Proton exchange membranes with oriented ion channels for enhanced conductivity

The trade-off between proton conductivity and mechanical stability is a core challenge in designing high-performance proton exchange membranes (PEMs). Uniaxial stretching can improve the overall performance of the materials by creating ordered polymer structures. Currently, the effects of uniaxial stretching on the ordered structure, hydrophilic-hydrophobic phase interactions, and various properties of the membranes have not been fully explored. In this paper, PEMs with ordered structure were fabricated using uniaxial stretching technique, which oriented the ion channels, thus offering the membranes enhanced conductivity and mechanical properties simultaneously. The comprehensive investigation of the effects of stretching on internal structure, microphase separation, proton conductivity, mechanical properties, and gas barrier of the membranes was conducted, while the intrinsic mechanisms behind the improved proton conductivity were explored. It was demonstrated that uniaxial stretching induced the ionic and inter-crystalline domains within the membranes to be oriented. The size and amount of hydrophilic domains were increased, and the connectivity of hydrophilic ion channels was then enhanced. Consequently, the proton conductivity of the stretched membrane was 1.25 times that of the pristine membrane. Molecular dynamics simulations validated these observations, providing theoretical underpinnings for the improved conductivity. Meanwhile, stretching facilitated the orderly arrangement of polymer chains, thereby increasing the crystallinity of the PEMs from 12.27 % to 18.95 %. These changes in the microstructure contributed to the improvement of macroscopic properties, e.g., the tensile strength and Young's modulus of the membranes increased by 40.65 % and 22.38 %, respectively. These findings provided valuable insights for the design and development of ordered PEMs.