Sulfonated poly(ether ether ketone)/lignin composite membrane with abundant hydrogen bonds synergistically enhanced conductivity and selectivity in zinc‑iron flow battery

A SPEEK/lignin composite membrane is developed to overcome the conductivity-selectivity trade-off. • A hydrogen-bond network between lignin and SPEEK effectively blocks crossover of large [Fe(CN) 6 ] 4− ions. • Improved hydrophilicity facilitates electrolyte uptake and creates better ion transport channels. • The composite membrane enables excellent cycling stability with significantly enhanced coulombic efficiency. Zinc‑iron flow batteries are limited by membrane conductivity-selectivity trade-off. We develop sulfonated poly(ether ether ketone)/lignin (SPEEK/L) composite membranes. The abundant hydroxyl groups (–OH) in lignin interact with sulfonic acid groups (–SO 3 − ) in SPEEK to form a hydrogen-bond network. This network appreciably blocks the crossover of large [Fe(CN) 6 ] 4− ions, enhancing selectivity. The improved membrane hydrophilicity facilitates electrolyte uptake, creating better ion transport channels and reducing membrane resistance. The battery achieves 97.5% coulombic efficiency over 300 cycles at 80 mA/cm 2 , which is much higher than those of pure SPEEK. This synergistic strategy boosts conductivity and selectivity for advanced flow batteries. Download: Download high-res image (200KB) Download: Download full-size image