(Invited) Monopolar and Bipolar Membranes Based on Nanofiber Electrospinning

Abstract

Cation-exchange, anion-exchange, and bipolar membranes play crucial roles in a variety of electrochemical processes and devices, including chloralkali cells, electrodialysis separations for water purification, proton-exchange membrane and hydroxide-exchange membrane (alkaline) fuel cells, redox flow batteries, and processes for direct air capture of CO2. The incorporation of polymeric nanofibers into such membranes provides an attractive and tunable method of creating materials with new nano-morphologies and highly desirable properties.The impregnation of an ionomer solution into a pre-formed nonwoven porous mat of electrospun polymer fibers is a well-known method of making reinforced proton-exchange membranes. The use of simultaneous dual-fiber electrospinning or the electrospinning of polymer blends can be used to intermix/incorporate/co-locate dissimilar and incompatible polymers on the nanoscale. Although less studied in the literature, these methods offer many interesting possibilities for new membrane structures with targeted and unique transport and mechanical properties.In this review talk, the use of dual fiber and blended polymer fiber electrospinning for membrane fabrication will be presented for the following: (1) Nanofiber reinforced cation (proton) exchange membranes, (2) Electrospun NafionTM/PVDF dual fiber and single-fiber membranes for H2/Br2 redox flow batteries, (3) Composite anion exchange membranes, and (4) Bipolar membranes with a 3D nanofiber junction. Materials and methods for membrane fabrication will be described and the properties of the membranes will be discussed.