Sulfonated NbS-based proton-exchange membranes for vanadium redox flow batteries.

In this work, novel proton-exchange membranes (PEMs) based on sulfonated poly(ether ether ketone) (SPEEK) and two-dimensional (2D) sulfonated niobium disulphide (S-NbS) nanoflakes are synthesized by a solution-casting method and used in vanadium redox flow batteries (VRFBs). The NbS nanoflakes are produced by liquid-phase exfoliation of their bulk counterpart and chemically functionalized with terminal sulfonate groups to improve dimensional and chemical stabilities, proton conductivity () and fuel barrier properties of the as-produced membranes. The addition of S-NbS nanoflakes to SPEEK decreases the vanadium ion permeability from 5.