Proton exchange membranes containing densely alkyl sulfide sulfonated side chains for vanadium redox flow battery

Due to further increase the performance of aromatic sulfonated proton exchange membrane (PEM) and make it play a better role in vanadium redox flow battery (VRFB), a series of poly(aryl ether sulfone)s containing eight alkyl sulfide sulfonated side chains (8SPAES-xx) are designed and synthesized. Their molecular structure, phase morphology and some selective properties were investigated in detail, respectively. It is confirmed that 8SPAES-xx membranes have clear hydrophilic/hydrophobic phase separation morphology. These membranes with the ion exchange capacity values of 1.08–1.61 mmol/g exhibit excellent ionic conductivity as well as moderate water uptake and good dimensional stability, and their values are in the range of 25–96 mS/cm, 8–28% and 5–17% at 30 °C, respectively. Among them, the proton conductivity of 8SPAES-12 membrane is 82 mS/cm at 30 °C, which exceeds the ionic conductivity of Nafion 117 (79 mS/cm). The membrane also shows high ion selectivity and excellent battery performance. At current density of 60 mA/cm 2 , the highest energy efficiency of VRFB with 8SPAES-12 membrane is 87.3%, which is higher than that of Nafion 117 (83.8%). Furthermore, the efficiency of VRFB with 8SPAES-12 membrane remains good cycle stability.