Hydrophilic Cross-Linked Aliphatic Hydrocarbon Diblock Copolymer as Proton Exchange Membrane for Fuel Cells

This study proposes a hydrophobic and hydrophilic aliphatic diblock copolymer wherein the hydrophobic block contains glycidyl methacrylate (GMA) units that are distanced by poly(acrylonitrile) (PAN) segments to fabricate a proton exchange membrane (PEM). This diblock copolymer also known as ionomer due to the hydrophilic block comprising 3-sulfopropyl methacrylate potassium salt (SPM) block. The diblock copolymer was synthesized in the one-pot atom transfer radical polymerization (ATRP) synthesis. Subsequently, the membrane was fabricated by means of solution casting in which an organic diamine, e.g., ethylene diamine (EDA), was introduced to crosslink the diblock copolymer chains via the addition of amine to the epoxide group of GMA. As a result, the PEM attained possesses dual continuous phases, in which the hydrophobic domains are either agglomerated or bridged by the EDA-derived crosslinks, whereas the hydrophilic domains constitute the primary proton conducting channels. The in-situ crosslinking hydrophobic block by using a hydrophilic cross-linker represents the merit aspect since it leads to both improved proton conductivity and dimensional stability in alcohol fuel. To characterize the above properties, Nafion^® 117 and random copolymer of P(AN-co-GMA-co-SPM) were used as control samples. The PEM with the optimized composition demonstrates slightly better fuel cell performance than Nafion 117. Lastly, this diblock ionomer is nonfluorinated and hence favors lowering down both material and environmental costs.