Enhancement in proton conductivity and vanadium resistance of SPEEK-based hybrid membrane induced by incorporating amphoteric GO-DA nanofillers for vanadium flow battery

Abstract

Sulfonated poly(ether ether ketone)-based hybrid membranes (S/GO-DA) have been fabricated through the solution-mixing method, and the introduced graphene oxide (GO) nanofillers functionalized by 2, 4-diaminobenesulfonic acid (DA) afford outstanding physicochemical properties and excellent battery performance for the S/GO-DA membranes. At low loading 1 wt% GO-DA nanofillers, the S/GO-DA-1 membrane gives the highest ion selectivity (45.4 × 103 S min cm−3) and the lowest vanadium ion permeability (7.38 × 10−7 cm2 min−1), which is superior to Nafion 212 (3.0 × 103 S min cm−3, 42.5 × 10−7 cm2 min−1) and SPEEK (3.85 × 103 S min cm−3, 94.4 × 10−7 cm2 min−1), respectively. Moreover, the better energy efficiency (81.1–68.6 %) and longer self-discharge time (78.3 h) of S/GO-DA-1 at 100–200 mA cm−2 current density further prove its good structure stability and durability, elucidating the balanced proton conductivity and vanadium resistance is helpful to enhance the membrane performance. In addition, after cycling at 150 mA cm−2 current density for at least 200 cycles, 76.3 % energy efficiency and 26.9 % charge retention rate are given, illustrating the combined physical barrier of GO-DA nanofillers and the acid-base interaction contribute a synergistic promoting effect on enhancing the battery efficiency of the S/GO-DA hybrid membranes. Therefore, the present work provides a facile method to construct a high-performance proton exchange membrane by developing 2D nanostructured nanofillers containing various chemical covalent-bonded functional amphoteric molecular chains.