Multi-Port Spraying: A Method for Preparation of Ionic Cross-linking Membranes

The properties of ion exchange membranes are largely dependent on their chemical composition and preparation methods. Traditional methods for ionic cross-linking, such as casting or decantation, often result in nonuniform membranes with defects, such as holes, due to precipitation issues. Additionally, regulating the degree of ionic cross-linking is challenging, leading to less research focus compared to covalent cross-linking. In this study, we introduce an ionic cross-linking method for preparing anion exchange membranes (AEMs). Our approach involves spraying quaternary ammonia poly(N-methylpiperidine-co-p-terphenyl) (QAPPT) and Nafion solution from separate ports onto an ultrasonic atomization surface, enabling ionic cross-linking when sprayed onto a heated aluminum foil substrate. This method produces complete and uniform membranes with enhanced properties, including improved swelling degree (SD), water uptake (WU) and tensile strength. Notably, the 5% Nafion ion-cross-linked membrane exhibits ionic selectivity, with hydroxide ion conductivity of 25% faster than carbonate ions at 80 °C. The versatility of this multiport spraying technique allows for the preparation of ionic cross-linking membranes using various anion and cation exchange polymers, offering significant potential for advancing membrane material development.