“…A variety of AEM backbones have been studied and developed so far, such as polystyrene [ 22 , 23 ], poly-phenylene oxide (PPO) [ 24 , 25 ], polysulfone [ 26 ] or fluorinated polymers [ 27 , 28 , 29 ], poly-ethylene-co-tetrafluoroethylene (ETFE) [ 30 ], polyetherimide (PEI) [ 31 ], polyvinyl alcohol (PVA) [ 32 ], poly-ether-ether ketone [ 33 ], poly(arylene ether ketone) [ 34 ], and poly-carbazole [ 35 ]. As well, the most extensively investigated functional groups are: –NH 3 + , –RNH 2 + , –R 2 NH + , =R 2 N 2+ , –R 3 P + , –R 2 S + , quaternary ammonium salts (QA) [ 36 , 37 ], and tertiary amines (e.g., BTMA) [ 31 , 32 ].…”