Cross-linked poly(arylene ether ketone) membranes sulfonated on both backbone and pendant position for high proton conduction and low water uptake

► Cross-linked PAEK membranes sulfonated on both backbone and pendant position were prepared. ► Cross-linked PAEK membranes with DS above 120% exhibited higher proton conductivity than Nafion®117. ► Methanol permeability and water uptake were maintained still very low, compared to Nafion®117. ► Properties of membrane were correlated with ionic cluster dimension measured by SAXS.