Cation Exchange Membranes with Bi‐Functional Sites Induced Synergistic Hydrophilic Networks for Selective Proton Transport

Abstract Acid recycling via cation exchange membranes (CEMs) has attracted considerable attention from traditional industries and advanced manufacturing because of the economic and environmental advantages. However, current polymeric CEMs merely have constant ion channels by the fixed groups in the matrix and lack the synergy of bi‐functional sites. Herein, a series of dibenzo‐18‐crown‐6 (DB18C6) functionalized sulfonated poly(biphenyl alkylene) membranes is reported. The resultant membranes form phase separation and ordered ion channels by the electrostatic interaction between DB18C6‐H + complexes and the SO 3 − anionic sites, constructing a low‐swelling synergistic hydrophilic network. The prepared membranes have high proton permeation rates of 2.98‐4.85 mol m −2 h ‐1 and extremely low ferrous ion permeabilities, leading to a high H + /Fe 2+ selectivity of ≈3153 at the current density of 10 mA cm ‐2 , which is one order of magnitude higher than the commercial and previously reported membranes via the electrodialysis. These results provide strategies for designing bi‐functional ion exchange membranes for selective ion transport via utilizing crown ether/cation complexes.