Construction of ultrathin PANI nanostructure on cation-exchange membranes for selective lithium extraction

The development of thin, charge-selective surface layers on cation exchange membranes (CEMs) is crucial for advancing electrodialysis technology, particularly for achieving both high ion permeability and precise selectivity. In this study, we developed an innovative approach to fabricate ultrathin polyaniline (PANI) nanolayers on CEM substrates through pre-adsorption of protonated aniline monomers followed by in-situ polymerization. The resulting membranes feature a uniform Turing-type nanostructure through FESEM characterizations, which significantly enhances surface positive charge density. Our optimized membrane demonstrates exceptional performance, achieving a Li + /Mg 2+ selectivity of 6.75 while maintaining a high lithium permeation rate of 0.18 mmol·cm −2 ·h −1 . These results compare favorably with current state-of-the-art permselective membranes and surpass the commercial membrane CSO (5.26 for the Li + /Mg 2+ selectivity and 0.16 mmol·cm −2 ·h −1 for the lithium permeation rate). Mechanistic studies including electrochemical impedance spectroscopy and molecule dynamics simulation reveal that PANI layers with optimal thickness and pore structure minimize resistance to monovalent cations while effectively blocking divalent cations, enabling efficient ion separation during electrodialysis. This work highlights the remarkable potential of nanostructured PANI layers for selective ion transport and provides a practical strategy for designing advanced electrodialysis membranes. The simple fabrication method and outstanding performance characteristics make this approach particularly promising for lithium extraction and other ion separation applications.