No abstract

A series of novel composite membranes, based on sulfonated poly(ether ether ketone) (SPEEK) with various graphene oxide (GO) loadings, were employed and investigated in vanadium redox flow battery (VRFB) for the first time. The scanning electron microscopy images of the composite membranes revealed the uniform dispersion of GO nanosheets in the polymer matrix due to the interaction between GO and SPEEK, as confirmed by Fourier transform infrared spectra. The mechanical and thermal parameters of the composite membranes increased, while the VO 2+ permeability decreased with increasing GO content.Random embedding of GO nanosheets in the membranes can serve as effective barriers to block the transport of vanadium ion, resulting in a significant decrease of vanadium ion permeability. The VRFB assembled with the composite membrane exhibited highly improved cell parameters and strikingly long cycling stability compared with commercial Nafion 117 membrane. With the protection of porous PTFE substrate, the pore-filling SPEEK/GO composite membrane based on VRFB ran for 1200 cycles with relatively low capacity decline.

No abstract

Nafion membranes are now the most widely used membranes for long-life vanadium flow batteries (VFBs) because of their extremely high chemical stability. Today, the type of Nafion membrane that should be selected and how to pretreat these Nafion membranes have become critical issues, which directly affects the performance and cost of VFBs. In this work, we chose the Nafion 115 membrane to investigate the effect of the pretreatment process (as received, wet, boiled, and boiled and dried) on the performance of VFBs. The relationship between the nanostructure and transport properties of Nafion 115 membranes is elucidated by wide-angle X-ray diffraction and small-angle X-ray scattering techniques. The self-discharge process, battery efficiencies, electrolyte utilization, and long-term cycling stability of VFBs with differently pretreated Nafion membranes are presented comprehensively. An online monitoring system is used to monitor the electrolyte volume that varies during the long-term charge-discharge test of VFBs. The capacity fading mechanism and electrolyte imbalance of VFBs with these Nafion 115 membranes are also discussed in detail. The optimal pretreatment processes for the benchmark membrane and practical application are synthetically selected.

No abstract