Improved vanadium barrier properties of perfluorinated sulfonic acid membranes for vanadium redox flow battery

Abstract

The search for highly vanadium selective membrane for vanadium redox flow battery (VRFB) is fast growing to accelerate the commercialization of VRFB. Currently, VRFB is challenged by high vanadium permeability through the membranes lowering the battery performance. In this paper, a simple and effective strategy for improving the vanadium barrier permeability of the membranes, without altering the desired proton conductivity, was reported by applying layer(s) of polyelectrolytes. A commercial perfluorinated sulfonic acid membrane, GN115 was modified by layer of positively charged poly(diallyldimethylammonium chloride) (PDDA) or consecutive layers of PDDA and negatively charged poly(sodium styrene sulfonate) (PSS). Upon surface modification, the membranes exhibited a reduced vanadium permeability with a slight decreased in proton conductivity values compared with the pristine GN115 and N117. As a result, higher coulombic efficiency was obtained in VRFB single cell with the modified membranes. This confirms that the addition of the polyelectrolyte layers can suppress the vanadium permeability of the membranes.