Electric field processing to control the structure of poly(vinylidene fluoride) composite proton conducting membranes

A novel method is reported for controlling the structure of poly(vinylidene fluoride) (PVdF) composite proton conducting membranes. When proton conducting Nafion or zirconium phosphate sulfophenylenphosphonate (ZrPSPP) particles are dispersed in a mixed colloidal suspension with PVdF particles, the proton conducting particles selectively respond to an applied electric field. Under appropriate conditions, the proton conducting particles are induced to assemble into chains that rapidly grow to span the gap between electrodes as the electric field is applied. By removing the solvent and melting the PVdF phase while applying the electric field, composite membranes were formed that have field-induced structure. In comparison to randomly structured composites, the electric field-processed Nafion/PVdF or ZrPSPP/PVdF composite membranes showed improved proton conductivity, water sorption, selectivity for protons over methanol, and controlled surface area changes upon swelling with water. The transport and mechanical properties of the electric field-processed composite membranes suggest the potential for improved performance in direct methanol fuel cells.