Hydrogen‐Bond Anchored Channel‐Microenvironment Engineering in Polymer Membranes for Efficient Lithium Extraction

ABSTRACT The creation of synthetic membranes that mimic the high selectivity and flux of biological ion channels remains a major challenge in separation science. Precise control over chemical microenvironment within sub‐nanometer pores is critical but notoriously difficult to achieve in scalable materials like amorphous polymers. Here we report a strategy for engineering the microenvironments of confined channels in a polymer of intrinsic microporosity (PIM) by using hydrogen bonding to uniformly anchor oligoether chains onto the pore walls. The enhanced confinement effect resulting from this anchoring increases steric limitation for larger ions (e.g., Mg 2+ ) and strengthens their ion‐channel interactions. Concurrently, the uniformly distributed oligoether chains establish a synergistic transport pathway for small ions (e.g., Li + ). The resulting membrane exhibits exceptionally high selectivity for monovalent ions over divalent ions (Li + /Mg 2+ selectivity of >270) while maintaining a high Li + flux (>0.6 mol m −2 h −1 )—an order of magnitude improvement compared to state‐of‐the‐art polymeric membranes. When deployed for direct lithium extraction from salt‐lake brine, the membrane achieves a lithium recovery rate of 268 g m −2 day −1 and low energy consumption (7.26 Wh g Li −1 ).