Synthesis and proton conductivity of poly(styrene sulfonic acid)/heterocycle-based membranes

Abstract

Background: High proton conduction through anhydrous polymer electrolyte membranes is crucial for the application to chemical energy conversion devices such as fuel cells. In this context, novel proton conductors were produced by doping poly(styrene sulfonic acid) (PSSA) with 1H-1,2,4-triazole (Tri) and 1.12-diimidazol-2-y1-2,5,8,11-tetraoxadodecane (imi3), and their physicochemical properties were investigated. Results: Different polymer electrolyte membranes were produced by doping of PSSA with Tri and imi3. PSSATrix, and PSSAimi3x electrolytes were obtained where x is the doping ratio describing moles of Tri or imi3 per mole of -SO3H unit. The membranes demonstrated adequate thermal stability at least up to 200 °C and the dopants acted as plasticizers shifting the Tg values to lower temperatures. PSSATri1 has a maximum proton conductivity of 0.016 S cm-1 at 150°C and the proton conductivity of PSSAimi30.5 is approximately 10-4 S cm-1 at room temperature. Conclusions: Transparent, homogeneous and freestanding films of PSSATrix, and PSSAimi3x were produced. It was demonstrated that both Tri and imi3 are efficient proton solvents in PSSA host matrix, and they yielded promising defect-type conductivities compared to benzimidazole. Tri-doped membranes clearly showed better conductivity performance at higher temperatures (T > 100°C). Both PSSATrix and PSSAimi3x polymer electrolytes can be suggested for fuel cell applications. © 2007 Society of Chemical Industry.