Functional molecular cross-linked zeolite nanosheets heighten ion selectivity and conductivity of flow battery membrane

Membranes with high ion selectivity and conductivity are critical for the wide application of electrochemical energy conversion and storage devices. Herein, functional molecular cross-linked two-dimensional zeolite nanosheets (ZN) with -NH₂ and -SO₃H groups are prepared and incorporated into sulfonated poly (ether ether ketone) (SPEEK) polymer matrix. These embedded nanosheets act as strong barrier to vanadium ions, while their internal pores provide transport channels for protons. In addition, the side functional groups grafted on ZN not only effectively enhance the surface affinity, but also bind and arrange the sulfonic acid groups of the polymer matrix to construct a continuous fast proton transfer pathway along the interface between SPEEK and ZN. Consequently, the hybrid membranes exhibit synchronously enhanced conductive-ion selectivity and impressive performance with coulombic efficiency (CE) of ~99.0% and energy efficiency (EE) of ~85.0% at 120 mA cm⁻², which is much higher than these of pure SPEEK (CE: ~97.8%, EE: ~78.4%) and Nafion 212 membranes (CE: ~96.3%, EE: ~80.1%). This functional-designed hybrid approach provides a general strategy to develop high-performance proton conductive membranes for energy-related applications.