Sulfonated polyimide nanofiber framework: Evaluation of intrinsic proton conductivity and application to composite membranes for fuel cells

A series of proton conductive nanofibers were fabricated by an electrospinning method from various sulfonated polyimides bearing different polymer structures, such as block, graft, and block/graft structures. Except for S-b-PI and S-bg-PI that showed low solubility in the appropriate solvent, the four types of SPIs gave uniaxially-aligned nanofibers along with the nanofibrous mat, which is applicable as nanofiber framework for the composite membranes. The intrinsic proton conductivities of the uniaxially-aligned nanofibers were evaluated to discuss the influence of polymer structures on proton conductivity of the nanofibers. In accord with the result of this study, the S-r-PI nanofiber was selected to fabricate nanofiber framework composite membrane by composing with S-bg-PI that shows high proton conductivity and low gas permeability. The nanofiber framework composite membrane showed good proton conductivity as well as improved gas barrier property and membrane stability. The nanofiber framework composite membrane has a high potential for achieving high proton conductivity, gas barrier property, and membrane stability for future fuel cell application.