Highly symmetric spongy porous poly(ether sulfone) membranes with selective open-cells for vanadium flow battery application

Poly(ether sulfone)/sulfonated poly(ether ether ketone) (PES/SPEEK) symmetric spongy porous membranes are prepared for vanadium flow battery (VFB) application. The membrane morphology can be easily controlled by changing the hydrophilic SPEEK content in the cast solution. The performance of the spongy porous PES membranes with different morphologies was studied in detail. The results indicate that the closed spongy pores are more connected and the ultra-thin pore walls are thinner after introducing SPEEK into the cast solution, resulting in lower columbic efficiency (CE) along with higher voltage efficiency (VE). The optimized VFB performance of the PES porous membrane illustrated a CE of 92.98% and VE of 83.60% and the performance remained stable after running for more than 200 cycles. In addition, the prepared PES porous membrane showed an excellent capacity retention capability as well, showing good potential usage in VFBs for long term operation.