Modulated Blending of Sulfonated Polyether Ether Ketone and Polystyrene‐Ethylene‐Butylene Styrene to Form a Stable Polymer Electrolyte in Proton Exchange Membrane Fuel Cells

Sulfonated polyether ether ketone (SPEEK) and sulfonated polystyrene–ethylene–butylene–styrene (SPSEBS) blend membranes were developed as fluorine‐free proton exchange membranes (PEMs) for fuel cell applications, with the aim of balancing proton conductivity and long‐term durability. Structural and morphological analyses confirmed good miscibility and uniform phase distribution at low SPSEBS loadings. Incorporation of SPSEBS improved membrane flexibility, toughness, and oxidative stability while maintaining adequate ion exchange capacity and hydration. Pristine SPEEK exhibited the highest proton conductivity (0.15 S cm −1 at 90°C), whereas the SPEEK/SPSEBS (98–2) blend showed more stable polarization behavior and superior voltage retention during durability testing. The enhanced performance of the blend is attributed to improved mechanical integrity, moderated swelling, and greater resistance to oxidative degradation. These results demonstrate that controlled incorporation of SPSEBS provides an effective strategy to develop durable SPEEK‐based PEMs for long‐term PEMFC operation.