Robust Linkage‐Encoded Covalent Organic Framework Membranes Sustain Selective Ion Transport for Energy Harvesting From Concentrated Acids

ABSTRACT Achieving simultaneously high ion permselectivity and chemical robustness in concentrated electrolytes remains a central challenge for membrane‐based technologies, because strong electrostatic screening suppresses charge‐based exclusion while corrosive acids and bases accelerate material degradation. Here we report a molecular strategy to construct robust linkage‐encoded covalent organic framework (COF) membranes in which short‐range ion‐framework interactions are embedded directly within fully conjugated enaminone linkages lining vertically aligned nanochannels. By holding framework topology and pore architecture constant while varying only the linkage chemistry, we show that the linkage microenvironment governs ion selectivity, transport efficiency, and chemical stability. Periodic enaminone motifs create persistent coordination environments and hydrogen‐bond networks that remain effective at high ionic strength, enabling ultrafast proton transport exceeding Nafion 212 by more than fivefold. The membrane preserves crystallinity and pore alignment and maintains performance after exposure to 12 M H 2 SO 4 at 110°C and under concentrated alkaline conditions. To demonstrate performance under extreme conditions, it delivers a peak osmotic power density of 2422.9 W m −2 under a 12 M || 0.01 M H 2 SO 4 gradient while maintaining stable continuous operation. This linkage‐encoding paradigm provides a general route to ion‐selective, chemically resilient membranes for reliable ion transport and electrochemical technologies operating in chemically extreme electrolytes.