Directly Copolymerized Disulfonated Poly(arylene ether sulfone) Membranes for Vanadium Redox Flow Batteries

For the first time with this study, membranes from directly copolymerized disulfonated poly(arylene ether sulfone) (BPSH 35) were utilized to replace NafionTM in vanadium redox flow batteries (VRFB). Direct copolymerization provided exact control of the degree of disulfonation on the chemical structure. BPSH 35 showed higher proton conductivity (75 mS cm-1), lower vanadium permeability (1.6x10-13 m2 s-1) and better selectivity (4.7x1013 S m-3 s) than N212. The water uptake values for N212 and BPSH 35 membranes were 28 and 40 % by weight, respectively. Higher proton conductivity and water uptake were observed due to the higher ion exchange capacity (IEC) values of BPSH35. In spite of high water uptake of BPSH35, it showed better resistance to vanadium permeation which was most probably because of the chemically bulky nature of the membrane. Moreover, higher columbic (98.9 %) and energy efficiencies (75.6-90.3 %) at the considered current densities than N212 were achieved. Consequently, BPSH 35 membranes were successfully demonstrated as an inexpensive energy efficient candidate for VRFB.