Poly(biphenyl piperidinium) Amphiphilic Membranes Functionalized with Propyl Sulfonic Acid and Octadecyl Side Chains for Vanadium Redox Flow Batteries

A series of amphiphilic ion exchange membranes (50PS–PBP-x) containing propyl sulfonic acid, long octadecyl side chains, and piperidinium quaternary ammonium structures are designed and prepared by the Menshutkin reaction of poly(biphenyl piperidinium)s with sodium 3-bromopropanesulfonate and 1-bromooooctadecane. The surface morphology and microphase separation structures of the amphiphilic membranes are observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Their water uptake and swelling ratio are in the range of 9.2–20.2 and 3.7–7.8%, respectively. The area resistances and vanadium ion permeabilities for these membranes are in the range of 0.35–0.51 Ω cm2 and 1.9 × 10–7–4.7 × 10–7 cm2 min–1, respectively. The vanadium redox flow battery based on the representative 50PS–PBP-30 membrane also exhibits good performance. Its maximum energy efficiency reaches 81.7% and does not obviously decline after 200 cycles of running.