Nanostructured Thin-Film Composite Membranes for Redox Flow Electrochemical Separations

Fermentative organic acid production has been recognized as a sustainable approach for waste valorization. However, the complex organic acid distribution and dilution of fermentation products pose challenges for selective acid recovery, requiring energy-intensitve downstream separation processes. Redox couple-incorporated electrodialysis systems have recently shown promise for energy-efficient organic acid separation, although the lack of suitable membrane designs for effectively separating similar organic ions remains a hurdle. Herein, thin-film composite membranes with a nanostructured polyelectrolyte top layer for selective organic acid separation are demonstrated. Catalyst-free polymer modification methods are developed to molecularly tailor the hydrophobicity of the polyelectrolytes and their phase behaviors. On-surface phase separation of the polymers, synergistically tuned by the polymer modification, enables the formation of a nanoscale and uniform active layer on the membrane support. The nanostructured layer enhances the permeability of organic acids with higher molecular selectivity, overcoming a conventional flux-selectivity trade-off. Furthermore, redox-mediated electrochemical separation is demonstrated for the recovery of organic acids from real fermentation effluents. Selective organic enrichment with low energy consumption is achieved by taking advantage of the nanostructured membranes and reversible redox reactions. This study shows the potential of nanostructured polyelectrolyte composite membranes integrated with a redox flow electrochemical system for realizing valuable organic ion recovery with high selectivity and energy-efficiency.