Study on Nafion/Nafion-g-poly (sulfobetaine methacrylate)-blended amphoteric membranes for vanadium redox flow battery

In order to reduce the vanadium ion permeability while still keep its high stability, atom radical polymerization (ATRP) method was used to introduce zwitterionic sulfobetaine methacrylate (SBMA) onto the Nafion matrix in homogenous solution. The Nafion-grafted poly SBMA (N-g-PSBMA) solution was then used to blend with common Nafion solution to prepare Nafion/Nafion-g-PSBMA (N/N-g-PSBMA) amphoteric membranes by solution casting method. The grafted resins and membranes were characterized by attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), energy dispersive X-Ray spectroscopy (EDX), scanning electron microscopy (SEM), and water-contact angle analysis. The results prove that the SBMA has been successfully grafted onto the Nafion backbones. Furthermore, the N/N-g-PSBMA membranes have shown higher ion selectivity, coulombic efficiency, and energy efficiency than that of pure recast Nafion (r-Nafion) membrane for VRB application. At the current density of 40-80 mA cm(-2), the average energy efficiency of the VRB with N/N-g-PSBMA-20% membrane has reached up to 84.9%, which is 4.2% higher than that of the VRB with the r-Nafion membrane at the same current densities. Moreover, the 100-cycles charge-discharge test proves that the N/N-g-PSBMA-20% membrane possesses higher stability and capacity retention ability than that of r-Nafion membrane, confirming the great potential of such membranes for VRB application.