Structural Effect of the Hydrophobic Block on the Chemical Stability of Ion-Conducting Multiblock Copolymers for Flow Battery

Abstract

Four sulfonated poly(p-phenylene)-based ionomer materials with different hydrophobic block structures are synthesized in order to investigate the effect of the hydrophobic block structure on the durability of ionomer membrane in vanadium redox flow batteries (VRFBs). The structural differences of the hydrophobic blocks scarcely affect the physical, electrochemical, and morphological properties of the block copolymer-type ionomers. On the contrary, according to an ex situ soaking test and an in situ VRFBs cell test, the structural differences of the hydrophobic block greatly affect the chemical stability of the ionomer membranes. Among the four ionomers, the sPP-b-PSK membrane shows outstanding cell performance (Coulombic efficiency of 99.3% and energy efficiency of 72.6%) as well as excellent chemical stability even after long-term operation of 2 000 cycles. These results are conceptually helpful for designing chemically stable ionomers.