Lewis Acid-Base Interaction Boosting Ion Selectivity of Poly(Ether Ether Ketone)/Polyimide Membrane Toward...

The development of advanced ion-conducting membranes is crucial for improving alkaline zinc-iron flow batteries (AZIFBs), which face a persistent tradeoff between ion selectivity and conductivity. This work presents a sulfonated poly(ether ether ketone)/polyimide (SPEEK/PI) composite membrane engineered via Lewis acid-base interaction. The specific interaction between the -SO₃ ^- groups of SPEEK and the -N= sites of PI creates additional cross-linking points within the polymer matrix. This cross-linked structure effectively suppresses membrane swelling and enhances mechanical stability. Consequently, the composite membrane demonstrates superior ion selectivity by significantly hindering the crossover of active species such as [Fe(CN)₆]^4-. When applied in AZIFBs, the SPEEK/PI membrane enables a notable improvement in electrochemical performance. The battery achieves a high coulombic efficiency (CE) of 98.3%, an energy efficiency (EE) of 89.8%, and a voltage efficiency (VE) of 91.4% during long-term cycling at 80 mA cm^-2, outperforming devices using pristine SPEEK membranes (CE:95.4%; EE: 86.7%; VE: 90.9%). This study provides a cost-effective and efficient membrane design strategy based on molecular interaction, offering a promising alternative for practical flow battery applications.