A coupled-layer ion-conducting membrane using composite ionomer and porous substrate for application to vanadium redox flow battery

Abstract

A thin ionomer layer composed of perfluorosulfonic acid (PFSA) polymer in composite with functionalized alkoxysilane (FAS) is prepared and coated onto one side of a porous polyethylene (PE) substrate for vanadium redox flow battery (VRFB) to produce a coupled-layer membrane. The approaches are: (1) suppression of permeation through membrane using additive component, (2) the use of thin ionomer layer for lowering the amount of costly PFSA, and (3) strengthening the thin ionomer layer by coating onto an inexpensive PE substrate. The membrane is easily prepared using automatic control coater. The observation of morphology and infrared spectroscopy at both sides of the coupled-layer membrane confirm the thin ionomer layer on only one side of the PE substrate, plus the addition of FAS helps achieve lower diffusion coefficient. After the unit cell cycling, the coupled-layer membrane shows the good cycling performance closing to Nafion 212 membrane level. Additionally, the morphology after cycling of the coupled layers between PFSA ionomer and PE substrate can remain the same as in initial state, indicating a stable combination from both layers. Based on the easy production and the good performance, the developed membrane can be readily adapted by membrane manufacturer for the wide application in VRFB. • A thin ionomer layer is coated on one side of porous polyethylene substrate. • The thin layer reduces amount of costly perfluorinated sulfonic acid ionomer. • VRFB cell performance was good by closing to that of Nafion 212 membrane. • Unchanged morphology between two layer was found after VRFB unit cell operation.