Influence of the basic membrane properties of the disulfonated poly(arylene ether sulfone) copolymer membranes on the vanadium redox flow battery performance

This article focuses on structure-property-performance relationship of directly copolymerized disulfonated poly(arylene ether sulfone) membranes (BPSH) utilized in vanadium redox flow batteries (VRFBs). Degree of disulfonation was systematically altered from 25 to 45 M percent by introducing controlled amount of disulfonated monomer into the copolymer structure. For the first time with this study the relation has been established between VRFB cell performances and basic membrane properties such as ion exchange capacity (IEC), water uptake, proton conductivity, and vanadium (VO2+) permeability of BPSH membranes. BPSH with 25 M percent disulfonation (BPSH 25) showed delay time during discharging process due to the fluctuation of the discharging voltage caused by poor proton conductivity, 23 mS cm−1. Therefore, columbic efficiencies became greater than 100 percent for BPSH 25 indicating higher discharging time than charging time. On the other hand, the best performance in the series was observed with BPSH 35. Since it had almost three times higher proton conductivity than BPSH 25 and about 100 times lower vanadium permeability (1.6×10−13 m2 s−1) than BPSH 45. Although BPSH 45 had the highest proton conductivity (140 mS cm−1), its performance was deteriorated due to higher vanadium permeability (1.6×10−11 m2 s−1). It was also demonstrated that water uptake values of the series scales with the vanadium permeabilities. As a result, several basic membrane parameters were controlled and presented as tunable properties, which were function of VRFB performance.