Rational use and reuse of Nafion 212 membrane in vanadium flow batteries

Abstract

Nafion series membranes are widely applied in vanadium flow batteries (VFB) as benchmark separators because of their extremely high chemical/mechanical stability. However, the serious vanadium ions crossover and comparably high price still hinder the large-scale application of Nafion membranes in VFB. Rational use and reuse of Nafion membranes is expected to overcome these two critical issues, which would greatly enhance the cycling performances and reduce the cost of VFB. In this study, we chose the relatively thin (50 μm) and cheap Nafion 212 membrane to investigate the rational use (for fresh membranes) and reuse (for used membranes) protocols in VFB. The structure-property relationship of various pretreated (as-received, water wetted, and acid boiled) Nafion 212 membranes is studied comprehensively. The results demonstrate that the wet Nafion 212 membrane can achieve superior VFB performances including 96% of coulombic efficiency, 77% of energy efficiency, and 0.11% per cycle of capacity fading at a higher current density of 120 mA cm⁻². Our attempt also reveals that the characters of the reused Nafion 212 membranes, such as micro and macro morphologies, mechanical properties, rate and cycling performances, have been well maintained, even after the strict testing procedures which including frequent assembly/disassembly (12 times) of battery and super long period of operation (1500 h), demonstrating that Nafion 212 membrane can be used repeatedly in VFB.