Sulfonated Polyamine-Based Thin Film Composite Membranes with Fast and Selective Ion Transport for Vanadium Redox Flow Batteries

In a vanadium flow battery (VFB) system, the design of an efficient ion conductive membrane (ICM) is crucial to break the trade-off between ion selectivity and conductivity. Thin film composite (TFC) membranes hold great promise to solve this problem. Herein, we synthesized grafted polyethylenimines (PEIs) with sulfonic acid groups and adopted them as building blocks to produce a series of TFC membranes with the ∼80 nm-thick polyamine selective layer via interfacial polymerization (IP). The highly cross-linked polyamine network acts as a strong barrier to vanadium ions, while the negatively charged grafted sulfonic acid groups significantly improve the proton transport. The VFB equipped with the polyamine membrane exhibits enhanced performance with a Coulombic efficiency (CE) of 98.0% at a current density of 120 mA cm–2, along with an energy efficiency (EE) of 85.9%. This work provides an innovative strategy to design high-performance TFC membranes in VFB systems.