Design and Optimization of a Hyper-Branched Polyimide Proton Exchange Membrane with Ultra-High Methanol-Permeation Resistivity for Direct Methanol Fuel Cells Applications

A hyper-branched sulfonated polyimide (s-PI) was synthesized successfully and composited with polyvinylidene fluoride (PVDF) to achieve ultra-high methanol-permeation resistive for direct methanol fuel cell application. The optimized s-PI-PVDF composite membrane exhibited methanol resistivity low to 1.80 × 10−8 cm2/s, two orders of magnitude lower than the value of the commercial Nafion 117 membrane (60 × 10−7 cm2/s). At the same time, the tensile strength of the composite membrane is 22 MPa, which is comparable to the value of the Nafion 117 membrane. Therefore, the composite membrane is promising for application in direct methanol fuel cell.