No abstract

Hydroxide anion conducting solid polymer membranes, also termed anion exchange membranes, are becoming important materials for electrochemical technology, and activity in this field, spurred by renewed interest in alkaline fuel cells, is experiencing a resurgence. Solid polymer anion exchange membranes enable alkaline electrochemistry in devices such as fuel cells and electrolyzers and serve as a counterpoint to proton exchange membranes, of which there is a large body of literature. For their seeming importance, the details of transport in alkaline exchange membranes has not been explored thoroughly. In this work, a chloromethylated polymer with a polysulfone backbone was synthesized. 1 H NMR spectroscopy was performed to determine the chloromethyl content and its position on the polymer structure. The chloromethylated polymer was solution cast to form clear, creasable films, and subsequent soaking of these films in aqueous trimethylamine gave benzyltrimethylammonium groups. The resulting anion exchange membranes swell in water and show varying degrees of ionic conductivity depending on their ion exchange capacity. The water mobility in the anion exchange membranes was greater than in previously studied proton exchange membranes; however, the transport properties in these new materials were lower than what might have been expected from the water behavior. This comparison gives some insight as to future anion exchange membrane design objectives.

A series of poly(phenylene)-based polyelectrolytes were synthesized from 1,4-bis(2,4,5triphenylcyclopentadienone)benzene and 1,4-diethynylbenzene by Diels-Alder polymerization. Postsulfonation of this high molecular weight and thermochemically stable poly(phenylene) with chlorosulfonic acid resulted in homogeneous polyelectrolytes with controllable ion content (IEC ) 0.98-2.2 mequiv/g). Fuel cell relevant properties such as high proton conductivity (123 mS/cm), chemical/thermal stability, and film toughness suggest that this polyelectrolyte material shows promise as a potential candidate for polymer electrolyte membrane fuel cells. Physical properties of this material, such as water uptake, thermal stability, and proton conductivity, are reported with respect to ion exchange capacity and compared to Nafion and a series of sulfonated poly(ether sulfone)s.