Electrochemical properties of pore-filled anion exchange membranes and their ionic transport phenomena for vanadium redox flow battery applications

Anion exchange membranes (PE/VBC) are successfully synthesized by pore-filling a porous polyethylene (PE) substrate with poly(4-vinylbenzyl chloride) followed by amination with pyridyl functional groups for vanadium redox flow battery (VRFB) applications. The membrane crosslinked with 10% of DVB content (PE/VBC(10)), 33 μm in thickness, exhibits a low swelling ratio of 3.4% and a water uptake of 23%. In addition, the vanadium crossover rate of the PE/VBC(10) membrane is lower than Nafion 117 by 48% at a similar electrical area resistance. Electrochemical properties of the PE/VBC membranes are examined in terms of the transport number and migration of ions as well as the electrical area resistance. Transport numbers for anions of the PE/VBC(10) membranes are 0.96 and 0.97 in NaCl and NaOH solutions, respectively. In acidic solutions of HCl and H2SO4, the membrane shows remarkably higher cation transport numbers of 0.20 and 0.72, which imply that the membrane allows high proton permeation and it is advantageous in VRFB operations. Furthermore, the migration of ions reveals reasonably low fluxes of other cations through the anion exchange membrane. Finally, the energy efficiency of the PE/VBC (10) membrane is 90.2%, higher than Nafion 117 by 5.4%.