylsulfoxide using a solution casting method. Most SPA membranes with 90% sulfonation degree showed high proton conductivity (>100 mS/cm) at 80 °C and 100% relative humidity. Among them, two outstanding ionomers (ODA-STA-TPA-90 and ODA-STA-IPA-90) showed proton conductivity comparable to that of Nafion 117 between 40 and 80 °C. The influence of chemical structure on the membrane properties was systematically investigated by comparing the fluorinated polymers to their hydrogenated counterparts. The results suggest that the incorporation of fluorinated moieties in the polymer backbone of the membrane reduces water absorption. High molecular weight and the resulting physical entanglement of the polymers chains played a more important role in improving stability in water, however. OPEN ACCESSPolymers 2011, 3 223

Sulfonated Binaphthyl-Containing Poly(arylene ether ketone)s with Rigid Backbone and Excellent Film-Forming Capability for Proton Exchange Membranes

“…However, it suffers from several drawbacks such as severe fuel permeation and high cost [5]. Therefore, lots of works have been devoted to the development of alternative PEMs, including sulfonated polystyrenes [6,7,8], sulfonated poly(arylene ether)s [9,10,11,12], sulfonated poly(arylene thioether)s [13,14], sulfonated poly(ether amide)s [15], sulfonated polyimides [16,17], sulfonated polybenzimidazoles [18], and sulfonated poly(phthalazinone ether)s [19,20]. Among them, sulfonated poly(arylene ether)s have been widely researched because of their good film-forming capability, robust mechanical strength, high thermal stability, and tunable proton conductivity [3,5].…”

Fluorinated Polyamides

“…The instability of sulfonated aromatic PA toward hydrolysis and heat limits their fuel cell application [75,76]. Although fluorinated PAs have the potential to be used as a PEM, only a few examples of sulfonated aromatic PA PEMs have been reported.…”

“…Although fluorinated PAs have the potential to be used as a PEM, only a few examples of sulfonated aromatic PA PEMs have been reported. However, the reduced reactivity of fluorinated dicarboxylic acids in the polycondensation resulted in lower molecular weight fluorinated SPAs [75]. It was found that fluorine-containing polymers displayed improved processability, tensile properties, and oxidative and chemical stability [69,70].…”

“…The instability of sulfonated aromatic PA toward hydrolysis and heat limits their fuel cell application [75,76]. Bae's group has done some work on the sulfonated poly(ether amide)s [18,75]. However, the reduced reactivity of fluorinated dicarboxylic acids in the polycondensation resulted in lower molecular weight fluorinated SPAs [75].…”

Sulfonated aromatic copoly(ether–amide) membranes II

“…28 –30 Reported IEC values range from 1.37 meq/g for a polyamide structure containing the sulfonated diamine 2,4-diaminobenzenesulfonic acid (DABS) 31 to 2.22 meq/g for oxydianiline (ODA)-sulfoterephthalic acid monosodium salt (STA)-terephthalic acid (TPA)-90, poly(ether–amide) ionomers containing 4,4′-ODA, 2-STA, and TPA. 30 Sulfonated copolyaramides are known for their ability to absorb water, 24,27,30,32,33 which in turn could lead to higher proton conductivities. 30 Some copoly(ether–amide)s report high-performance conductivities that reach maximum values up to 165 mS/cm.…”