Sulfonated polyimide membrane containing poly [bis (4-aminodiphenyl bissulfonate) phosphoronitrile] flexible chains for vanadium redox flow battery

A novel composite membrane containing poly [bis (4-aminodiphenyl bissulfonate) phosphoronitrile] (PDAP) flexible chains and acid-base sulfonated polyimide (abSPI, synthesized by one-pot method) was prepared. The influence of different content of PDAP on the performance of composite membrane was explored systematically. The results showed that the conductivity was significantly improved through main-chain-type and side-chain-type –SO3H of the pristine abSPI and introduced PDAP flexible chains, respectively, and the abSPI/0.5% PDAP membrane with the best performance reached 1.17 × 10−1 S cm−1, exceeding N212 (1.12 × 10−1 S cm−1) at room temperature. Moreover, the selectivity of composite membrane based on the Donnan repulsion effect between the N-protonated in PDAP and VO2+ and acid-base effect between –SO3H and N–H reached 0.69 × 105 S min cm−3 (1.43 times of N212). The VRFB single cell equipped with the abSPI/0.5% PDAP membrane showed the best battery performance, with the coulombic efficiency (CE) reaching 97.50% and the energy efficiency (EE) reaching 78.09% at 100 mA cm−2. The results of 300 charging-discharging cycles test showed that abSPI/0.5% PDAP membrane has good long-term cycle stability and excellent service life. The SEM and FTIR results showed that abSPI/0.5% PDAP membrane still had excellent mechanical properties and chemical stability after the 300 cycles test. [Display omitted] •A novel sulfonated polyimide membrane with poly [bis (4-aminodiphenyl bissulfonate) phosphoronitrile] flexible chains was prepared.•The abSPI/0.5% PDAP composite membrane with the best performance reached 1.17 × 10−1 S cm−1, exceeding N212 at room temperature.•The cycle performance of abSPI/0.5% PDAP composite membrane (CE: 94.52%–97.50%, EE: 74.21%–78.13%) is much better than that of N212.