Preparation and properties of sulfonated poly (aryl ether sulfone)s proton exchange membranes based on amino graft for vanadium flow battery

A series of aromatic proton exchange membranes (PAES-4S-xx) with tetrasulfonated side alkyl chains in repeated structural units are conveniently prepared by two-step reaction using 3,3′-(3″-aminophenyl)-4,4′-difluorodiphenylsulfone (2NH 2 -DFDPS), 4,4′-difluoro-diphenylsulfone, 4,4′-dihydroxybiphenyl and sodium 2-bromoethyl sulfonate as starting materials. Their chemical structure and physical properties are systematically studied. The incorporation of locally dense flexible side alkyl chains effectively endows the obtained ionic membranes based on PAES-4S-xx with high proton conductivity and moderate water uptake and swelling ratio. The corresponding values are between 38 and 98 mS/cm, 10 %–26 % and 6 %–18 % (30 °C), respectively, which increases with the increase of sulfonic acid content. In VRFB tests, the coulomb efficiency (CE) and energy efficiency (EE) of a single battery based on PAES-4S-24 membrane reach 95.8 % and 86.6 % at current density of 40 mA/cm 2 , respectively, higher than that of the single battery assembled by Nafion 115 (CE:90.7 %, EE:81.5 %). In addition, the single battery based on PAES-4S-24 also shows good stable performance during cyclic charging and discharging.