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

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.