Arylphosphonic acid-functionalized polyelectrolytes as fuel cell membrane material

In comparison to sulfonated polymers, phosphonic acid-functionalized polyelectrolytes possess higher proton conductivity at elevated temperatures, improved chemical and thermal stabilities, much lower water swelling, decreased fuel permeability, and enhanced proton conductivities in low hydration states. Arylphosphonic acid-functionalized polymers have been produced by the copolymerization of arylphosphonated monomers, as well as by various polymer-analogous functionalization reactions on high performance polymer backbones. Among the latter, the catalytic arylphosphonation of brominated high-performance polymers, such as poly(ethers), poly(sulfones), and poly(ether-ketones) represents an attractive and versatile synthetic route to arylphosphonic polyelectrolytes for application in polyelectrolyte membrane fuel cells (PEMFC). This review summarizes available syntheses of arylphosphonic acid-functionalized polymers, the data on such materials' membrane performance, and introduces special polyelectrolyte blends and new ionomers developed to meet the demands made on PEMFC membranes.