One-step fabrication of porous anion exchange membranes for acid recovery breaking acid permeability–selectivity trade-off

Abstract

Diffusion dialysis (DD) presents a highly promising and cost-efficient approach for acid recovery, yet its performance is often hindered by the acid permeability of anion exchange membranes (AEMs). To address this challenge, a one-step approach has been developed to fabricate porous AEMs. Using brominated polyphenylene oxide (BPPO) as the porous base membrane, imidazole is employed for in-situ crosslinking and cationization. This approach not only retains the inherent porosity (>63.5 %) of the base membrane but also achieves an exceptionally thin selective layer (<0.3 μm), thereby creating abundant free space volume. Through a concurrent enhancement of ion transport sites and crosslinking density, the membrane effectively breaks acid permeability–selectivity trade-off. The optimal IPPO-20h AEM demonstrates a remarkable increase in both the acid dialysis coefficient ($U_{H^{+}}$ = 34.1 × 10⁻³ m/h) and separation factor ($S_{H^{+}/{Fe}^{2+}}$ = 573.8) in the HCl/FeCl₂ system, with enhancements of 4- and 31-fold, respectively, compared to the commercial DF120 AEM, at 25 °C. This high-performance AEM, synthesized via a straightforward and mild process, offers significant potential for large-scale acid recovery applications.