A systematic investigations on the effect of sulfonic acid additives for the fabrication of thermally stable sulfonated poly(arylene ether sulfone) (PAES) composites for proton exchange membranes fuel cell applications were carried out. A uniform microstructure containing different concentration (1, 5 and 10 vol.%) of aromatic sulfonic acid additives (aniline‐2‐sulfonic acid (ASA), 3‐aminobenzenesulfonic acid (ABSA) and 3‐amino‐4‐hydroxy‐benzenesulfonic acid (AHBSA)) and biphenol‐based disulfonated poly(arylene ether sulfone) copolymer (PAES) as the matrix were successfully prepared. Phase segregation of the additives with sizes ranging from 1 to 2 μm was confirmed using scanning electron microscopy (SEM). Both thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) confirmed that additive derived PAES were thermally stable up to 400 °C. Proton conductivity of ASA‐PAES membranes was found to increase gradually with ASA concentration. Among all membranes PAES‐10 %ASA exhibited the highest conductivity of 0.123±0.01 S⋅cm−1 at 100 % relative humidity. However, PAES‐1 %ASA and PAES‐10 %ABSA membranes demonstrated the lowest leaching. Water uptake, ion exchange capacity and leaching parameters were correlated to additive concentration. This study will serve as a guide for the fabrication of PAES membranes with high concentration of sulfonated group in the polymer chain with enhanced thermal stability and proton conductivity.

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