Enhancing Nanofluidic Anion‐Selective Transport via Hydrophilic Modification of Ultrathin Conjugated Microporous Polymer Membranes

Efficient ion transport is crucial for both biological and nonbiological processes, such as the maintenance of cellular homeostasis, energy conversion, and mass transfer in the chemical industry. Nanofluidic channels serve as an ideal platform with unique nano-confinement, offering great potential for precisely controlling ion transport. However, the reported nanofluidic channels are restricted by low ion selectivity and high transport resistance because of their discontinuity and randomness. This work presents an ultrathin anion-selective conjugated microporous polymer (CMP) nanofluidic membrane formed on an anodized aluminum oxide (AAO) substrate designed to achieve an excellent ion permselectivity. Hydrophilic 2,2'-Diamino-(1,1'-biphenyl)-4,4'-dicarboxylic acid (DBDA) coordination renders the resulting DBDA-CMP/AAO membrane super-hydrophilic and markedly accelerates anion transport. Additionally, the asymmetric structure, combining an AAO substrate with the DBDA-CMP membrane, introduces unique ionic current rectification, effectively suppressing ion concentration polarization and further enhancing ion permselectivity. In osmotic energy applications, the DBDA-CMP/AAO membrane attained an output power density of 84 W m^-2 at a 500-fold NaCl gradient concentration. This work introduces a novel strategy to enhance the pore environment through hydrophilicity modulation, providing new insights into seawater desalination and ion/molecular transport.