A novel self-assembled composite membrane, Nafion-[PDDA/ZrP]n with nacre-like nanostructures was
successfully fabricated by a layer-by-layer (LbL) method and used as proton exchange membrane for
vanadium redox flow battery applications. Poly(diallyldimethylammonium chloride) (PDDA) with positive
charges and zirconium phosphate (ZrP) nanosheets with negative charges can form ultra-thin nacrelike
nanostructure on the surface of Nafion membrane via the ionic crosslinking of tightly folded macromolecules.
The lamellar structure of ZrP nanosheets and Donnan exclusion effect of PDDA can greatly
decrease the vanadium ion permeability and improve the selectivity of proton conductivity. The fabricated
Nafion-[PDDA/ZrP]4 membrane shows two orders of magnitude lower vanadium ion permeability
(1.05 106 cm2 min1) and 12 times higher ion selectivity than those of pristine Nafion membrane at
room temperature. Consequently, the performance of vanadium redox flow batteries (VRFBs) assembled
with Nafion-[PDDA/ZrP]3 membrane achieved a highly coulombic efficiency (CE) and energy efficiency
(EE) together with a very slow self-discharge rate. When comparing with pristine Nafion VRFB, the CE
and EE values of Nafion-[PDDA/ZrP]3 VRFB are 10% and 7% higher at 30 mA cm2, respectively.