Fluorene-containing cardo polymers as ion conductive membranes for fuel cells

For polymer electrolyte fuel cells, proton conducting electrolyte membranes are key materials. This review highlights aromatic polymers containing cardo groups and ionic functions as emerging electrolyte materials. First, the role of biphenyl fluorene groups on sulfonated polyimides is discussed. Discussion then focuses on how to balance proton conductivity and membrane stability with sulfonated poly(arylene ether)s making the most of the bulky cardo groups. Block copolymer structure containing fully sulfonated biphenyl fluorene groups in its hydrophilic component and compact hydrophobic component is proposed. Effect of superacid groups onto the properties of fluorene-containing polymers is discussed. Replacing sulfonic acid groups with ammonio groups afforded the cardo polymers highly anion conducting properties, which make them potentially applicable to alkaline fuel cells.