Dumbbell‐Shaped, Block‐Graft Copolymer with Aligned Domains for High‐Performance Hydrocarbon Polymer Electrolyte Membranes

Given the environmental concerns surrounding fluoromaterials, the use of high‐cost perfluorinated sulfonic acids (PFSAs) in fuel cells and water electrolysis contradicts the pursuit of clean energy systems. Herein, we present a fluorine‐free dumbbell‐shaped block‐graft copolymer, derived from the cost‐effective triblock copolymer, poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS), for polymer electrolyte membranes (PEMs). This unique polymer shape led to the alignment of the hydrophobic‐hydrophilic domains along a preferred orientation, resulting in the construction of interconnected proton channels across the membrane. A bicontinuous network allowed efficient proton transport with reduced tortuosity, leading to an exceptional ionic conductivity (249 mS cm−1 at 80 °C and 90 % relative humidity (RH)), despite a low ion exchange capacity (IEC; 1.41). Furthermore, membrane electrode assembly (MEA) prepared with our membrane exhibited stable performance over a period of 150 h at 80 °C and 30 % RH. This study demonstrates a novel polymer structure design and highlights a promising outlook for hydrocarbon PEMs as alternatives to PFSAs. A dumbbell‐shaped hydrocarbon block‐graft copolymer was synthesized for use as a polymer electrolyte membrane. The introduction of comb‐type side chains resulted in a highly aligned morphology with enhanced microphase separation. The poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene)‐graft‐poly(styrene sulfonic acid) membrane achieved outstanding ion conductivity and maintained stable fuel cell performance for 150 h.