Improving the redox flow battery performance of low-cost thin polyelectrolyte membranes by layer-by-layer surface assembly

Abstract

The search of new membranes for vanadium redox flow battery with low vanadium ions permeation rates, high ion conductivity, excellent proton conductivity, low area resistance, chemical stability, and low cost is on a soaring demand. In this work, a simple modification method is applied to improve the performance of commercially available low-cost membranes by applying several polyelectrolytes layers. Particularly, graphene-containing commercial perfluorinated sulfonic acid membrane of GN212C with a thickness of 33 μm is modified by introducing alternate layers of positively charged poly(diallyldimethylammonium chloride) and negatively charged poly(sodium styrene sulfonate). Microscopy and spectroscopy investigations indicate that the polyelectrolytes layers are successfully deposited on the membrane surface. The effects of the layer composition and number of bilayers are evaluated with regard to vanadium ion permeability, proton conductivity and battery performance. The modified membranes exhibit an improved vanadium (VO2+) barrier property, which enhances the VRFB single cell performance in terms of coulombic efficiency and energy efficiency compared to pristine GN212C and Nafion 117 membranes. The overall results suggest that the bi-ionically modified membrane is a potential candidate for application in flow battery despite its small thickness.