Optimized S-PEEK Membranes with High Coulombic Efficiency for Vanadium Redox Flow Battery

Nowadays, vanadium redox flow battery (VRFB) has been considered one of the most promising approach to efficiently store renewable energies in large-scale. Specifically, most of its advantages is related to the decoupled energy storage and power, the high energy efficiency, the fast response and ambient temperature operations, the flexible design and safety, the long cycling stabilities1-6. Commonly, in such battery type, Nafion has been used as membrane in VRFB, although it suffers for high vanadium crossover, and high cost. Therefore, these drawbacks negatively affect the commercial widespread of VRFBs7. To replace the widely used but expensive perfluorinated Nafion membranes, great efforts have been made to search alternative ones; among all candidates, sulfonated poly(ether ether ketone) (SPEEK)-based membrane seems to be the most suitable to replace Nafion membrane because of its lower cost, high proton to vanadium ion selectivity, if only the poor stability be solved8. In this contribution, S-PEEK membranes with different sulphonation degrees and SiO-NH2 filler contents were prepared and, after physic-chemical and morphological characterizations, tested in lab-scale VRFB system by means of several consecutive charge-discharge cycles measurements. The VRFB test performed using the prepared S-PEEK membranes revealed higher Coulombic efficiency respect to commercial Nafion, used as reference.