Covalently incorporating a cationic charged layer onto Nafion membrane by radiation-induced graft copolymerization to reduce vanadium ion crossover

Nafion membrane has been covalently functionalized with a cationic charged layer synthesized by radiation-induced graft copolymerization of N,N-dimethylaminoethylmethacrylate (DMAEMA) into Nafion substrate and subsequent protonation to reduce vanadium ion crossover for the application in vanadium redox flow battery (VRFB). The chemical composition and structure of the modified Nafion were characterized by microscopic Fourier transform infrared spectroscopy and thermogravimetric analysis. The grafting behavior was monitored by changing the experimental parameters including dose, dose rate and monomer concentration. The growth of cationic charged layer was studied by surface composition analysis of the membranes using X-ray photoelectron spectroscopy and atomic force microscope. The conductivity and permeability of vanadium ions of the obtained membranes with varying grafting yields were also measured. The functionalized Nafion membrane with a barrier layers displayed substantial resistance to permeability of vanadium ions accompanied by a relatively lower conductivity in comparison to that of the pristine Nafion membrane. The selectivity of the protonated Nafion-g-PDMAEMA membranes was higher than that of Nafion membrane, indicating the strategy is suitable for modifying Nafion membrane aiming at VRFB system. This work paves the way for the development of a new class of Nafion-based membranes for the application of VRFB.