Design of Sandwich‐Structured SPEEK Based Composite Membranes With Enhanced Proton Conductivity and Dimensional Stability

ABSTRACT The inherent trade‐off between proton conductivity and dimensional stability severely limits the practical application of proton exchange membranes (PEMs). To address this issue, a unique sandwich‐structured membrane is presented. In this design, its outer surface layers form a rigid skeleton composed of polyimide (PI) nanofibers, which provide physical confinement and effectively suppress excessive water absorption and swelling. The middle functional layer is made up of an ethylenediamine‐modified graphene oxide (EGO)/sulfonated poly (ether ether ketone) (SPEEK) composite. Acid–base interactions between amino groups (‐NH 2 ) on EGO and sulfonic acid groups (SO 3 H) in SPEEK allow for the formation of continuous proton‐transport pathways. In contrast, this membrane achieves a high proton conductivity of 222.4 mS·cm −1 at 60°C and 100% RH, which is 9.3% higher than that of SPEEK, while area ratio (20.5%) and water uptake (64.6%) are reduced by 56.9% and 39.7%, respectively. The membrane maintains 91.4% of its initial conductivity after a 350‐h durability test at 60°C and 100% RH, which is still 26.9% greater than that of SPEEK. Overall, this sandwich‐structured approach offers an efficient path toward high‐performance PEMs by simultaneously improving proton conductivity and dimensional stability using synergistic physical confinement and interfacial chemical interactions.