Highly Stable Polybenzimidazole Composite Membrane with a Durable Separation Layer by Interfacial Polymerization

Thin-film composite (TFC) membranes prepared by interfacial polymerization have been widely used for membrane separation. However, the most commonly used polyamide-TFC membranes suffer from relatively low stability due to the hydrolysis of amido bonds in aqueous acidic or alkaline media. Herein, we report a highly stable polybenzimidazole (PBI)-TFC membrane using the interfacial condensation reactions between 3,3'-diaminobenzidine (DAB) in the aqueous phase and benzene-1,3,5-tricarbaldehyde (BTA) in the organic phase. By decreasing the pH of the aqueous phase, the dispersity of DAB molecules at the oil-water interface is enhanced, boosting DAB-BTA reactions to form a denser and thinner PBI film of around 296 nm. The synergistic effects of the PBI film thickness and packing conformations of PBI chains produce a permeable (area resistance: 0.11 Ω cm²) and selective (permeability: 2.27 × 10^-6 cm² h^-1) PBI-TFC membrane, which can keep the structure stable in strongly acidic and oxidizing aqueous conditions. Exemplified in an aqueous acidic vanadium flow battery, it displays a high energy efficiency of >80% at 160 mA cm^-2, which runs stably for over 300 cycles, confirming the stability and reliability of PBI-TFC membranes. This membrane design approach offers an effective strategy to enhance the permeability, selectivity, and stability of TFC membranes.