π‐π Interaction Engineered Membranes for pH‐Neutral Aqueous Organic Redox Flow Batteries

ABSTRACT The practical implementation of pH‐neutral aqueous organic redox flow batteries (AORFBs) hinges on the development of high‐performing ion exchange membranes, and the tradeoff between membrane conductivity and selectivity remains a grand challenge for the design of membranes. Here, we designed a series of anion exchange membranes specifically for pH‐neutral AORFBs by incorporating a rigid and planar 9,10‐diphenylanthracene (DPHA) moiety into the membrane backbone. The introduction of DPHA could induce strong intermolecular π‐π interactions, driving the aggregation of positively charged functional groups and enhancing the membrane dimensional stability. These interactions also facilitated the formation of well‐defined and uniformly distributed ion conduction pathways and promoted ion transport. Consequently, the representative QTPDA‐30% membrane achieved an area‐specific resistance of 0.52 Ω cm 2 and enabled stable cell cycling for over 700 cycles (more than 240 h) with a minimal capacity fade rate of 0.00125% per cycle (0.08% per day). This study highlights the effectiveness of molecular engineering strategy by exploiting the secondary interactions between polymer chains in constructing high‐performing ion exchange membranes for long lifetime and efficient pH‐neutral AORFBs toward grid‐scale energy storage.