High-performance SPEEK composite membrane with ultrahigh selectivity enabled by sulfonated PANI for vanadium flow battery

The sulfonated poly(ether ether ketone) (SPEEK) composite membranes (S/SPANI) are prepared by blending sulfonated polyaniline (SPANI), which was synthesized through a post-sulfonation method. With the SPANI contents varying from 1 to 4 wt%, the S/SPANI membranes exhibit excellent physicochemical properties and cell performance, and at loading 3 wt% SPANI, S/SPANI-3 presents a higher proton conductivity (43.3 mS cm-1) and superior ion selectivity (49 x 103 S min cm-3) against SPEEK and Nafion 212. Moreover, its outstanding coulombic efficiency (95.9-98.4%) and energy efficiency (EE: 80.4-70.2%) at the current density of 100-200 mA cm-2 demonstrate an optimized tradeoff of proton conductivity and vanadium ion permeability. The performance optimization guarantees enhanced durability for 600 cycles and stable EE (76%) at 150 mA cm- 2, which originated from the acid-base interaction, synergistic proton network, and interconnected chain structure. So, this provides a facile method to develop high-performance membranes by introducing desirable controllable topological molecular chains to construct synergistic proton transportation networks.