Homogeneous-strengthened SPEEK membrane with ultrahigh conductivity regulated by main/side-chain bisulfonated PEEK for vanadium flow battery

A comblike polymer (SPOS) with a main/side-chain bisulfonated structure has been synthesized with 1,3-propane sulfonate as the pendant chains and poly(ether ether ketone) (PEEK) as the reactant by the combined post-sulfonation and ring-opening grafting reaction. Taking sulfonated PEEK as a membrane matrix, the composite membranes (S/SPOS) are prepared by the solution-blending method with varied contents of bisulfonic SPOS polymer from 10 to 25 wt%. The S/SPOS composite membranes display superior conductivity owing to synergistic enhancement in the intermolecular chain interactions and the homogeneous strengthened transportation channels from main/side-chain bisulfonic acid interconnected networks. S/SPOS-15 shows better CE (96.5-98.5%) and EE (84.7-69.9%) than that of Nafion 212 (CE: 92.3-95.0%, EE: 76.1-63.7%) at 100-200 mA cm-2. Moreover, 600-cycled durability and 77.3 % EE at 150 mA cm-2, and 71.8 h self-discharge time demonstrate its improved reliable structure and cyclic stability. This provides a promising method to prepare high-performance and low-cost membranes with desirable conductivity by homogeneous structural regulation and molecular chain synergistic interactions.