Nanostructure, Water Adsorption Behavior and Conductivity of Proton‐Exchange Membranes Composed of Perfluorosulfonic‐Acid Ionomers With Long and Short Side‐Chains

ABSTRACT To obtain proton‐exchange membranes (PEMs) with improved performances, perfluorosulfonic‐acid (PFSA) ionomers with long side‐chains (LSC) and short side‐chains (SSC) are blended in the dispersion state and cast. All LSC/SSC blend membranes exhibit single and symmetrical α transition temperature ( T α ) peak and ionomer peak, evidencing the compatibility between LSC and SSC, especially in the wet state. With the increase of SSC mass fraction in blend membranes, the crystallinity is decreased, the sizes of crystalline and non‐crystalline hydrophobic domains, and the spacing between crystalline hydrophobic domains are all increased. The molecular structure, the hydrophobic and hydrophilic domains play a critical role in the water adsorption behavior of membranes. Meanwhile, the proton conductivity of blend PEMs is closely related to the density of sulfonic‐acid groups, the conformational interaction between the molecular chains of SSC and LSC, and the crystallinity of membranes. The synergistic mechanism between different PFSA ionomers is elucidated and the PEM with enhanced proton conductivity (1.06 times to SSC PEM and 1.40 times to LSC PEM) is obtained at the SSC/LSC mass ratio of 2/2.