A novel porous polyimide membrane with ultrahigh chemical stability for application in vanadium redox flow battery

The chemical stability of membranes is critical for the application in vanadium redox flow battery (VRFB). In this work, a novel porous cross-linked polyimide membrane (PCrPI) with ultrahigh chemical stability is prepared by using I3-cyclodextrin (I3-CD) as a template. The unique cross-linking structure and imidazole group with Donnan effect of PCrPI membrane can effectively hinder the migration of vanadium ions. Meanwhile, the imidazole group and porous structure of the PCrPI membrane can also enhance ionic transfer and reduce area resistance. In VRFB tests, the PCrPI membrane exhibits higher coulomb efficiency (CE: 96.3-99.6%) and energy efficiency (EE: 67.9-88.9%) than commercial Nafion 212 membrane (CE: 74.3-94.8%; EE: 67.7-77.5%) at the current density of 40-200 mA cm-2. In addition, the charge-discharge cycles of VRFB with the PCrPI membrane are performed 2250 times, and the running time of PCrPI-10 membrane is among the top level compared with previously reported membranes. Meanwhile, the excellent durability of PCrPI-10 membrane is also explained through theoretical calculation with natural bond orbital charge and binding energy. The results show that the application of PCrPI-10 membrane in VRFB will embrace a bright future.