Abstract:

 A series of novel ion exchange membranes (IEM), based on sulfonated poly (ether ether ketone) (SPEEK) with different weight ratios of sulfonated graphene oxide (SGO) loadings, were employed and investigated in vanadium redox flow battery (VRB). SPEEK was obtained by sulfonation of poly (ether ether ketone) (PEEK) in concentrated H2SO4, SGO is fabricated by grafting sulfonic groups to GO via a facile method. SPEEK/SGO membranes were prepared by solution casting method. GO and SGO were characterized by Fourier transform infrared spectroscopy (FT-IR) and the physicochemical properties of all membranes were measured by water uptake (WU), ion exchange capacity (IEC), proton conductivity, vanadium ion permeability, mechanical properties, oxidation stability and single cell performance. The result of FT-IR indicated that –SO3H groups were successfully grafted to GO, SEM images revealed the good dispersion of SGO in the SPEEK matrix. And other results showed that added SGO increased the WU and proton conductivity of composite membranes, the proton selectivity of S/SGO-1 membrane (14.14×104 S·min·cm3) was 66.5% higher than that of SPEEK (8.49×104 S·min·cm3). In single cell test, VRB with S/SGO-1 showed coulombic efficiency (CE) of 95.5%, VE of 92.0% and EE of 87.8% with good cycle stability, and the self-discharge time of VRB with S/SGO-1 membrane (78 h) is longer than that of Nafion115 (30 h). All experimental results indicate that incorporation of SGO can reduce the vanadium permeability and maintain high VE of SPEEK at the same time. S/SGO IEMs, especially S/SGO-1 shows promising prospects for VRB.

Key words: vanadium redox flow battery, sulfonated poly (ether ether ketone), sulfonated graphene oxide, proton selectivity, cell efficiency