Effects of different kinds of surfactants on Nafion membranes for all vanadium redox flow battery

To investigate the effects of different surfactants on the properties of Nafion membrane, recast Nafion membranes were prepared with cationic (tetramethylammonium bromide (TMAB)), anionic (sodium dodecyl sulfate (SDS)), and nonionic surfactants (Triton X-100 (TX-100)). The prepared composite membranes were analyzed by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), AFM, WXRD, and small-angle X-ray scattering (SAXS) to investigate the microstructure of the membrane. The properties of the composite membrane, including the water uptake, ion exchange capacity, proton conductivity, VO2+ permeability, water transport, as well as the single cell performance are evaluated in detail. Results show that both the physical and electrochemical properties of the surfactant-modified Nafion membranes were quite different from the unmodified recast Nafion (r-Nafion) membrane. Vanadium redox flow battery (VRB) single cell tests indicate that the nonionic modified Nafion membrane possesses the best comprehensive performances among the three surfactants modified and r-Nafion membranes. At current density of 40–80 mA cm−2, the average energy efficiency (EE) of the VRB with TX-100 Nafion membrane is 2.6 % higher than that of unmodified r-Nafion membrane, while the average EE of the VRB with TMAB/Nafion is 3.2 % lower than that of r-Nafion membrane. Another important effect of surfactants on the Nafion is the water transport behavior across the different membranes. TMAB can decrease the water transport across Nafion membrane, while the SDS and TX-100 can slightly increase the water transport across Nafion membrane.